AlGaN/GaN heterostructures on insulating AlGaN nucleation layers

Abstract

A single temperature process using AlGaN nucleation layers has been developed that produces device-quality, GaN-based materials with bilayer step surfaces. The AlGaN nucleation layer is deposited by flow modulation organometallic vapor phase epitaxy at temperatures in excess of 1000 °C, where GaN and AlGaN films can be subsequently grown. We have optimized this process on both sapphire and SiC substrates, where the conditions for nucleation are found to be quite different. For growth on SiC, aluminum mole fractions ranging from 6% to 35% result in featureless surfaces. Optimizing the alloy composition and thickness of the nucleation layer on SiC allows the deposition of GaN buffer layers exceeding 5 μm without the formation of cracks. A minimum of 15% aluminum in the nucleation layer is required for smooth growth on sapphire substrates. High room temperature two-dimensional electron gas mobilities of 1575 and 1505 cm2/Vs with sheet charge densities of 1.0×1013 and 1.4×1013 cm−2 are observed in undoped AlGaN/GaN structures placed on insulating AlGaN nucleation layers on sapphire and SiC, respectively.

Role of Spontaneous and Piezoelectric Polarization Induced Effects in Group-III Nitride Based Heterostructures and Devices

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Tunneling effects and intersubband absorption in AlN/GaN superlattices

“…1; this lifts the Fermi energy and results instantly in a negative voltage at this contact. 18 This voltage becomes larger if the lateral conductivity in the wells is low and vice versa; and the latter is strongly influenced by parasitic effects due to midgap states. Since the spectrometer's white light source is filtered only by the ZnSe window of the cryostat, photon energies up to 2.5 eV are available.…”

Results, Potential and Challenges of High Power GaN-Based Transistors

“…A thin AlGaN nucleation layer is first grown, followed by %1 mm thick GaN buffer/channel layer, followed in turn by a %300 # e thick pseudomorphic Al 0X3 Ga 0X7 N barrier layer [2]. The density of the 2DEG in this design is 1 Â 10 13 /cm 2 and can be raised by using selective silicon doping of the barrier.…”