B. Sverdlov

Bio: B. Sverdlov is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Wurtzite crystal structure & Molecular beam epitaxy. The author has an hindex of 18, co-authored 27 publications receiving 3551 citations. Previous affiliations of B. Sverdlov include Urbana University.

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

Abstract: 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.

Formation of threading defects in GaN wurtzite films grown on nonisomorphic substrates

Abstract: Possible causes of a dense network of threading defects in epitaxial hexagonal GaN films grown on various substrates are discussed. We show that these defects originate at the substrate/film interface as the boundaries between differently stacked hexagonal domains, and are created by surface steps on substrates nonisomorphic with wurtzite GaN. We argue that these defects are inherent in the epitaxy of wurtzite films on nonisomorphic substrates. As a result, isomorphic substrates such as ZnO and GaN should be explored for wurtzite nitride growth. Possible effects of these defects on the properties of wurtzite nitrides are briefly discussed.

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.

Mechanisms of band‐edge emission in Mg‐doped p‐type GaN

Abstract: Time‐resolved photoluminescence has been employed to study the mechanisms of band‐edge emissions in Mg‐doped p‐type GaN. Two emission lines at about 290 and 550 meV below the band gap (Eg) have been observed. Their recombination lifetimes, dependencies on excitation intensity, and decay kinetics have demonstrated that the line at 290 meV below Eg is due to the conduction band‐to‐impurity transition involving shallow Mg impurities, while the line at 550 meV below Eg is due to the conduction band‐to‐impurity transition involving doping related deep‐level centers (or complexes).

Time-resolved Raman studies of the decay of the longitudinal optical phonons in wurtzite GaN

Abstract: Decay of the longitudinal-optical (LO) phonons in wurtzite GaN has been studied by subpicosecond time-resolved Raman spectroscopy. Our experimental results show that among the various possible decay channels, the LO phonons in wurtzite GaN decay primarily into a large wave-vector TO and a large wave-vector LA or TA phonon. These experimental results are consistent with the recent theoretical calculations of the phonon dispersion curves for wurtzite GaN.Decay of the longitudinal-optical (LO) phonons in wurtzite GaN has been studied by subpicosecond time-resolved Raman spectroscopy. Our experimental results show that among the various possible decay channels, the LO phonons in wurtzite GaN decay primarily into a large wave-vector TO and a large wave-vector LA or TA phonon. These experimental results are consistent with the recent theoretical calculations of the phonon dispersion curves for wurtzite GaN.

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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. ...

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

Optically pumped lasing of ZnO at room temperature

Abstract: We report the observation of optically pumped lasing in ZnO at room temperature. Thin films of ZnO were grown by plasma-enhanced molecular beam epitaxy on (0001) sapphire substrates. Laser cavities formed by cleaving were found to lase at a threshold excitation intensity of 240 kW cm−2. We believe these results demonstrate the high quality of ZnO epilayers grown by molecular beam epitaxy while clearly demonstrating the viability of ZnO based light emitting devices.

InGaN-Based Multi-Quantum-Well-Structure Laser Diodes.

Abstract: InGaN multi-quantum-well (MQW) structure laser diodes (LDs) fabricated from III-V nitride materials were grown by metalorganic chemical vapor deposition on sapphire substrates. The mirror facet for a laser cavity was formed by etching of III-V nitride films without cleaving. As an active layer, the InGaN MQW structure was used. The InGaN MQW LDs produced 215 mW at a forward current of 2.3 A, with a sharp peak of light output at 417 nm that had a full width at half-maximum of 1.6 nm under the pulsed current injection at room temperature. The laser threshold current density was 4 kA/cm2. The emission wavelength is the shortest one ever generated by a semiconductor laser diode.