#2. How do electrode defects affects it's I-V properties?

Introduction:

Electrode defects can have a significant impact on the I-V properties (current-voltage characteristics) of an electrode. The specific effects of electrode defects on I-V properties depend on the type and severity of the defect. Some possible effects of electrode defects on I-V properties include:

1. Increased resistance: If the electrode has defects that increase its resistance, the I-V curve will show a decrease in current for a given voltage. This is because the current flow through the electrode is hindered by the increased resistance.
2. Non-ohmic behavior: In ideal conditions, the I-V curve of an electrode should be linear, following Ohm's Law. However, electrode defects can cause deviations from this linear behavior, resulting in non-ohmic I-V curves. For example, a defect may cause the electrode to exhibit rectifying behavior, meaning that the current flow is significantly higher in one direction than the other.
3. Shifted or distorted I-V curve: Depending on the type and location of the defect, the I-V curve may shift or become distorted. This can make it difficult to accurately measure or predict the electrode's performance.
4. Reduced stability: Electrode defects can also reduce the stability of the electrode, causing changes in its I-V properties over time. This can be especially problematic in applications where the electrode is frequently used or exposed to harsh conditions.

Overall, electrode defects can significantly impact an electrode's I-V properties, which can affect its performance in various applications. It is therefore important to carefully monitor and control for electrode defects in order to ensure optimal performance. An example of the electrode size-dependent elsewhere. A typical electrode size-dependent I-V behavior is shown in Figure 1. 

Figure1: Electrode size dependent-I-V response(example)

 Does a defective surface have a different vertical I-V response if the electrode is good?

Yes, a defective surface can have a different vertical I-V response compared to a non-defective surface, even if the electrode is good. This is because defects on the surface of a material can affect its electronic properties, such as its conductivity, charge transport, and carrier lifetime. These changes can lead to variations in the electrical response of the material, including its I-V properties.

For example, if a surface defect creates a local trap state that captures and traps charge carriers, it can reduce the measured current in the vertical I-V response. Alternatively, if the defect creates a non-uniform electric field that alters the local carrier mobility or density, it can result in changes to the slope or shape of the I-V curve.

In general, defects on the surface of a material can have complex and varied effects on its electrical response, and the specific nature of these effects will depend on the type and location of the defect, as well as the properties of the surrounding material and electrode. Therefore, it is important to carefully characterize and control for surface defects in order to accurately interpret and understand the electrical response of a material. find more help here. 

 #1# What is materials science and technology? Roles of scientist and engineer.

Introduction: Materials Science and Technology (MST) is a field of study that investigates the properties and behavior of various materials, such as metals, polymers, ceramics, and composites. It is an interdisciplinary field that combines elements of physics, chemistry, engineering and applied mathematics to understand the relationships between the structure, properties, processing, and performance of materials (figure 1).Figure.1. Materials science connections

Figure.1. Materials science connections

Materials scientists and technologists seek to develop new materials with unique properties and improve existing materials. They investigate the structure of materials at various scales, from the atomic and molecular level to the macroscopic level, and use this knowledge to design materials with desired properties. They also study how materials respond to different conditions, such as temperature, pressure, and stress.

Materials science and technology have a wide range of applications, including aerospace and transportation, electronics, energy, biomedical engineering, and nanotechnology. It plays a critical role in the development of new technologies and products and in the advancement of industries that rely on materials.

What are the major roles of materials scientists and engineers?

Materials scientists and engineers play a critical role in developing and improving materials that are used in various industries. Here are some of the major roles they play:

1. Research and development: Materials scientists and engineers conduct research to develop new materials with desired properties or improve existing materials. They work on materials at the atomic and molecular level and use techniques such as X-ray diffraction, microscopy, and spectroscopy to study their structure, properties, and behavior.
2. Material selection: Materials scientists and engineers select the appropriate materials for a particular application based on their properties, cost, availability, and environmental impact. They consider factors such as strength, durability, corrosion resistance, thermal and electrical conductivity, and toxicity.
3. Testing and characterization: Materials scientists and engineers test and characterize materials to determine their properties, such as strength, hardness, elasticity, and ductility. They use various techniques like mechanical testing, thermal analysis, and spectroscopy.
4. Process development: Materials scientists and engineers develop and optimize processes for producing materials with desired properties. They consider factors such as temperature, pressure, composition, and time to control the structure and properties of the materials.
5. Quality control: Materials scientists and engineers ensure that materials meet the required standards and specifications for their intended use. They develop and implement quality control procedures to ensure the consistency and reliability of the materials.
6. Problem-solving: Materials scientists and engineers solve problems related to materials'      performance and failure. They use their knowledge of materials' properties and behavior to identify the root causes of the problems and develop solutions to prevent them from recurring.

