Optical-pumping study of spin-dependent recombination in GaAs

Abstract

Optical-pumping techniques provide a convenient way to study-dependent recombination (SDR) processes at deep impurity centers in semiconductors. Indeed, by changing the polarization of excitation light, it is possible to modify the photoelectron spin polarization in a controlled way. This produces a change in luminescence intensity if the recombination is spin dependent and if the centers are spin polarized. The basic physical ideas which govern this type of study are discussed. Two different experimental situations are presented which show the possible effect of the external magnetic field parallel to the excitation direction. In semi-insulating GaAs, we find from an analysis of the effect on the luminescence band attributed to the EL2 center that this center is dynamically polarized by the photoelectrons, and that the spin-dependent character of the recombination at this center modifies both the free-electron concentration and polarization. These effects strongly increase with magnetic field and are approximately a factor of 3 larger than those calculated from a simple model. Possible reasons for this are discussed. The second situation we consider is the recombination on manganese acceptors in GaAs. These centers are thermodynamically polarized by the magnetic field and the corresponding SDR is conveniently monitored from the intensity of manganese emission since the photoelectron concentration is not modified by SDR. This shows the paramagnetic character of the manganese level in GaAs. The nature of this level is discussed. We emphasize that the present method can be used as a preliminary step to find the appropriate magnetic field and luminescence wavelength for optical detection of magnetic resonance.