Band offsets at metalorganic chemical vapor deposited β-(AlxGa1-x)2O3/β-Ga2O3 interfaces-Crystalline orientation dependence

The beta-(AlxGa1-x)(2)O-3 alloy represents an emerging ultrawide bandgap semiconductor material for applications in high-power electronics and deep ultraviolet optoelectronics. The recent demonstrations of orientation-dependent epitaxial growth of high quality beta-(AlxGa1-x)(2)O-3 films have unlocked prospects for the development of ultrahigh frequency beta-(AlxGa1-x)(2)O-3/Ga2O3 based transistors with high-power tolerance. To control the electronic and optical properties of beta-(AlxGa1-x)(2)O-3/Ga2O3 heterostructure-based devices, an understanding of the band offsets between beta-(AlxGa1-x)(2)O-3 and beta-Ga2O3 is crucial. However, there have been no systematic experimental studies on the evolution of the band offsets between differently oriented beta-(AlxGa1-x)(2)O-3/Ga2O3 heterointerfaces as a function of Al compositions. This work presents the valence and conduction band offsets at (010) and ( 2 over bar 01 ) oriented beta-(AlxGa1-x)(2)O-3/Ga2O3 interfaces using x-ray photoelectron spectroscopy. beta-(AlxGa1-x)(2)O-3 films with x <= 0.35 and x <= 0.48 were grown by metalorganic chemical vapor deposition on (010) and ( 2 over bar 01 ) oriented beta-Ga2O3 substrates, respectively. The determined band offsets reveal the formation of a type-II (staggered) band alignment at (010) oriented beta-(AlxGa1-x)(2)O-3/Ga2O3 and a type-I (straddling) heterojunction between ( 2 over bar 01 ) beta-(AlxGa1-x)(2)O-3 and beta-Ga2O3. For both crystalline orientations, the valence and conduction band offsets are found to increase with increasing Al content with a much weaker variation in the valence band offsets as compared to the conduction band offsets. Among different orientations investigated, such as (010), ( 2 over bar 01 ), and (100), the largest conduction band offset occurs at a beta-(AlxGa1-x)(2)O-3/Ga2O3 interface with (100) orientation, providing opportunities for excellent electron confinement with a high-density two-dimensional electron gas. Results from this study on the tunable and orientation-dependent band offsets with the variation of the Al alloy fraction will provide guidance for the design of heterostructures in future beta-(AlxGa1-x)(2)O-3/Ga2O3 based devices.

Automated summary

Understanding the band offsets between β-(AlxGa1-x)(2)O-3 and β-Ga2O3 is crucial for the development of high-power tolerant ultra-high frequency transistors. This study revealed the tunable and orientation-dependent band offsets at different oriented β-(AlxGa1-x)(2)O-3/Ga2O3 interfaces, providing valuable guidance for the design of future heterostructures in devices based on β-(AlxGa1-x)(2)O-3/Ga2O3.