SWIFT HEAVY-ION-INDUCED DEFECT STUDY IN EPITAXIAL N-TYPE GAAS FROM IN-SITU HALL-EFFECT MEASUREMENTS

N-type (Si-doped, N-D approximate to 10(17) cm(-3)) GaAs epitaxial lay ers (MOCVD) are irradiated at 77 K with oxygen (0.163 GeV), krypton (5 .15 GeV), xenon (5.73 GeV) and at 300 K with krypton (5.15 GeV). Hall effect measurements are performed, in situ, with increasing fluence. A decrease of the electron concentration and a degradation of the Hall mobility, respectively due to trapping and to scattering on irradiatio n-induced point defects are pointed out. In the heavily doped layers, shallow donor impurities merge with the conduction band in distorted b and tail. A simple two band conduction model is used as a simulation t ool, which allows the carrier Hall concentration variation to be corre ctly fitted, as a function of both temperature and ion fluence. The Ha ll mobility versus fluence variation at 77 K, which is mainly limited by screened ionized impurities and defects, is also simulated. From th ese simulations, the arsenic vacancy levels E-1 and E-2 are most likel y to correspond respectively to single acceptor (-/0) and single donor (0/+) transitions. The introduction rates of induced defects (in part icular V-As) are estimated: the total experimental introduction rate a ppears to be about 50% of the theoretical atomic displacement rate ass ociated with nuclear collisions, independently of ion nature and of te mperature. Although electronic stopping power S-e is about 2000 times larger than nuclear stopping power S-n, it is then suggested that irra diation-induced electronic excitation, in the investigated range S-e = 1-12 MeV/mu m, has no effect on the degradation of n-type GaAs epitax ial layers.