Figure2: Laboratory activities to make something new for science and technology

Overall, materials scientists and engineers play a critical role in advancing technology and improving the quality of life by developing and improving the materials that are used in various industries. More about science and technology help.

Low power and high power semiconductor devices and major application area.

 Introduction:

Low power and high power semiconductor devices are categorized based on their ability to handle power and current levels. Here are some of the major low power and high power semiconductor devices:

Low Power Semiconductor Devices:

Bipolar Junction Transistors (BJTs)

Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)

Junction Field-Effect Transistors (JFETs)

Small Signal Diodes

Zener Diodes

Schottky Diodes

High Power Semiconductor Devices:

Insulated Gate Bipolar Transistors (IGBTs)

Power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)

Thyristors (Silicon Controlled Rectifiers (SCRs), Triacs)

Power Diodes

Gallium Nitride (GaN) Devices

Silicon Carbide (SiC) Devices

Low power:

Low power semiconductor devices are typically used in applications where small currents and voltages are involved, such as in signal processing and low-power electronics. These devices have low power dissipation, low voltage drop, and high input impedance, making them suitable for low power applications.

High power: 

High power semiconductor devices, on the other hand, are used in applications where high current and voltage levels are required, such as in power electronics, electric vehicles, and renewable energy systems. These devices have high power dissipation, high voltage blocking capability, and low on-state resistance, making them suitable for high power applications.

Overall, the choice of low power or high power semiconductor devices depends on the specific application requirements, such as power level, voltage level, and switching frequency.

Applications:

Semiconductor devices have a wide range of applications in various fields, including electronics, telecommunications, computing, energy, and transportation. Here are some of the major application areas of semiconductor devices:

Electronics: Semiconductors are the foundation of modern electronics, and they are used in a wide range of devices, such as smartphones, computers, televisions, and gaming consoles. They are also used in sensors, amplifiers, oscillators, and memory devices.

Telecommunications: Semiconductors are used in telecommunications equipment, such as cell phones, base stations, and routers. They are also used in fiber optic cables, satellite communication systems, and microwave devices.

Computing: Semiconductors are essential components in computing devices, such as processors, memory chips, and storage devices. They are also used in graphics cards, sound cards, and other peripheral devices.

Energy: Semiconductors play a critical role in renewable energy systems, such as solar panels and wind turbines. They are also used in power electronics, such as inverters, rectifiers, and DC-DC converters.

Transportation: Semiconductors are used in various transportation systems, such as electric vehicles, hybrid vehicles, and aircraft. They are also used in control systems for engines, brakes, and suspension systems.

Overall, semiconductor devices have revolutionized many aspects of modern life, and their applications are constantly expanding as new technologies and innovations emerge. Please find more here.

What is green energy mission(GEM)? Key area of GEM? Si, GaN, SiC, GaAs, special Ga2O3

 Introduction: 

The Green Energy Mission in semiconductor research field focuses on developing energy-efficient technologies and processes to reduce the environmental impact of semiconductor manufacturing and promote sustainable energy solutions. Semiconductor manufacturing is an energy-intensive process that requires a significant amount of electricity and produces greenhouse gases and other pollutants. The Green Energy Mission seeks to address these environmental concerns by developing new technologies and processes that reduce energy consumption and carbon emissions.

Key Green areas: 

Some of the key areas of research in the Green Energy Mission include:

Energy-efficient semiconductor manufacturing: Researchers are developing new techniques to reduce energy consumption and carbon emissions in semiconductor manufacturing, such as using renewable energy sources, optimizing manufacturing processes, and developing energy-efficient devices.

Renewable energy: Semiconductors play a critical role in renewable energy systems, such as solar panels and wind turbines. Researchers are working to improve the efficiency and reduce the cost of these systems to promote widespread adoption.

