III-V Nitride Semiconductors Research Articles

Effects of X-ray and γ-ray Irradiation on GaN

ABSTRACTAs part of the feasibility study of using III-V nitride semiconductors for x-ray and γ-ray detection, the irradiation effects on GaN were investigated. GaN films with very different electrical resistivity and electron concentration were used in the study. The electron mobility, photoconductivity spectra, and photo-luminescence spectra were measured before and after irradiation. An enhanced ημτ product for undoped GaN films and an enhanced blue luminescence for a Zn-doped sample were observed after irradiation.

Electronic Structures of Wurtzite GaN, InN and Their Alloy Ga1-xInxN Calculated by the Tight-Binding Method

The semi-empirical tight-binding method is used to investigate band structures of wurtzite III-V nitride semiconductors. The tight-binding band structures of GaN and InN are first obtained by fitting the data to experiments and more accurate calculations. To obtain better description of the band structures, second-nearest-neighbor s and p state interactions are included and Ga 3d and In 4d electrons are treated as band states. Then, the band structure of the alloy Ga1-x Inx N is predicted based on the obtained tight-binding parameters and a pseudobinary alloy model. The predicted alloy band gaps are in good agreement with experimental ones. The electron effective masses of the alloy are also presented. The effects of the second-nearest-neighbor interactions and nearest-neighbor s-d and p-d state interactions on the band structures are discussed in detail.

Large-band-gap SiC, III-V nitride, and II-VI ZnSe-based semiconductor device technologies

In the past several years, research in each of the wide-band-gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high-temperature electronics and short-wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high-power operation. The present advanced stage of development of SiC substrates and metal-oxide-semiconductor technology makes SiC the leading contender for high-temperature and high-power applications if ohmic contacts and interface-state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high-temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light-emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN-based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short-wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN-based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe-based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide-band-gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Preparation and properties of III-V nitride thin films

Thin films of III-V nitride semiconductors (AlN, GaN, InN), mixed-crystalline films (AlxIn1−xN), and multilayered films (GaN/InN)n were grown by rf magnetron sputtering at low substrate temperatures below 500 °C. These films were characterized by x-ray diffraction, Raman scattering, optical absorption, and electrical measurements; it was proved that they have high crystal quality comparable to the previously reported data obtained by other growth methods. Dependence of the band-gap energy of AlxIn1−xN on composition x was determined. Multilayered films of (GaN/InN) were prepared for the first time; these films showed the characteristic diffusion property to make an ordered-alloy superlattice.