Interdefect correlation during thermal recovery ofEL2in semi-insulating GaAs: Proposal of a three-center-complex model

Photoquenching indications of a thermally triggered transition between two different EL2 metastable states in GaAs

“…The As Ga , initially in the position labeled as (1), is responsible for the metastability, whereas the Ga As controls the transition to the metastable state via the coulomb interaction with the neighboring As Ga [10]. Instead of a V As , as proposed by Fukuyama et al [10], our structure incorporates a V Ga , which is more easily justifi ed considering that it leads to an Asrich structure. In the following, we have labeled this state as EL2 0…”

“…As already proposed [10], the transition to the metastable state begins with a photoexcitation of the As Ga with a charge transfer from the Ga As , resulting in the breaking of the As GaGa As bond (Fig. 4b).…”

“…The triggering of this intermeditate transition with a small temperature increase, and the fact that it keeps proceeding despite a subsequent temperature reduction, seems to indicate a cooperative interaction mechanism between centers, similarly to what have been recently suggested in the case of the thermal recovery. [10]. It can also be infered from the measured time constant that the cross-section for the transition from the fundamental to the metastable state is about ten times larger than that for transition from the intermediate to the fi nal metastable state.…”

“…Later, evidences were accumulating that the center was more complex and required the presence of an actuator center, responsible for triggering the transition to the metastable confi guration of the center. [9] Recently, a three-center complex model has been proposed by Fukuyama et al [10] that seems to incorporate the necessary features, like the actuator level as well as the metastable state and photoquenching characteristics, but the matter is still open for investigation. In a recent work we presented indications of the existence of two metastable confi gurations, which seem to be accessed sequentially during the photoquenching process.…”

“…In this respect the mechanism behaves in similar way to the auto-catalytic thermal recovery process recently proposed by Fukuyama and colleagues, except for the fact that it happens in the opposite direction. [10] II. EXPERIMENT The sample investigated in this work consisted of a nominally undoped 1×1×2 cm 3 GaAs block containing 1.45× 10 16 cm −3 EL2 centers, as determined by optical absorption spectroscopy [12], and a carbon concentration of the order of 1×10 16 cm −3 , estimated from FFT-IR absorption.…”