Transport characteristics of 2DHG in p-GaN/AlGaN/GaN heterojunction: impact of Mg dopant activation

Abstract

This work investigates the correlation between the two-dimensional hole gas (2DHG) formed at the p-GaN/AlGaN interface and the activation of dopants in the p-GaN layer grown on top of the AlGaN/GaN heterojunction. The effect of annealing environment and temperature on the activation of the Mg impurities within a p-GaN layer is investigated by rapid thermal processing treatments at temperatures ranging from 700 to 900 °C in N₂ and N₂+O₂ environments. Samples annealed in an N₂ atmosphere showed higher sheet resistance (R s ) and lower carrier concentration (p) compared to those annealed in an N₂+O₂ atmosphere at room temperature (RT). Sheet resistance and Hall measurement as a function of temperature were performed on a selected set of samples annealed in N₂+O₂ at 780, 860, and 900 °C to assess effective dopant activation and determine R s and p values in the p-GaN layer. A pristine sample was used as a reference to monitor possible variation of the R s and p values upon dopant activation procedure. Analysis of the R s and p data at T < 100 K allowed to distinguish between holes generated from acceptor ionization in the p-GaN layer and holes in the 2DHG at the p-GaN/AlGaN interface. The formation and electrical properties of 2DHG were determined to be completely independent of the activation of Mg impurities in the p-GaN layer.