Band Offsets of the MOCVD-Grown β-(Al0.21Ga0.79)2O3/β-Ga2O3 (010) Heterojunction

The band offsets for the β-(Al0.21Ga0.79)2O3/β-Ga2O3 (010) heterojunction have been experimentally measured by X-ray photoelectron spectroscopy. High-quality β-(Al0.21Ga0.79)2O3 films were grown by metal-organic chemical vapor deposition for characterization. The indirect band gap of β-(Al0.21Ga0.79)2O3 was determined by optical transmission to be 4.69 ± 0.03 eV with a direct transition of 5.37 ± 0.03 eV, while β-Ga2O3 was confirmed to have an indirect band gap of 4.52 ± 0.03 eV with a direct transition of 4.94 ± 0.03 eV. The resulting band alignment at the heterojunction was determined to be of type II with the valence and conduction band edges of β-(Al0.21Ga0.79)2O3 being -0.26 ± 0.08 and 0.43 ± 0.08 eV, respectively, above those of β-Ga2O3 (010). These values can now be used to help better design and predict the performance of β-(AlxGa1-x)2O3 heterojunction-based devices.

Temperature Dependence of Breakdown Field in p-π-n GaN Diodes

We present the results of the study of the electric breakdown in p-π-n GaN diodes. The breakdown is observed at reverse biases above 40 V and is accompanied by the formation of microplasmas. The study shows that the observed breakdown field in GaN (on the order of 1 to 2 MV/cm) increases with the temperature. This feature makes GaN very promising for high power devices and avalanche photodetectors, operating at elevated temperatures.

Growth of a-plane ZnO Thin Films on r-plane Sapphire by Plasma-assisted MBE

ZnO thin films have been epitaxially grown on r-plane sapphire by RF-plasma-assisted molecular beam epitaxy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicate that the epitaxial relationship between ZnO and r-plane sapphire is (1120)ZnO // (1102)sapphire and [0001]ZnO // [1101]sapphire. Atomic force microscopy measurements reveal islands extended along the sapphire [1101] direction. XRD omega rocking curves for the ZnO (1120) reflection measured either parallel or perpendicular to the island direction suggest the defect density anisotropy along these directions. Due to the small lattice mismatch along the ZnO [0001] direction, few misfit dislocations were observed at the ZnO/Al2O3 interface in the high-resolution cross-sectional TEM image with the zone axis along the ZnO [1100] direction.