Very High Density (> 10(14) cm(-2)) Polarization-Induced 2D Hole Gases Observed in Undoped Pseudomorphic InGaN/AlN Heterostructures

High hole densities are desired in p-channel field effect transistors to improve the speed and on-currents. Building on the recently discovered undoped, polarization-induced GaN/AlN 2D hole gas (2DHG), this work demonstrates the tuning of the piezoelectric polarization difference across the heterointerface by introducing indium in the GaN channel. Using careful design and epitaxial growths, these pseudomorphic (In)GaN/AlN heterostructures result in some of the highest carrier densities of >10(14) cm(-2) in a III-nitride heterostructure-just an order below the intrinsic crystal limit of approximate to 10(15) cm(-2). These ultra-high density InGaN/AlN 2DHGs show room temperature mobilities of 0.5-4 cm(2) V-1 s(-1) and do not freeze out at low temperatures. A characteristic alloy fluctuation energy of 1.0 eV for hole scattering in InGaN alloy is proposed based on the experiments.