Wide Energy Gap Semiconductors Research Articles

Two-dimensional heterostars from nanographene and group-III nitrides for efficient spin filters: Spintronic and quantum transport properties

Two-dimensional (2D) heterostructures open the door toward novel applications, such as multiterminal transistors, by integrating the properties of the participant materials. Here we construct 2D heterostars from zigzag-triangular graphene (ZTG) and group-III nitrides. They are investigated using density functional theory and non-equilibrium Green’s function approaches. These heterostars are ferromagnetically spin-ordered devices that originate and distribute on ZTG. Further control over the net spin can be achieved by forming bilayer heterostars where spin can be increased, decreased, or removed. Single-layer heterostars are wide energy gap semiconductors of ∼3.5 eV that decrease to ∼1 eV in bilayers or are kept unchanged in other bilayers. Quantum transport calculations show that different spintronic devices can be constructed by connecting the source/drain voltage to different terminals of the nanostars. These devices are characterized by a low tunneling current through the potential barrier of group-III nitrides that significantly increased by applying gate voltage. A spin filter based on graphene-AlN nanostar with efficient separation of spin-up current is demonstrated. Also, a significant improvement in both the spin-up and spin-down currents can be achieved in the same nanostar but using other terminals. 2D heterostars are then potential candidates for building multi-terminal spintronic devices.

Electron transport within the wurtzite and zinc-blende phases of gallium nitride and indium nitride

Wide energy gap semiconductors are broadly recognized as promising materials for novel electronic and opto-electronic device applications. As informed device design requires a firm grasp on the material properties of the underlying electronic materials, the electron transport that occurs within the wide energy gap semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving and burgeoning field of research, we review analyzes of the electron transport within some wide energy gap semiconductors of current interest in this paper. In order to narrow the scope of this review, we will primarily focus on the electron transport that occurs within the wurtzite and zinc-blende phases of gallium nitride and indium nitride in this review, these materials being of great current interest to the wide energy gap semiconductor community; indium nitride, while not a wide energy gap semiconductor in of itself, is included as it is often alloyed with other wide energy gap semiconductors, the resultant alloy often being a wide energy gap semiconductor itself. The electron transport that occurs within zinc-blende gallium arsenide will also be considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, will also be provided. Steady-state and transient electron transport results are presented. The evolution of the field, a survey of the current literature, and some applications for the results presented herein, will also be featured. We conclude our review by presenting some recent developments on the electron transport within these materials. This review is the latest in a series of reviews that have been published on the electron transport processes that occur within the class of wide energy semiconductor materials. The results and references have been updated to include the latest developments in this rapidly evolving field of study.

Recent Advancement in Charge and Photo-Assisted Non-Contact Electrical Characterization of SiC, GaN, and AlGaN/GaN HEMT

The charge-based corona-Kelvin noncontact metrology, originally developed for Si IC fabrication, has recently been extended to wide energy gap semiconductors. We discuss principles of this extension and key applications, namely: high precision dopant measurement on SiC and GaN; two-dimensional electron gas characterization in AlGaN/GaN HEMT structures; interface and dielectric characterization on epi-layers with SiO2, SiN and Al2O3; comprehensive interfacial instability characterization of oxidized SiC; and whole wafer mapping of defects with a charge-assisted surface voltage technique. This powerful set of measurements is performed without fabrication of any test structures or electrical contact. Corresponding commercial tools are currently being introduced. Based on the historical example of silicon IC, we believe that this approach shall offer enhanced testing for research and for manufacturing process control with reduced cost and fast data feedback benefiting the wide-bandgap device technology.

Surface photovoltage inversion and photocatalytic properties of PbI2 microcrystals under sub-bandgap illumination

Surface photovoltage inversion was found in PbI2 microcrystals, manifested as a significant increase in the absolute value of surface barrier height under sub-bandgap illumination. The corresponding surface states located at 0.43 eV above the valence band was detected, and the magnitude of photovoltage inversion was found to increase with increasing applied field strength. Besides, transient surface photovoltage responses and the time constants of the relaxation showed a dependence on the wavelength of illumination. When irradiated with 518–632 nm, the exciton together with the lead ion vacancy caused the population of holes in the surface state; while under 700-nm light irradiation, holes depopulation occurred on the surface. Transient surface photovoltage results show that the relaxation of the sub-bandgap surface photovoltage is exponential with long time constant. The different charge transportation processes agree well with the photocatalytic degradation of MO experiments under different wavelength irradiation. It is revealed that the exciton and the surface states could significantly affect the movement of photogenerated charge carriers, which lead to different degradation results of MO. These findings demonstrate a model involving photostimulated population of surface states for the study of surfaces of wide energy gap semiconductors, which shows the highly selective control of photogenerated charge carriers’ behaviors by tuning the wavelength of irradiation.

Review—Recent Advancement in Charge- and Photo-Assisted Non-Contact Electrical Characterization of SiC, GaN, and AlGaN/GaN HEMT

The charge-based corona-Kelvin non-contact metrology, originally developed for Si IC fabrication, has recently been extended to wide energy gap semiconductors. We discuss principles of this extension and key applications, namely: high precision dopant measurement on SiC and GaN; two-dimensional electron gas characterization in AlGaN/GaN HEMT structures; interface and dielectric characterization on epi-layers with SiO2 and SiN; comprehensive interfacial instability characterization of oxidized SiC; and whole wafer mapping of defects with a charge-assisted surface voltage technique, QUAD. This powerful set of measurements is performed without fabrication of any test structures or electrical contact. Corresponding commercial tools are currently being introduced. Based on the historical example of silicon IC, we believe that this approach shall offer enhanced testing for research and for manufacturing process control with reduced cost and fast data feedback benefiting wide-bandgap device technology.

