Transport characteristics of 2DHG in p-GaN/AlGaN/GaN heterojunctions: the 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 Mg impurities within the p-GaN layer is investigated through rapid thermal processing treatments at temperatures ranging from 700 to 900 °C in N₂ and N₂ + O₂ environments. The samples annealed in an N₂ atmosphere exhibited a higher sheet resistance (R_s) of 50 × 10³ Ω □⁻¹ and a lower carrier concentration (p) of 1.13 × 10¹⁸ cm⁻³ compared to those annealed in an N₂ + O₂ atmosphere, which had values of R_s = 40 × 10³ Ω □⁻¹ and p = 1.41 × 10¹⁸ cm⁻³ at room temperature (RT). The sheet resistance and Hall measurement as a function of temperature were determined for a selected set of samples annealed in N₂ + O₂ at 780, 860, and 900 °C to assess effective dopant activation and determine the R_s and p values in the p-GaN layer. A pristine sample was used as a reference to monitor possible variation in the R_s and p values upon dopant activation procedures. Analysis of the R_s and p data at T < 100 K allowed distinguishing between holes generated from acceptor ionization in the p-GaN layer with an average activation energy of 129 ± 4 meV and holes in the 2DHG at the p-GaN/AlGaN interface with a hole density of ∼6 × 10¹² cm⁻². The formation and electrical properties of the 2DHG were determined to be completely independent of the activation of Mg impurities in the p-GaN layer.