Laser Induced Defects in GaAs Layers

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Abstract
Annealing of ion implanted GaAs layers as well as irradiation of unimplanted samples with nanosecond laser pulses is connected with the formation of exponential absorption tails near the fundamental absorption edge with the dependenceK˜ exp [ħω(E)−1] on the photon energy. Identical behaviour is found in weakly damaged ion implanted layers. The observed high near edge absorption is connected with almost no refractive index change. The characteristic energyEis independent on the implanted ion species and increases with the nuclear deposited energy density and the laser energy density from about ≈ 0.1 eV up to a maximum value of 0.52 eV. The defects responsible for this behaviour act as compensating centers for free carriers. The experimental findings and the missing pronounced absorption tail in irradiated silicon supports the conclusion that defects typical for compound semiconductors are produced. Assuming high concentrations of vacancies and anti‐site defects the experimentally found values forEcan be explained from theoretical calculations.