FORMATION OF EL2, AS(GA) AND U-BAND IN IRRADIATED GAAS - EFFECTS OF ANNEALING

Gallium arsenide (GaAs) which was grown by metallorganic chemical vapo r deposition, doped n with silicon to 2X10(15) cm(-3), and irradiated at roam temperature with 1 MeV neutrons in the fluence range 10(12) cm (-2) to 3X10(15) cm(-2), has been studied by deep level transient spec troscopy (DLTS) and by far infrared photoluminescence (PL) spectroscop y. We report the effect of annealing at 550 degrees C for 30 min, whic h, in irradiated GaAs, is to introduce the gallium vacancy (V-Ga). The DLTS signal at 780+/-40 meV, attributed to the EL2 deep level, has an introduction rate of about 3x10(-2) cm(-1) in the unannealed case, an d 0.19+/-0.02 cm(-1) in the annealed case. The PL signal at 702 meV ha s been attributed to a phonon-assisted transition of the EL2 defect, a defect which has been identified as the isolated arsenic antisite (As -Ga(+)). The PL peak increases in intensity up to fluences of 3X10(13) cm(-2) before decreasing at higher fluences, After annealing, its int ensity increases up to fluences of 10(15) 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 h ave the same origin. It also supports the As-Ga point defect model of EL2. The decrease in PL intensity at high fluences is attributed to ra diationless transitions involving radiation-induced complexes such as the U band, EL6, and EL14 observed by DLTS. After annealing, the conce ntration of these defects is reduced to a large extent, bat weaker sha rper peaks remain in the DLTS spectrum. We suggest that the U band con sists of complexes involving As-Ga and accepters like V-Ga. (C) 1996 A merican Institute Physics.