EL2 Related Anomalous Splitting in the Photoreflectance Response of Semi-Insulating GaAs

Anomalous splitting has been observed in the photoreflectance (PR) response of SI:GaAs in the vicinity of the exciton at 78 K. Recent photohiminescence (PL) measurements suggest the splitting is correlated with the EL2 content of the samples. Separation between the two peaks in PR measurements range from about 2 to 4 meV. A striking effect is that each peak is maximized by a different phase setting of the lock-in. The splitting is sample dependent and is also affected by several other factors including surface conditions, temperature, pump beam intensity and modulation frequency.