AN OPTICALLY DETECTED CYCLOTRON-RESONANCE STUDY OF BULK GAAS

We have measured optically detected cyclotron resonance using far-infr ared radiation on an exceptionally pure sample of GaAs in fields up to 15.5 T. This relatively new experimental technique is shown to offer high resolution of free and donor impurity-bound electron transitions without the reproducibility problems of photoconductivity. The data co nfirm the existence of metastable donor states and provide a detailed picture of chemical shifts. The optically detected cyclotron resonance signal represents an interaction between the donor bound electron sta tes which are influenced by the far-infrared radiation and the donor b ound exciton states which are responsible for the photoluminescence. A ttenuation of the luminescence intensity under far-infrared illuminati on is primarily the result of a photothermal effect. At high fields, t here is indication of an interaction between the electron and excitoni c energy levels.