OPTICAL-DETECTION OF CYCLOTRON-RESONANCE FOR CHARACTERIZATION OF RECOMBINATION PROCESSES IN SEMICONDUCTORS

Novel applications of the technique of optically detected cyclotron resonance (ODCR) are discussed. This method is an extension of the conventional cyclotron resonance investigations and shows important advantages when applied to characterization of semiconductor materials. These advantages are due to a higher sensitivity and a longer momentum relaxation time caused by photoneutralization of ionized impurities. This in turn enables experiments at lower magnetic fields and lower microwave radiation frequency. Photoexcitation used in ODCR often results in a simultaneous observation of electron and hole cyclotron resonances in the same sample, which is a rare case in a conventional CR study. High magnetic field far infrared ODCR experiments utilize all these advantages of the method. For the most common X-band (10 GHz) microwave setups, the ODCR resolution often is too low to allow accurate CR determination of the band structure parameters of the material studied. In that case, ODCR may be used for high-resolution photoluminescence experiments and for identification of carrier capture and recombination paths at impurities, as was proposed recently. These new and important applications of the ODCR technique are described here, and documented by recent experimental results. The mechanism of ODCR detection for pure and doped semiconductors is discussed, and a prominent role of the impact ionization mechanism is demonstrated. This is followed by a discussion of recent applications of ODCR for identification of recombination mechanisms. Then high spectral resolution ODCR experiments are described, with the example of overlapping free-to-bound and donor-acceptor pair transitions. Some special applications of ODCR are demonstrated. ODCR also can be applied to analyze quantum confinement of carriers in two-dimensional (2D) structures such as heterojunctions and quantum wells. It is shown that useful information can be obtained on the electronic properties of the 2D electron (or hole) gas and the interlayer carrier transfer enhanced by carrier heating at CR absorption in such structures.