Thermal recovery of photoquenchedEL2 infrared absorption in GaAs

The thermal recovery of the GaAs EL2 infrared absorption from the metastable (EL2*) back to the normal (EL2⁰) state after it has been completely photoquenched (EL2⁰{→}EL2*) has been studied for the temperature range 70 K{≤}T{≤}150 K and compared to previous photocapacitance recovery measurements. Complete recovery profiles (absorption coefficient versus time) were measured at 2-K intervals for 106 K{≤}T{≤}150 K and partial profiles were measured for T<106 K. For 100 K{≤}T{≤}120 K, the absorption recovery was in good agreement with published photocapacitance recovery data. One sample exhibited an activation energy of 0.30±{}0.01 eV, but a second sample showed an energy of 0.25±{}0.01 eV. These energies are believed to represent the thermal barrier between EL2* and the conduction band. The different values probably reflect the fact that EL2 is a ``family'' of defects with different configurations exhibiting different thermal recovery barriers. For T>120 K, the absorption recovers much more slowly than the photocapacitance, with an apparent activation energy of about 0.07 eV.