Energy storage: Semiconductor devices are used in energy storage systems, such as batteries and capacitors. Researchers are developing new materials and processes to improve the performance and reduce the environmental impact of these systems.

Energy harvesting: Researchers are developing semiconductor-based technologies to harvest energy from renewable sources, such as solar and kinetic energy, to power small devices and sensors.

Overall, the Green Energy Mission in semiconductor research aims to develop sustainable and energy-efficient technologies that promote environmental sustainability and reduce the dependence on fossil fuels.

Yes, here is a list of some of the commonly used power semiconductor materials:

Semiconductor materials:

Silicon (Si): Silicon is the most widely used material for power semiconductor devices due to its abundance, low cost, and excellent electrical properties. It is used in devices such as diodes, thyristors, and insulated gate bipolar transistors (IGBTs).

Gallium nitride (GaN): GaN is a wide bandgap semiconductor material that offers superior performance compared to silicon in terms of efficiency, switching speed, and power density. It is used in devices such as power transistors, diodes, and rectifiers for high-frequency and high-power applications.

Silicon carbide (SiC): SiC is another wide bandgap semiconductor material that offers superior performance compared to silicon, especially at high temperatures and high voltages. It is used in devices such as Schottky diodes, MOSFETs, and thyristors for high-power and high-temperature applications.

Diamond: Diamond is an emerging power semiconductor material that offers the highest thermal conductivity, allowing for better heat dissipation and higher power density. It is still in the research and development stage, but has the potential to revolutionize power electronics technology.

Gallium arsenide (GaAs): GaAs is a high-performance semiconductor material that offers superior electron mobility and high-frequency performance. It is used in devices such as microwave transistors, amplifiers, and switches for telecommunications and defense applications.

Overall, power semiconductor materials play a critical role in the development of power electronics technology, and each material has its unique advantages and limitations depending on the application requirements. 

However, Gallium Oxide (Ga2O3) is another emerging wide bandgap semiconductor material that has shown promise for high-power and high-voltage applications. Ga2O3 has a much wider bandgap than silicon, GaN, and SiC, making it suitable for use in power devices that require high breakdown voltage, high current density, and low on-resistance. Importance of power semiconductor device for green energy can be easily understand from here. Fig 1 shows a brief relation of 

Figure 1: Operating frequency and capacity with semiconductor material. 

Some of the potential feasibility and concerns of Ga2O3 as a power semiconductor.

High breakdown voltage: Ga2O3 has a high critical field strength, which allows it to withstand higher voltages without breakdown.

High current density: Ga2O3 has a high electron mobility, which allows it to carry more current than other wide bandgap materials.

Low on-resistance: Ga2O3 has a low specific on-resistance, which means that it can operate at lower voltages and consume less power.

Low cost: Ga2O3 is abundant and relatively low-cost compared to other wide bandgap materials.

Some of the potential applications of Ga2O3 power devices include high-voltage power supplies, electric vehicles, renewable energy systems, and high-power electronics for aerospace and defense.

Although Ga2O3 is still in the early stages of development, researchers are working on improving the quality of the material and developing new device structures to harness its full potential as a power semiconductor material. like any emerging semiconductor material, Gallium Oxide (Ga2O3) has some drawbacks that need to be addressed before it can be widely adopted in power electronics applications. Some of the major drawbacks of Ga2O3 include:

Crystal quality: Ga2O3 is a relatively new material, and its crystal quality is not yet as good as other wide bandgap materials such as SiC and GaN. Poor crystal quality can lead to defects and reduced performance in power devices.

Fabrication challenges: Ga2O3 is a complex material to fabricate into power devices, and the existing processes are not as mature as those for SiC and GaN. Developing reliable and scalable fabrication processes will be critical to the commercialization of Ga2O3 power devices.

Thermal conductivity: While Ga2O3 has a high breakdown voltage and low on-resistance, its thermal conductivity is lower than that of other wide bandgap materials. This can lead to higher operating temperatures and thermal management challenges in power devices.

Limited availability: While Ga2O3 is abundant, the supply of high-quality material for power electronics applications is limited. Developing cost-effective and scalable methods for producing high-quality Ga2O3 will be important for its widespread adoption.

