A. Botchkarev

Bio: A. Botchkarev is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Molecular beam epitaxy & Wurtzite crystal structure. The author has an hindex of 23, co-authored 48 publications receiving 2956 citations. Previous affiliations of A. Botchkarev include Urbana University.

Valence‐band discontinuities of wurtzite GaN, AlN, and InN heterojunctions measured by x‐ray photoemission spectroscopy

Abstract: The valence‐band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x‐ray photoemission spectroscopy. A significant forward–backward asymmetry was observed in the InN/GaN–GaN/InN and InN/AlN–AlN/InN heterojunctions. The asymmetry was understood as a piezoelectric strain effect. We report the valence band discontinuities for InN/GaN=1.05±0.25 eV, GaN/AlN=0.70±0.24 eV, and InN/AlN=1.81±0.20 eV, all in the standard type I lineup. These values obey transitivity to within the experimental accuracy. Tables of photoemission core level binding energies are reported for wurtzite GaN, AlN, and InN.

Very low resistance multilayer Ohmic contact to n‐GaN

Abstract: A new metallization scheme has been developed for obtaining very low Ohmic contact to n‐GaN. The metallization technique involves the deposition of a composite metal layer Ti/Al/Ni/Au (150 A/2200 A/400 A/500 A) on n‐GaN preceded by a reactive ion etching (RIE) process which most likely renders the surface highly n type. Of the several attempts and with annealing at 900 °C for 30 s, contacts with specific resistivity values of ρs=8.9×10−8 Ω cm2 or lower for a doping level of 4×1017 cm−3 were obtained. The physical mechanism underlying the realization of such a low resistivity is elucidated.

Microstructure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts for n-GaN

Abstract: Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts on n‐type GaN (∼1017 cm−3) epitaxial layers. The metals were deposited either by conventional electron‐beam or thermal evaporation techniques, and then thermally annealed at 900 °C for 30 s in a N2 atmosphere. Before metal deposition, the GaN surface was treated by reactive ion etching. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112]TiN//[10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact.

Valence-band discontinuity between GaN and AlN measured by x-ray photoemission spectroscopy

Abstract: The valence‐band discontinuity at a wurtzite GaN/AlN(0001) heterojunction is measured by x‐ray photoemission spectroscopy. The method first measures the core level binding energies with respect to the valence‐band maximum in both GaN and AlN bulk films. The precise location of the valence‐band maximum is determined by aligning prominent features in the valence‐band spectrum with calculated densities of states. Tables of core level binding energies relative to the valence‐band maximum are reported for both GaN and AlN. Subsequent measurements of separations between Ga and Al core levels for thin overlayers of GaN film grown on AlN and vice versa yield a valence‐band discontinuity of ΔEV=0.8±0.3 eV in the standard type I heterojunction alignment.

High transconductance normally-off GaN MODFETs

Abstract: Normally-off GaN based modulation doped field-effect transistors have been fabricated. The extrinsic transconductance of MODFETs with gate and channel lengths of 3 and 5 /spl mu/m, respectively, is as high as 120 mS/mm. The devices exhibit 300 mA/mm current at a positive gate bias of 3 V. This transconductance value compares very favourably with the 45 mS/mm and 24 mS/mm reported earlier for 1 and 0.23 /spl mu/m gate devices, respectively.

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures

Abstract: Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15

First-principles calculations for defects and impurities: Applications to III-nitrides

Abstract: First-principles calculations have evolved from mere aids in explaining and supporting experiments to powerful tools for predicting new materials and their properties. In the first part of this review we describe the state-of-the-art computational methodology for calculating the structure and energetics of point defects and impurities in semiconductors. We will pay particular attention to computational aspects which are unique to defects or impurities, such as how to deal with charge states and how to describe and interpret transition levels. In the second part of the review we will illustrate these capabilities with examples for defects and impurities in nitride semiconductors. Point defects have traditionally been considered to play a major role in wide-band-gap semiconductors, and first-principles calculations have been particularly helpful in elucidating the issues. Specifically, calculations have shown that the unintentional n-type conductivity that has often been observed in as-grown GaN cannot be a...

Band parameters for nitrogen-containing semiconductors

Abstract: We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...