TEMPERATURE-DEPENDENCE OF THE EL2 METASTABILITY IN SEMIINSULATING GAAS - THERMAL HYSTERESIS BETWEEN THE METASTABLE AND REVERSE TRANSITIONS

The temperature dependence of the photoquenching of the EL2 level in s emi-insulating GaAs is studied by photocurrent and thermally stimulate d currents. The observations made in these experimental procedures tog ether with other results reported in the literature reveal that the me tastable transformation of EL2 cannot be fully achieved when the sampl e temperature is above 85 K. This observation is compared with the the rmal recovery of the EL2 ground state from its metastable configuratio n EL2, which is known to take place between 120 and 130 K; showing th us the existence of a conspicuous thermal hysteresis between both tran sitions, EL2-->EL2 and EL2*-->EL2. This is analyzed in terms of the e xistence of a level that would play the role of an actuator of the met astable transformation of EL2. The charge state of this level can be a ltered by both optical excitation and temperature. Above 85 K it would be thermally emptied, being in such a charge state configuration unab le to activate the metastable transformation of EL2.