OPTICALLY DETECTED NUCLEAR-MAGNETIC-RESONANCE IN SEMICONDUCTOR QUANTUM-WELLS

We demonstrate use of a spatially selective optical pumping technique to investigate NMR in GaAs quantum wells. The method has previously been used to study bulk semiconductors but not lower dimensional systems. For this its sensitivity (<1011 spins) and optical selectively offer unique advantages which allow discrimination of quantum well nuclei from those in the substrate and buffer layers. Circularly polarised interband optical excitation and recombination are used to generate and monitor spin-polarised conduction electrons. The nuclear spins of the lattice are strongly polarised by contact hyperfine interaction (AI.S) with electrons, and NMR is detected as a dip in circular polarisation of the electron recombination radiation at resonance. The technique has a variety of possible applications including study of confined electron distributions, measurement of strain in stained layer systems via quadrupole splitting of NMR, and detection and identification of impurities. © 1990.