Overall, while Ga2O3 has many potential advantages as a power semiconductor material, there are still several technical challenges that need to be overcome before it can be widely adopted in power electronics applications. Researchers are actively working on addressing these challenges to unlock the full potential of Ga2O3 as a power semiconductor material. Please find more information here.

Defects and feasibility of p-Ga2O3 potentials and challenges for Green energy mission.

Introduction:

Gallium oxide (Ga2O3) is a complex material with many possible defects that can arise during its growth and processing. The basic crystal structure of Ga2O3 is shown in figure 1 of most stable beta-phase. 

Figure 1: Beta phase crystal structure of Ga2O3

Some of the most common defects in Ga2O3 include:

Defects in Ga2O3:

Oxygen vacancies: Oxygen vacancies are defects in which an oxygen atom is missing from the crystal lattice. These defects can create localized states in the bandgap, leading to changes in the electrical and optical properties of the material.

Gallium vacancies: Gallium vacancies are defects in which a gallium atom is missing from the crystal lattice. These defects can also create localized states in the bandgap and affect the electronic properties of the material.

Point defects: Point defects are localized disruptions in the crystal lattice, such as interstitial atoms or impurities. These defects can alter the electrical and optical properties of the material, as well as affect its mechanical and thermal properties.

Dislocations: Dislocations are line defects in the crystal lattice that can arise during crystal growth or processing. These defects can affect the mechanical and electrical properties of the material and reduce its performance in power devices.

Grain boundaries: Grain boundaries are interfaces between different crystal grains in the material. These interfaces can create defects and alter the electrical and mechanical properties of the material. 

An example of dislocation is shown in figure 2.

Figure 2: Dislocation in Ga2O3 surface and dimples due to etching 

Overall, understanding and controlling the defects in Ga2O3 is critical for developing high-quality material for power electronics applications. Researchers are actively working on characterizing and controlling these defects to improve the performance and reliability of Ga2O3 power devices.

P-type Ga2O3:

Although it is more difficult than making n-type Ga2O3. The challenge in making p-type Ga2O3 is that the native defects in the material tend to be n-type, which makes it difficult to introduce p-type dopants such as magnesium (Mg) or zinc (Zn).

One approach to making p-type Ga2O3 is to introduce acceptor dopants such as Mg or Zn into the material and then anneal the sample under oxygen-deficient conditions. This can create oxygen vacancies in the material, which can then capture electrons and create holes, resulting in p-type behavior.

Another approach is to use co-doping, in which both an acceptor dopant (e.g., Mg) and a compensating donor dopant (e.g., Si) are introduced into the material. The donor dopant can introduce electrons into the material to compensate for the holes created by the acceptor dopant, resulting in p-type behavior.

While p-type Ga2O3 has been demonstrated in the laboratory, it is still challenging to achieve high-quality p-type material with good stability and reproducibility. Further research is needed to develop reliable and scalable methods for making p-type Ga2O3 and integrating it into power devices.

Nitrogen doping has also been explored as a potential method for achieving p-type conductivity in Ga2O3. Nitrogen is an acceptor dopant, which means it can introduce holes in the material when it substitutes for oxygen in the crystal lattice.

Several studies have reported successful nitrogen doping in Ga2O3, resulting in p-type behavior. For example, one study reported that nitrogen doping using plasma-assisted molecular beam epitaxy (MBE) could achieve p-type conductivity in Ga2O3 with a hole concentration of up to 10^17 cm^-3 and a hole mobility of 3 cm^2/Vs. Another study reported that nitrogen doping using ion implantation and annealing could achieve p-type conductivity with a hole concentration of up to 10^18 cm^-3.

However, the stability and reproducibility of nitrogen-doped Ga2O3 have not been well-established, and more research is needed to develop reliable and scalable methods for nitrogen doping in Ga2O3. Additionally, the use of nitrogen as a dopant in Ga2O3 can introduce defects and alter the material's properties, so careful optimization of the doping process is needed to minimize these effects. More discussion of semiconductor is here for green device concepts and basic about semiconductor devices.

What is multi-ferroic?Device target, Major challenges.

 Introduction:

What is multi-ferroelectric material?

A multi-ferroic material is a type of material that exhibits multiple types of ferroic ordering, such as ferromagnetism, ferroelectricity, and ferro-elasticity, in a single material. In other words, these materials can have more than one ferroic property simultaneously.

