COMMENTS ON THE ORIGIN OF LOW-ENERGY STRUCTURE OBSERVED IN THE FAR-INFRARED CYCLOTRON-RESONANCE OF ULTRA-HIGH MOBILITY N-GAAS AND N-INP

Recently optically detected cyclotron resonance spectra reported by Ahmed et al in ultra-pure n-GaAs have revealed low-energy structure associated with the cyclotron resonance. We have investigated the far-infrared photoconductive response under conditions of cyclotron resonance in these n-GaAs (mu almost-equal-to 400 000 cm2 V-1 s-1) samples and also in n-InP (mu almost-equal-to 170 000 cm2 V-1 s-1) samples grown by MBE. The suggestion that the structure arises from transitions involving non-parabolicity and polaron coupling effects is discounted using a five-level P-p calculation as found in the literature. Other possible origins, supported by appropriate theory, are suggested for this structure.