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In this letter, we report the band offset characterization of the atomic layer deposited aluminum oxide on non-polar m-plane indium nitride grown by plasma-assisted molecular beam epitaxy by using x-ray photoelectron spectroscopy. The valence band offset between aluminum oxide and m-plane indium nitride was determined to be 2.83 eV. The Fermi level of indium nitride was 0.63 eV above valence band maximum, indicated a reduced band bending in comparison to polar indium nitride. The band gap of aluminum oxide was found to be to 6.7 eV, which gave a conduction band offset of 3.17 eV. [ABSTRACT FROM AUTHOR]

A comparative assessment of AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy on silicon and sapphire substrates has been carried out. Large-area power GaN HEMTs with identical device dimensions were fabricated on both substrates. A thicker AlN buffer layer was used for the GaN HEMT on silicon to achieve similar quality and uniformity of GaN epitaxy for rational comparison with that grown on sapphire. Direct-current analysis and physical characterization were carried out to understand the performance of the devices. Mathematical measurement of the instability of the current-voltage ( I- V) characteristic at high applied drain bias was carried out to evaluate the performance of both devices. An improved two-dimensional (2D) analysis of the I- V characteristic was performed from a thermal perspective including appropriate scattering effects on the 2D electron gas mobility. The experimental and analytical studies were correlated to reveal the effects of temperature-sensitive scattering phenomena on the mobility as well as on the I- V characteristic at high drain bias in terms of lattice thermal heating. It is observed that the HEMT on Si has improved stability compared with sapphire due to its weaker scattering phenomena at high drain bias, associated with its thermal conductivity. Simulation of 2D thermal mapping was also carried out to distinguish the hot-spot regions of the devices. The comparable electrical performance of these devices illustrates the viability of AlGaN/GaN HEMTs on Si(111) to achieve low-cost stable devices with better thermal power handling for high-voltage applications. [ABSTRACT FROM AUTHOR]

Electrical photoelectrical, and microcathodoluminescence properties were measured on doped p-GaN superlattices prepared by molecular beam epitaxy on c-plane sapphire substrates. The photosensitivity of such superlattices is at least two orders of magnitude higher and the microcathodoluminescence intensity is about five times lower than for similarly grown uniformly doped p-GaN films. The difference is explained by the spatial separation of the photoexcited electrons and holes by the superlattice potential. The sheet carrier concentration in the superlattice is shown to be several times (6.6×1012 cm-2 vs 2×1013 cm-2) lower and the effective hole mobility almost two times higher (20 cm2/V s vs 12 cm2/V s) than for bulk p-GaN samples with similar doping. [ABSTRACT FROM AUTHOR]

Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn1-xCdxO alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the trend Eg(x)=3.37-2.82x+0.95x2. Incorporation of Cd was also shown to somewhat slow down thermal variation of the band gap energies, beneficial for future device applications. [ABSTRACT FROM AUTHOR]

A comparison is reported of the electrical, photoelectrical, and microcathodoluminescence properties of bulk p-GaN films and p-type p-GaN(Mg)/GaN superlattices grown by molecular beam epitaxy. It is shown that the microcathodoluminescence intensity is much lower and the photocurrent (both on samples with indium Ohmic contacts and on Au Schottky diodes) much higher for the doped superlattices due to the spatial separation of photoexcited electrons and holes in the doped and undoped layers and corresponding increase of the lifetime in comparison to the bulk samples. The in-plane conductivity in the doped superlattices is not enhanced significantly relative to conventional p-GaN, but the hole mobilities are increased (from 12 to 20 cm²/V s). [ABSTRACT FROM AUTHOR]

Multiple AlGaN/GaN heterostructure has been grown on Si(111) substrate by molecular beam epitaxy with different buffer growth conditions. Its influence on physical and electrical properties of two-dimensional electron gas (2DEG) has been investigated. Correlation between growth temperature variation in AlN intermediate layer and thick GaN buffer layer on 2DEG transport property has been observed. Besides the variation in growth temperatures, dissimilar partial doping in the thick GaN buffer has also been studied. Impact of different silicon substrate doping has been examined to inspect the electrical properties of high electron mobility transistors (HEMT). DC characteristics of large area fabricated HEMT have been compared in terms of current, transconductance, and linearity for power amplifier applications. [ABSTRACT FROM AUTHOR]