Ferroic materials are characterized by the existence of a spontaneous polarization or magnetization, which can be switched or reversed by an applied electric or magnetic field, respectively. Ferromagnetic materials, for example, exhibit a spontaneous magnetization, while ferroelectric materials exhibit a spontaneous electric polarization. Ferroelastic materials exhibit a spontaneous deformation or strain.

Multi-ferroic materials are of great interest because they offer the potential for new types of functional materials and devices, such as magnetoelectric sensors, actuators, and memory devices. For example, a magnetoelectric memory device could store data as both magnetic and electric signals, which could provide enhanced performance and energy efficiency compared to traditional memory technologies. How they are connected each other is shown in figure 1.

Figure 1: Connection of multiferroic phenomenon.

Some examples of multi-ferroic materials include bismuth ferrite (BiFeO3), which exhibits both ferroelectric and antiferromagnetic orderings, and lead magnesium niobate-lead titanate (PMN-PT), which exhibits both ferroelectric and ferroelastic orderings. Research is ongoing to explore new types of multi-ferroic materials and to understand the underlying physics that govern their behavior.

Ferroic in one materials?

materials can have both ferromagnetic and ferroelectric characteristics, and such materials are called "magnetoelectric multiferroics." These materials exhibit both magnetic and electric polarizations that are coupled to each other, allowing for control of one property with the other. The coupling between magnetic and electric polarizations in these materials can be exploited for various applications, including magnetoelectric sensors, actuators, and memory devices.

One example of a magnetoelectric multiferroic material is bismuth ferrite (BiFeO3), which exhibits both ferroelectric and antiferromagnetic orderings. Another example is TbMnO3, which exhibits ferromagnetism and ferroelectricity at low temperatures.

Magnetoelectric multiferroics are still an area of active research, and many challenges remain in developing practical devices based on these materials. One challenge is to optimize the coupling between the magnetic and electric polarizations, as this coupling can be weak in some materials. Another challenge is to develop methods for integrating these materials into practical devices with high performance and reliability. However, the potential applications of magnetoelectric multiferroics make them an exciting area of research with significant potential for technological innovation.

Device target and concepts:

Multi-ferroic materials are materials that exhibit both ferromagnetic and ferroelectric properties simultaneously. In other words, these materials possess magnetic and electric ordering that can be controlled by each other. The device concept of multi-ferroic materials involves the development of devices that exploit the unique properties of these materials for various applications.

One such application is in data storage devices, where multi-ferroic materials can be used to develop non-volatile memories. The electric field can be used to control the magnetic state of the material, leading to the possibility of developing magnetic random access memory (MRAM) devices with low power consumption and high speed and vice versa. Figure 2 shows a conceptual device with multiferroic concept. 

Figure 2: Magnetoelectric RAM concept of Multiferroic integration.

Another potential application is in sensors and actuators. Multi-ferroic materials can be used to develop sensors that can detect both magnetic and electric fields simultaneously, which can have applications in medical imaging and non-destructive testing. Additionally, multi-ferroic materials can also be used to develop actuators that can be controlled using either magnetic or electric fields, which can be useful in the development of microelectromechanical systems (MEMS).

Overall, the device concept of multi-ferroic materials has significant potential for various applications, including data storage, sensing, and actuation, and ongoing research in this area is expected to lead to the development of new and innovative devices.

Major challenges:

There are several major challenges associated with magnetoelectric multiferroic materials that are currently being addressed by researchers in the field. Some of these challenges include:

Finding new materials: Currently, there are only a limited number of materials that exhibit both ferromagnetic and ferroelectric properties, and most of these materials have low magnetoelectric coupling. Thus, one major challenge is to find new materials that exhibit strong magnetoelectric coupling and are suitable for practical applications.

Understanding the underlying physics: The physics of magnetoelectric coupling is still not well understood, and more research is needed to understand the mechanisms that govern the coupling between magnetic and electric properties.

Developing practical devices: Magnetoelectric multiferroic materials have the potential to enable new types of devices, such as magnetoelectric sensors, actuators, and memory devices. However, there are still significant challenges associated with developing practical devices based on these materials, such as achieving high sensitivity, reliability, and manufacturability.

