Measurement of GaN/Ge(001) Heterojunction Valence Band Offset by X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) at the GaN/Ge heterostructure interface. The VBO is directly determined to be 1.13±0.19 eV, according to the relationship between the conduction band offset ΔE_C and the valence band offset ΔE_V: Δ E_C=E_g^GaN-E_g^Ge-Δ E_V, and taking the room-temperature band-gaps as 3.4 and 0.67 eV for GaN and Ge, respectively. The conduction band offset is deduced to be 1.6\pm 0.19 eV, which indicates a type-I band alignment for GaN/Ge. Accurate determination of the valence and conduction band offsets is important for the use of GaN/Ge based devices.