A 2015 perspective on the nature of the steady-state and transient electron transport within the wurtzite phases of gallium nitride, aluminum nitride, indium nitride, and zinc oxide: a critical and retrospective review

Wide energy gap semiconductors are broadly recognized as promising materials for novel electronic and optoelectronic device applications. As informed device design requires a firm grasp of the material properties of the underlying electronic materials, the electron transport that occurs within the wide energy gap semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving and burgeoning field of research, we review analyzes of the electron transport within some wide energy gap semiconductors of current interest in this paper. In order to narrow the scope of this review, we will primarily focus on the electron transport that occurs within the wurtzite phases of gallium nitride, aluminum nitride, indium nitride, and zinc oxide in this review, these materials being of great current interest to the wide energy gap semiconductor community; indium nitride, while not a wide energy gap semiconductor in of itself, is included as it is often alloyed with other wide energy gap semiconductors, the resultant alloys being wide energy gap semiconductors themselves. The electron transport that occurs within zinc-blende gallium arsenide is also considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, is also provided. Steady-state and transient electron transport results are presented. The evolution of the field, and a survey of the current literature, are also featured. We conclude our review by presenting some recent developments on the electron transport within these materials.

Optical properties of aluminum-doped zinc oxide films deposited by direct-current pulse magnetron reactive sputtering

A series of 〈103〉-oriented aluminum-doped zinc oxide (AZO) films were deposited on glass substrates via direct-current pulse magnetron reactive sputtering at different O2-to-Ar gas flow ratios (GFRs). The optical properties of the films were characterized using the fitted optical constants in the general oscillator model (which contains two Psemi-Tri oscillators) through the use of measured ellipsometric parameters. The refractive index dispersion data below the interband absorption edge were analyzed using a single-oscillator model. The fitted optical energy gap obtained using the single-oscillator model clearly shows a blue shift, followed by a red shift, as the GFR increases from 0.9/18 to 2.1/18. This shift can be attributed to the change in the free electron concentration of the film, which is closely related to the film stress. In addition, the fitted β value indicates that the AZO film falls under the ionic class. The photoluminescence spectrum indicates a photoluminescence mechanism of the direct and wide energy gap semiconductor.

PROGRESS IN SIC MATERIALS/DEVICES AND THEIR COMPETITION

Power semiconductor devices are important for numerous applications with power conversion being an important one. Wide energy gap semiconductors SiC and GaN have properties that make them attractive for such applications. Among these properties are high thermal conductivity, high breakdown electric field, wide energy gap, low intrinsic carrier concentration, high thermal stability, high saturation velocity and chemical inertness. These lead to low on-resistance, high breakdown voltage, high frequencies, small volume, and small passive inductors and capacitors. These desirable properties are offset by the higher material costs and higher defect densities. Although wide energy gap devices have been in development for many years, only recently have they become available commercially. Their main competition is silicon power devices with breakdown voltages up to 8000 V and very high surge current capacity. However, silicon power devices are approaching their material limits and wide energy gap devices are beginning to have an impact in the power electronics space. SiC has the advantage of substrates with diameters approaching 150 mm and the ability to grow thermal SiO2 . GaN has the heterojunction advantage, but no viable substrate technology. In fact, a large portion of SiC production is used for GaN substrates. GaN material development has also benefited significantly from the development of optical devices, e.g., light-emitting diodes and lasers.

Memory effects in CVD diamond

CVD diamond, as other wide energy gap semiconductors or insulators, is known to present polarization effects when used as a nuclear particle detector, which are due to the building up of an internal space-charge electric field and are responsible for “memory” effects if the polarization is not erased. Polarization effects are larger when the thickness of the sample is longer than the drift length of carriers and give rise to a shortening of the electric field region inside the sample. In this work, IBIC (Ion Beam Induced Charge) measurements with 1 and 2 MeV proton beams have been carried out on a relatively thin CVD diamond sample with the conclusion that no memory or hysteresis effects were present even by switching from one polarity to the opposite one in subsequent measurements. However, it resulted that the values of the charge collection efficiency (cce) did depend on counting rate and the lowering at large counting rates was attributed to a local polarization due to trapping. Finally, in some cases cce turned out to be larger than 1, a result which could be either due to local detrapping or to non-blocking contacts.

NO<sub>2</sub>无Doppler增宽的磁场调制激光光谱

As a wide energy gap semiconductor, diamond is expected to play a role in UV light-emitting diode or laser. However, the impurities and vacancies in diamond exert a great influence on optical properties of the crystals. It is important, therefore, to study the relation between impurities and the optical properties, and furthermore, to study the control of the impurities.

ZnSe-ZnSxSe1−x and ZnSe-Zn1−xMnxSe metal-insulator-semiconductor heterostructure lasers

Metal-insulator-semiconductors (MIS) heterostructures, using ZnSe and ZnSe-based ternary compounds such as ZnSSe and ZnMnSe, have been proposed to obtain efficient blue light emission and lasing action. MIS laser structures are particularly desirable for wide energy gap semiconductors in which the controlled doping of n- and p-type impurities is somewhat difficult to realize. The MIS heterostructure laser is a novel device as an alternative to the conventional p-n double heterojunction laser. In these lasers, efficient minority carrier injection in the active layer is achieved from the MIS interface in place of a p-n heterojunstion emitter. Emitted photons are confined in the active layer as they are reflected by a heterostructure dielectric discontinuity (e.g., ZnSe-ZnSxSe1-x) on one side and the perfectly reflecting surface of the barrier metal on the other. Modal analysis of a stripe geometry Au-SiO2-n-ZnSe-n-ZnSxSe1-x-n-ZnSe MIS laser is presented. The output characteristics are compared with a conventional p-n double heterostructure laser. A MIS heterostructure to realize a distributed feedback laser is also discussed.