Bias-controlled hole degeneracy and implications for quantifying spin polarization

We report on a spin injection study from an Fe Schottky tunnel contact into n-AlGaAsGaAsp- AlGaAs light-emitting diodes with a bulk-like GaAs recombination region. The spectral composition and circular polarization of the electroluminescence allowed us to monitor changes in the band structure induced by the applied bias voltage. At low bias conditions, the holes are confined at the GaAsp-AlGaAs interface and have two-dimensional (2D) character with nondegenerate heavy- and light-hole subbands. Increasing the bias voltage moves the structure towards a flatband condition, making the holes three-dimensional (3D)-like. The results are discussed in terms of the quantum selection rules describing radiative recombination in 2D and 3D systems.