The decay of carbon, luminescence in liquid-encapsulated Czochralski-grown semi-insulating GaAs

Abstract

In undoped liquid-encapsulated Czochralski-grown semi-insulating gallium arsenide (LEC SI GaAs), the carbon acceptor, C_AS, is responsible for the ∼1.49 eV emission due to donor-acceptor (D–A) pair radiative recombination. We have studied the effect of different carbon concentrations on the line shape and decay kinetics at and near the D–A emission peak for temperatures ranging from 4.2 to 34 K. The photoluminescence decay has been found to follow a double exponential law at the early stage of the decay but follows a power law of the form L(t)αT^−p at a later stage. Analysis of the temperature dependence of the exponential components gives two activation energies of ≃5.7 and ≃15 meV. We find that the 5.7 meV is most likely associated with Si_Ga shallow donor, while the 15 meV is due to a more indirect process involving an EL2 related donor cluster near 20 meV. The exponent, p, of the power-law decay is found to be both temperature (T) and concentration dependent of the form p = βT −1, where β is a linear function of the concentration of the acceptors, C_As, in the temperature range of 18 ⩽ T < 30 K. A promising, simplified model based on a continuous set of trapping levels is presented and compared to the experiments. Some aspects of the observed exponential and power law decays are predicted by the theory.