Formation of EL2, AsGa and U band in irradiated GaAs: Effects of annealing

Abstract

Gallium arsenide (GaAs) which was grown by metallorganic chemical vapor deposition, doped n with silicon to 2×1015 cm−3, and irradiated at room temperature with 1 MeV neutrons in the fluence range 1012 cm−2 to 3×1015 cm−2, has been studied by deep level transient spectroscopy (DLTS) and by far infrared photoluminescence (PL) spectroscopy. We report the effect of annealing at 550 °C for 30 min, which, in irradiated GaAs, is to introduce the gallium vacancy (VGa). The DLTS signal at 780±40 meV, attributed to the EL2 deep level, has an introduction rate of about 3×10−2 cm−1 in the unannealed case, and 0.19±0.02 cm−1 in the annealed case. The PL signal at 702 meV has been attributed to a phonon-assisted transition of the EL2 defect, a defect which has been identified as the isolated arsenic antisite (AsGa+). The PL peak increases in intensity up to fluences of 3×1013 cm−2, before decreasing at higher fluences. After annealing, its intensity increases up to fluences of 1015 cm−2, before decreasing at the highest fluence studied. The similar behavior of the DLTS and PL signals with respect to irradiation and annealing confirms that they have the same origin. It also supports the AsGa point defect model of EL2. The decrease in PL intensity at high fluences is attributed to radiationless transitions involving radiation-induced complexes such as the U band, EL6, and EL14 observed by DLTS. After annealing, the concentration of these defects is reduced to a large extent, but weaker sharper peaks remain in the DLTS spectrum. We suggest that the U band consists of complexes involving AsGa and acceptors like VGa.