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

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

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.

Band parameters for III–V compound semiconductors and their alloys

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<x<0.5) and thickness between 20 and 65 nm demonstrate the important role of spontaneous and piezoelectric polarization on the carrier confinement at GaN/AlGaN and AlGaN/GaN interfaces. Characterization of the electrical properties of nominally undoped transistor structures reveals the presence of high sheet carrier concentrations, increasing from 6×1012 to 2×1013 cm−2 in the GaN channel with increasing Al-concentration from x=0.15 to 0.31. The observed high sheet carrier concentrations and strong confinement at specific interfaces of the N- and Ga-face pseudomorphic grown heterostructures can be explained as a consequence of interface charges induced by ...

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

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...

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

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...

Band parameters for nitrogen-containing semiconductors

In this letter we report the fabrication and dc characterization of a high electron mobility transistor (HEMT) based on a n‐GaN‐Al0.14Ga0.86N heterojunction. The conduction in our low pressure metalorganic chemical vapor deposited heterostructure is dominated by two‐dimensional electron gas at the heterostructure interface. HEMT devices were fabricated on ion‐implant isolated mesas using Ti/Au for the source drain ohmic and TiW for the gate Schottky. For a device with a 4 μm gate length (10 μm channel opening, i.e., source‐drain separation), a transconductance of 28 mS/mm at 300 K and 46 mS/mm at 77 K was obtained at +0.5 V gate bias. Complete pinchoff was observed for a −6 V gate bias.

High electron mobility transistor based on a GaN‐AlxGa1−xN heterojunction

The need for efficient, compact and robust solid-state UV optical sources and sensors had stimulated the development of optical devices based on III–nitride material system. Rapid progress in material growth, device fabrication and packaging enabled demonstration of high efficiency visible-blind and solar-blind photodetectors, deep-UV light-emitting diodes with emission from 400 to 250 nm, and UV laser diodes with operation wavelengths ranging from 340 to 350 nm. Applications of these UV optical devices include flame sensing; fluorescence-based biochemical sensing; covert communications; air, water and food purification and disinfection; and biomedical instrumentation. This paper provides a review of recent advances in the development of UV optical devices. Performance of state-of-the-art devices as well as future prospects and challenges are discussed.

https://iopscience.iop.org/article/10.1143/JJAP.44.7191/pdf

III-Nitride UV Devices

We present an experimental and theoretical study of nonresonant detection of subterahertz radiation in GaAs/AlGaAs and GaN/AlGaN heterostructure field effect transistors. The experiments were performed in a wide range of temperatures (8–300 K) and for frequencies ranging from 100 to 600 GHz. The photoresponse measured as a function of the gate voltage exhibited a maximum near the threshold voltage. The results were interpreted using a theoretical model that shows that the maximum in photoresponse can be explained by the combined effect of exponential decrease of the electron density and the gate leakage current.

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Nonresonant Detection of Terahertz Radiation in Field Effect Transistors

We report on the fabrication and characterization of photoconductive ultraviolet detectors based on insulating single‐crystal GaN. The active layer (GaN) was deposited over basal‐plane sapphire substrates using a unique switched atomic‐layer‐epitaxy process. The sensors were measured to have a responsivity of 2000 A/W at a wavelength of 365 nm under a 5‐V bias. The responsivity remained nearly constant for wavelengths from 200 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 375 nm). We estimate our sensors to have a gain of 6×103 (for wavelength 365 nm) and a bandwidth in excess of 2 kHz. The photosignal exhibited a linear behavior over five orders of incident optical power, thereby implying a very large dynamic range for these GaN‐based ultraviolet sensors.

High-responsivity photoconductive ultraviolet sensors based on insulating single-crystal GaN epilayers

We report on AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOS-HFETs) grown over insulating 4H–SiC substrates. We demonstrate that the dc and microwave performance of the MOS-HFETs is superior to that of conventional AlGaN/GaN HFETs, which points to the high quality of SiO2/AlGaN heterointerface. The MOS-HFETs could operate at positive gate biases as high as +10 V that doubles the channel current as compared to conventional AlGaN/GaN HFETs of a similar design. The gate leakage current was more than six orders of magnitude smaller than that for the conventional AlGaN/GaN HFETs. The MOS-HFETs exhibited stable operation at elevated temperatures up to 300 °C with excellent pinch-off characteristics. These results clearly establish the potential of using AlGaN/GaN MOS-HFET approach for high power microwave and switching devices.

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M. Asif Khan

Papers

High electron mobility transistor based on a GaN‐AlxGa1−xN heterojunction

III-Nitride UV Devices

Nonresonant Detection of Terahertz Radiation in Field Effect Transistors

High-responsivity photoconductive ultraviolet sensors based on insulating single-crystal GaN epilayers

AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors on SiC substrates