HIGH-FIELD SPIN-RESONANCE OF WEAKLY-BOUND ELECTRONS IN GAAS

Electron spin resonance (ESR) of shallow donor electrons in n-type GaA s has been observed by means of direct detection of microwave absorpti on at magnetic fields of 6-11 T. The ESR structure is smeared out over a magnetic field range of up to 1 T. The line shape is strongly asymm etric and depends on the magnetic-field sweep direction. These unusual features are assigned to microwave-induced nuclear polarization under ESR conditions, leading to strong effective nuclear fields (Overhause r shift). The ESR curves show a signature of nuclear magnetic resonanc e if an additional radio-frequency field is applied. The observed ESR line shape is well reproduced by numerical simulation. Furthermore, th e Lande g factor of weakly localized electrons in GaAs has been accura tely determined (g = -0.464+/-0.002 at B = 0).