THz cyclotron resonance of 2D hole gases in GaN/AlN heterostructures in pulsed magnetic fields

The recent discovery of highly conducting two-dimensional hole gases (2DHG) in GaN/AlN hetero-junctions has opened the door to efficient complementary GaN electronics[1], a long-standing challenge in wide-bandgap semiconductor device physics. Simulations and electrical transport studies indicate that both heavy- and light-hole valence bands are occupied in these 2DHGs, but direct experimental characterization of the fundamental parameters of the mobile holes remains at an early stage. Historically, cyclotron resonance is a powerful tool to study the mobile carriers in semiconductors, but it is challenging to employ in p-type GaN-based structures because the hole effective masses are large, and scattering times are short, necessitating very large magnetic fields and THz frequencies. Here, we use time-domain terahertz spectroscopy and pulsed magnetic fields >30 T to directly measure the complex optical conductivity and cyclotron resonance of both heavy and light holes in these GaN-based 2DHGs, revealing their effective masses, densities, scattering times, and mobilities.

[1] Chaudhuri, Reet, et al. "A polarization-induced 2D hole gas in undoped gallium nitride quantum wells." Science 365.6460 (2019): 1454-1457.