Photoluminescence from a - and m -plane GaN:Be,O

Photoluminescence (PL) from Be-implanted GaN containing a high concentration of oxygen was investigated. The GaN crystals were grown along nonpolar crystallographic directions by hydride vapor phase epitaxy on ammonothermal substrates. After ultrahigh-pressure annealing, secondary ion mass spectrometry revealed box-shaped Be diffusion profiles, while the concentration of unintentionally incorporated oxygen exceeded that of Be. The dominant defect-related emission at low temperatures is the yellow luminescence band (YLBe), which is unambiguously attributed to isolated BeGa acceptors. The PL exhibits all characteristic features previously reported for Be-doped GaN, including two-step thermal quenching of the YLBe band, its abrupt redshift at T ≈ 100 K, and the emergence of the ultraviolet luminescence (UVLBe3) band at T > 150 K, associated with the shallow state of the BeGa acceptor. A pronounced orientation-dependent effect is observed at 100–120 K: the YLBe intensity increases in nonpolar GaN samples but decreases in polar (c-plane) GaN:Be. This behavior is explained by differences in light-extraction efficiency from polaronic dipoles with different orientations, providing strong experimental confirmation of the previously proposed BeGa acceptor model.