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The polarization difference and band offset between Al(Ga)N and GaN induce two-dimensional (2D) free carriers in Al(Ga)N/GaN heterojunctions without any chemical doping. A high-density 2D electron gas (2DEG), analogous to the recently discovered 2D hole gas in a metal-polar structure, is predicted in a N-polar pseudomorphic GaN/Al(Ga)N heterostructure on unstrained AlN. We report the observation of such 2DEGs in N-polar undoped pseudomorphic GaN/AlGaN heterostructures on single-crystal AlN substrates by molecular beam epitaxy. With a high electron density of ∼4.3 ×1013/cm2 that maintains down to cryogenic temperatures and a room temperature electron mobility of ∼450 cm2/V s, a sheet resistance as low as ∼320 Ω/◻ is achieved in a structure with an 8 nm GaN layer. These results indicate significant potential of AlN platform for future high-power RF electronics based on N-polar III-nitride high electron mobility transistors.
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Abstract Harnessing resonant tunneling transport in III-nitride semiconductors to boost the operating frequencies of electronic and photonic devices, requires a thorough understanding of the mechanisms that limit coherent tunneling injection. Towards this goal, we present a concerted experimental and theoretical study that elucidates the impact of the collector doping setback on the quantum transport characteristics of GaN/AlN resonant tunneling diodes (RTDs). Employing our analytical model for polar RTDs, we quantify the width of the resonant-tunneling line shape, demonstrating that the setback helps preserve coherent injection. This design results in consistently higher peak-to-valley-current ratios (PVCRs), obtaining a maximum PVCR = 2.01 at cryogenic temperatures.more » « less
