Spin polarization in photo- and electroluminescence of InAs and metal/InAs hybrid structures

We report the magnetic field dependence of the degree of circular polarization on electroluminescence (EL) from InAs Schottky diode with ferro- and non-ferromagnetic electrodes by measuring the sigma(+) and sigma(-) components of the luminescence P-L intensity. These data are compared with reference photoluminescence (PL) data from p-InAs substrate. We found an interesting circular polarization behaviour of the positive slope (0 < B < 5 T) and the negative slope (5 T < B < 10 T) reaching a maximum value of 12-15% at B approximate to 5 T in both non-magnetic Schottky diode (EL data) and p-InAs substrate (PL data). The positive dependence is presumably attributed to the Zeeman effect and the negative dependence to magnetic depopulation of Landau levels of the valence band. We have also found an interesting behaviour of the degree of circular polarization from PL data as a function of external magnetic field containing double peaks. The intensity of the higher field peak is quenched at higher temperatures while the lower field peak stays almost the same. We attribute the higher field and lower field peaks to the radiative recombination of electrons with acceptor trapped holes and free excitons, respectively. The degree of circular polarization of the ferromagnetic metal Schottky diode was found to be negative and alters its sign according to the external magnetic field, B, and its magnitude reaches a maximum value of 12% at B approximate to +/-5 T. The clear difference between the ferro- and non-ferromagnetic samples indicates successful spin polarized electron injection from the ferromagnetic metal into the semiconductor. The net degree of circular polarization is estimated to be a much higher value of approximate to20% which is translated to be approximate to40% of spin injection efficiency assuming selection rules between heavy and light holes.