Variation of Chemical and Photoluminescence Properties of Mg-Doped GaN Caused by High-Temperature Process

Abstract

We characterize the chemical and photoluminescence (PL) properties of GaN with Mg doping densities of 7×1017 and 2×1019 cm-3, particularly focusing on their variations caused by the high-temperature process. Before the thermal process, band-edge emission dominated the PL spectrum in the lightly Mg-doped GaN, whereas luminescence at 3.2 eV with a high intensity similar to that of the band-edge line was observed in the highly Mg-doped GaN. For the lightly Mg-doped GaN, the thermal process at 900 °C enhanced the intensity of the broad band in the energy range from 1.5 to 2.5 eV. Pronounced Ga outdiffusion caused by the high-temperature process was also confirmed by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy, indicating that these emission lines originate from the transitions between the conduction band and deep levels related to a defect complex involving a Ga vacancy (VGa + X). For the highly Mg-doped GaN, the peak energy of the dominant PL line abruptly changed from 3.2 to 2.8 eV after the process at 1000 °C. Simultaneously, a non uniform profile of Mg density was found near the GaN surface, arising from the pronounced surface segregation of Mg. It is thus likely that a defect complex involving a Mg interstitial and a Ga vacancy (MgI + VGa) is responsible for the 2.8 eV band in the highly Mg-doped and high-temperature-processed GaN.