Controlling domain structure: The domain structure of magnetoelectric multiferroic materials can have a significant impact on their properties and performance. However, controlling the domain structure of these materials is a significant challenge, and more research is needed to develop effective methods for controlling domain structure at the nanoscale.

Temperature effect: Temperature can have a significant effect on the properties of magnetoelectric multiferroic materials. The ferromagnetic and ferroelectric properties of these materials are often strongly coupled, and changes

Overall, magnetoelectric multiferroic materials are a promising area of research, but there are still many challenges that must be addressed before they can be effectively integrated into practical devices. Please find other fruitful discussion here.

MOSFET, MOSFET types and Applications

Introduction:

Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET) is a type of transistor used in electronic circuits to amplify or switch signals. This is consist of source, gate and drain. Operation of  MOSFET's is based on the interaction between a conducting channel and an applied electric field. 

Structure and operation:

Structure: MOSFETs are made up of a metal gate, a thin insulating layer of oxide (typically silicon dioxide), and a semiconductor channel. The channel is usually made of silicon, and the source and drain regions are doped to create a conducting path between them. When a voltage is applied to the gate, it creates an electric field that modifies the conductivity of the channel between the source and drain. If the gate voltage is higher than the threshold voltage, the MOSFET conducts, allowing current to flow through the channel. If the gate voltage is lower than the threshold voltage, the MOSFET does not conduct. Figure shows basic MOSFET structure.

Figure 1: Basic n- channel MOSFET structure

Figure 2 describes the detail operation principle and governing items.

Figure 2: Operation details of n-MOSFET

Electrical behavior if n-channel MOSFET shown in figure 3 where (a) transfer and  (b) on-off behaviors. The symbols have their usual meaning. Please follow some text book to understand the basic relation of them. This is the basic building block to acquire knowledge and understanding new materials system for MOSFET application.

Figure 3: for n-channel (a) transfer characteristic (b) ON-OFF behaviors 

Types: MOSFETs are available in two types: enhancement mode and depletion mode. In enhancement mode MOSFETs, the channel conductivity is enhanced by the gate voltage, while in depletion mode MOSFETs, the channel is already conducting, and the gate voltage reduces the conductivity.

Advantages: MOSFETs have several advantages over other types of transistors. They have high input impedance, which means that they require very little current to control the gate voltage. They also have low on-resistance, which means that they can handle high current without dissipating much power. MOSFETs also have high switching speeds and are commonly used in high-frequency applications.

Applications: 

MOSFETs are used in a variety of applications, including power electronics, digital circuits, amplifiers, and RF circuits. They are commonly used as switches to control the flow of current in electronic circuits. Please find more about semiconductor discussion here.

Techniques to extract MOS CAP parameters from C-V measurement.

Introduction: 

From the C-V measurement, we are able to extract the oxide thickness, flat and voltage, threshold voltage, effective oxide charges, and substrate doping concentration. The detailed techniques are discussed below:

Oxide thickness: 

From the measured C-V, and relation as shown in equation (1), we can estimate the oxide thickness is measured in the MOS structure. The Cox-accum is the strong accumulation capacitance value that is measured.

Figure 1: C-V curve 

Equation (1)

Flat capacitance and voltage:

In my previous discussion, I have clearly mentioned band bending and flat band, depletion conditions. It is difficult to get a flat band because all the surfaces have defects that are dangling bonds that create band bending so it is necessary the amount of bending in terms of voltage is effective for device operation considerations. Flat band condition in C-V measurement can be obtained. The gate voltage required to get a flat band is called flat band voltage(V_FB). The surface potential is zero in this condition because the band is flat. This voltage and its shift are widely used to judge device parameters, especially oxide charges. We can estimate flat band voltage through the C-V measurement of MOS CAP. First, flat band capacitance is calculated by oxide-capacitance and Debye length One important point is that the flat band capacitance is invalid if the interface trap is too large (over 10¹²). The C_ox means the value of the capacitance at a strong accumulation point. The Debye length is an indicator of the distance to which an electrical interaction can be sensed in the semiconductor. Once we know the flat band capacitance then from the position of the flat band capacitance, we can estimate the corresponding flat band voltage. By using equations (2) and (3) we can get the required information to estimate the flat band capacitance.

