High conductivity Polarization-induced 2D hole gases in Undoped GaN/AlN Heterojunctions enabled by Impurity Blocking Layers

TL;DR

This paper demonstrates that introducing impurity blocking layers in undoped GaN/AlN heterostructures significantly stabilizes 2D hole gas densities and enhances mobility, advancing the development of high-performance wide-bandgap semiconductor devices.

Contribution

The study introduces impurity blocking layers in GaN/AlN heterostructures, reducing variability and boosting hole mobility and conductivity of 2D hole gases.

Findings

Reduced hole density variation to ≤ 1 x 10^{13} cm^{-2}

Tripled Hall mobility in heterostructures with IBLs

Increased hole conductivity by 2-3 times

Abstract

High-conductivity undoped GaN/AlN 2D hole gases (2DHGs), the p-type dual of the AlGaN/GaN 2D electron gases (2DEGs), have offered valuable insights into hole transport in GaN and enabled the first GaN GHz RF p-channel FETs. They are an important step towards high-speed and high-power complementary electronics with wide-bandgap semiconductors. These technologically and scientifically relevant 2D hole gases are perceived to be not as robust as the 2DEGs because structurally similar heterostructures exhibit wide variations of the hole density over $\Delta p_s >$ 7 x 10$^{13}$ cm$^{-2}$, and low mobilities. In this work, we uncover that the variations are tied to undesired dopant impurities such as Silicon and Oxygen floating up from the nucleation interface. By introducing impurity blocking layers (IBLs) in the AlN buffer layer, we eliminate the variability in 2D hole gas densities and transport properties, resulting in a much tighter-control over the 2DHG density variations to $\Delta p_s \leq$ 1 x 10$^{13}$ cm$^{-2}$ across growths, and a 3x boost in the Hall mobilities. These changes result in a 2-3x increase in hole conductivity when compared to GaN/AlN structures without IBLs.