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Type-II band alignment of low-boron-content BGaN/GaN heterostructures

The band offset parameters of low-boron-content BGaN/GaN heterojunctions have been studied using x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) in BxGa1−xN epilayers (x  ⩽  0.043) grown on GaN/sapphire and AlN/sapphire templates. A staggered-gap (type-II) band alignment has been identified at the BGaN/GaN heterojunction by XPS. A study of the red shift of deep-level-related yellow PL band and the band gap shrinkage of BGaN epilayers with increasing boron content confirmed the type-II band alignment and enabled us to estimate that the ratio of the conduction-to-valence band discontinuity is 57:43. It is also shown that the band gap bowing of the BGaN alloy system is accommodated in the conduction band.