Equation (2)

Equation (3)

Effective oxide charge density:

The effective oxide charge (Qi) is a combination of fixed charge, oxide trapped charge, and mobile ionic charge. In C-V measurement, we cannot distinguish them. Temperature cycling can be a way to distinguish them. We only assume the charge is in between the semiconductor-oxide interface. Now, to estimate the flat effective oxide charge density simply calculate the difference of metal-semiconductor work function difference, and using equation (4) we have the relation of effective oxide charge. If we simply divide the charge by the electron’s charge (q) then we get the effective oxide-charge density. 

Equation (4)

Substrate doping concentration: Please check an example of it here. Please also find a detailed discussion about Magnetic phase transition, structural analysis, and crystallography understanding in the link.

Judge your MOS CAP C-V measurement conditions.

Introduction 

It is very important to judge mainly volatile or non-volatile metal-oxide-semiconductor field effect transistor (MOSFET) devices for the computer system. The purpose of MOSFET is to switch or retain memory information permanently. The C-V measurement is one of the strong techniques to judge the device’s quality. This is also useful to evaluate new materials as well. We can know useful information about doping density in the semiconductor, carrier lifetimes, oxide thickness, oxide charges, interface trap density, mobile ions, etc. Therefore, understanding the detail of C-V measurement is of prime interest.

Fundamentals of MOS capacitor

For the measurement, it is necessary to the fabricated device in the structure of the Metal/Oxide/Semiconductor/Metal structure. This is like a MOS capacitor as shown in figure 1. In the structure, the semiconductor and bottom metal electrode acts as cathode plate. The top metal on the insulator acts as another electrode (anode). This is complete like a typical capacitor structure. We simply determine the capacitance from C = A (K/d), where A is the area of the capacitor top electrode, K is the dielectric constant of the insulator, and d is the separation distance between the two electrodes. It is clearly seen from the relation that the larger the A and K, and the thinner the d then the higher the capacitance. Anyway, the semiconductor capacitance values range from nano-farads to pico-farads or smaller. C-V measurement concepts: Two ways we can measure the C-V. 1. Quasistatic 2. High frequency. 

Figure 1: Cross-sectional MOS cap structure and measurement configuration

Quasistatic condition 

This is corresponded to close equilibrium. By convention, the quasistatic C-V measurement is made by the sweeping bias voltage applied to the MOS capacitor resulting in the semiconductor surface changes from inversion to depletion and then to accumulation. In this process, the displacement current is measured as a function of time. The displacement current is the transient charging current of the MOS capacitor. Actually, there is no real current flowing through the oxide layer. This quasistatic measurement is useful when the oxide material is not leaky. If it is leaky conduction current will be added to the displacement current and measurements will be inaccurate. For high-quality oxide material, the leaky current is negligible. However, the good point is that modern computer-driven C-V measurement can correct the leakage current. Surely, the integration of charging current results in the measurement of the stored charge in the MOS capacitor. i.e., CV=Q. It is clear that, if the surface of the semiconductor is either in accumulation or inversion denotes the charged mobile carriers are just beneath the oxide. Finally, the maximum capacitance measured is nothing but the capacitance of the oxide layer alone Then, C_max= C_oxA, and A is the area of the gate electrode contact. On the other hand, if the semiconductor is depleted then there is no layer of mobile carriers underneath the oxide/semiconductor interface. The mobile carriers are present underneath the depletion region. Then, in the depletion, the measured C is consisting of the series combination of oxide and capacitance of the depletion region. This series combination means less than C_max. In the measurement, the voltage is swept from inversion to accumulation then capacitance decreases C_max towards minimum. Equation 1 shows the expected C_min relation.

The detailed behaviors are shown in figure 2. Here, x_o and K are the thickness and dielectric constant of the oxide material. X_d and K­_s are the maximum thickness and dielectric constant of the depletion layer (semiconductor part). A note to keep in mind is that there is an electrical charge are still existed within the depletion region due to doping of the semiconductor i.e ionized impurity atoms. The good point is that these ionized charges do not affect or contribute to the displacement current due to its static nature. But at a high temperature, they may move so care about temperature is essential. Usually, room temperature measurement does not affect them. 

