ELECTRON AND NEUTRON RADIATION-INDUCED ORDER EFFECT IN GALLIUM-ARSENIDE

We investigate electron (7 MeV) and neutron (1 MeV equivalent fluence damage in silicon) radiation effects in gallium arsenide grown by the metallorganic chemical vapor deposition method. One series of samples was intentionally undoped, and another was doped n-type to 2.5x10(15) Si/cm(3) The sample irradiations were done at room temperature. The fluences ranged from 10(10) to 6x10(15) cm(-2) for electron irradiation and from 10(12) to 3x10(15) cm(-2) for fisson spectrum neutron irradiation expressed as 1 MeV equivalent fluence in silicon. The radiation damage was characterized by low temperature photoluminescence (PL) measurements using 1.58 eV laser excitation, deep level transient spectroscopy (DLTS), and transport measurements. The PL intensity increases with fluence at first and reaches its maximum at about 10(13) n/cm(2) or at about 10(12) e/cm(2) before decreasing at higher fluence. Oscillations in the PL intensity for the acceptor levels mere observed as a function of electron fluence. DLTS reveals that the density of electron trap EL12 is reduced at a rate of 10(4)cm(-1) at 10(10) e/cm(2) but it is reintroduced at higher fluences. Electron irradiation reduces a hole trap concentration at low fluences. Neutron irradiation reduces EL12 concentration at a rate of 0.5 cm(-1) at 3x10(13) n/cm(2), and reintroduces it at higher fluences. Both electron and neutron irradiation introduce EL6 at 3x10(12) e/cm(2) and 10(13) n/cm(2) at a rate Of 0.30 +/- 0.04 cm(-1). Only neutron irradiation introduces the U band starting from 3x10(12) n/cm(2). Trap EL14 is introduced at a rate of 1.7+/-0.4 cm(-1) starting from 10(14) n/cm(2). Electron irradiation introduces EL14 above 10(14) e/cm(2). There is some correlation between the introduction of these traps and the nonmonotonic behavior of the PL intensity. The decrease of trap concentration accompanied with an increase in PL intensity at lower fluences, an increase in the density of traps at higher fluences, and a fluence dependent oscillatory PL intensity for acceptor levels indicate radiation-induced Order at low fluences followed with a non-uniform reorganization of defects with radiation in GaAs.