P15. A polarization-induced 2D hole gas in undoped gallium nitride quantum wells

Science (2019) [Direct download link]

R. Chaudhuri, S. Bader, Z. Chen, D. Muller, H. Xing, D. Jena

Featured in Cornell Chronicle, Semiconductor Today, EurekaAlert!, ScienceDaily, Phys.org

(Editor's Feature) A Hole Flatland :

When two distinct materials are placed on top of each other, the difference in polarization between the two layers can induce charge carriers at the interface. Many such two-dimensional (2D) electron gases have been observed, but engineering a 2D hole gas without the help of doping has been much trickier. Chaudhuri et al. used molecular beam epitaxy to grow a layer of gallium nitride on top of aluminum nitride without introducing dopants. This approach resulted in a high-density 2D hole gas at the interface in this technologically relevant system.

P14. High conductivity Polarization-induced 2D hole gases in Undoped GaN/AlN Heterojunctions enabled by Impurity Blocking Layers

Journal of Applied Physics (2021)

Reet Chaudhuri, Zhen Chen, David A. Muller, Huili Grace Xing, Debdeep Jena

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 ∆ps > 7e13 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 ∆ps ≤ 1 e13 cm−2 across growths, and a 3× boost in the Hall mobilities. These changes result in a 2-3× increase in hole conductivity when compared to GaN/AlN structures without IBLs.

P12. Electric Fields and Surface Fermi Level in Undoped GaN/AlN Two-Dimensional Hole Gas Heterostructures

physica status solidi rrl (2021)

Łukasz Janicki*, Reet Chaudhuri*, Samuel James Bader, Huili Grace Xing, Debdeep Jena, Robert Kudrawiec

*co-first author

III-nitride heterostructures have a high built-in electric field due to the intrinsic polarization. Contactless electro-reflectance (CER) spectroscopy is used to porbe and measure the built-in electric field in GaN/AlN 2DHG heterostructures. Comparing to electrostatic simulations, a surface barrier height of ≈1.9 eV for holes is proposed in these technologically relevant heterostructures.