Figure 2: Quasistatic C-V response ( p-type semiconductor) 

Earlier we discussed quasistatic measurements where the capacitance is directly measured by the integration of charging current. It requires the application of bias voltages across the capacitor with a superimposed AC signal (Figure 1). Typically, AC frequencies from 10 kHz to 10 MHz are considered for these measurements. The DC bias functions as sweep voltage that drive the capacitor from the accumulation region to the depletion region and goes into inversion as shown in figure 2 or the reverse way. Depending on the polarity of the DC bias and carrier type in the semiconductor the accumulation and depletion occur. The accumulated majority carrier near the surface of the semiconductor cannot pass through the insulator which results in a capacitance maximum in the accumulation region as shown in figure 3. 

Figure 3: High-frequency C-V (p-type semiconductor)

In this case, the capacitance measured under conditions of accumulation and depletion can be expected to be the same as observed in quasistatic measurements. If the frequency of the AC signal is high enough, then the capacitance measured under a condition of inversion is not the same as in the quasistatic case. The reason is the non-equilibrium behavior of the inversion layer. In the physical sense, the inversion layer should be formed from the minority carriers generated in the depletion region and swept to the surface by the electric field. From the bulk minority carriers also can diffuse. In simple understanding, the equilibrium conditions indicate that there is enough time for the inversion layer carrier concentration to respond to any changes in the applied field. In reality, if the semiconductor is good then the carrier generation -recombination processes occur slowly usually for silicon it is in the millisecond orders. So, if the applied AC voltage is in the MHz range, then the inversion layer responses very slowly to flow the signal and is similar to ionized dopant impurity atoms’ behaviors. Apparently, the inversion layer is fixed with the AC component. This behavior is shown in figure 3. The capacitance in the inversion layer is the series combination of oxide and depletion layer capacitance (fully depletion condition).

Deep depletion in C-V Measurements

We can measure capacitance versus voltage either by sweeping the applied voltage from accumulation to inversion (+ to - voltage for n-type; - to + for p-type) or inversion to accumulation. In the case of quasistatic measurements, the direction of the sweep makes essentially no difference in the C-V plot, because the MOS capacitor remains nearly at equilibrium. However, at high frequency, the C-V plot may differ in the inversion region depending on the direction and rate of the voltage sweep. This is due to the kinetics of the minority carrier generation as discussed earlier. If generation and recombination it takes a longer time (excellent substrate), then the inversion layer may not fully form during the fast switching from accumulation to inversion. This may increase the depletion layer than we expect for equilibrium conditions. We call this a deep depletion as mentioned in figure 4. 

Figure 4: Deep depletion sweep from accumulation to inversion

Such deep depletion should be avoided in conventional C-V measurement. Of course, we can take advantage of this situation to determine the time constant of carrier generation-recombination processes i.e minority carriers’ lifetime of the substrate. Anyway, at high frequency, we can find the onset of equilibrium behavior, i.e., MOS capacitance increases in inversion. The minority carrier lifetime can be estimated by determining the dependence of inversion capacitance on sweep rate. The derivative of this function extrapolated back to equilibrium conditions is the minority carrier lifetime. 

Practically high-frequency C-V measurements are nearly always made by sweeping the applied bias voltage from inversion to accumulation to eliminate deep depletion. A point to be noted is that by proper biasing and illumination of the surface the substrate surface is fully inverted for inversion layer formation by illumination. Of course, the sweep should be done without illumination. Of course, the voltage sweep itself should be made without illumination. The ideal MOS capacitance per unit area, C, follows equation 1. Finally, if the substrate doping is constant, an increase in oxide thickness reduces the capacitance of the oxide layer resulting in a reduction of MOS capacitance. Furthermore, the position of the depletion region as a function of bias moves to higher values of voltage magnitude so a higher voltage magnitude must be applied across a thicker oxide to obtain the same electric field magnitude at the oxide/semiconductor interface. Also, if oxide thickness is fixed but substrate doping causes a corresponding change in the depletion layer capacitance. This is well understood that increasing (or decreasing) substrate doping causes the maximum width of the depletion layer to be reduced (or increased). So, at fixed oxide thickness, the Cox remains fixed, but the Cmin varies with substrate doping. Please find information to be extracted from the C-V measurement. You may also have an interest in band bending and p-n junction detail. Please check also them.