The origins of the DX center formation in unintentionally doped GaN epilayers grown on sapphire substrates

Photoconductivity (PC) and photoluminescence (PL) measurements on unintenti onally doped GaN epilayers grown on sapphire substrates by using plasma-ass isted molecular beam epitaxy were performed to investigate the origins of t he DX center in the GaN layers. Temperature-dependent PL measurements showe d a shallow-deep transition behavior. The capture barrier height of the don or by the electron was 64 meV, and the transition energy between the donor and the deep center and the potential barrier height between the shallow le vel and the deep level were -0.51 and 0.574 eV, respectively. These results indicate that the DX center in unintentionally doped GaN epilayers origina te from the oxygen impurity. (C) 2001 Elsevier Science B.V. All rights rese rved.