Investigation of the Interaction of Carbon Monoxide Laser Radiation with N-Indium

The Shubnikov-de Haas magneto-resistance oscillations and photoconductivity were experimentally studied in order to investigate the interaction of CO laser radiation with n-InSb at liquid helium temperatures. The roles of various absorption mechanisms on these effects were considered, particularly near the intrinsic band edge. From these measurements an effective electron temperature T(,e) was defined that increased or decreased under illumination, depending upon the strength of the applied electrical field. At Ohmic electric fields, the electron temperature was found to increase with increasing laser power and photon energy. Except for strong response at a photon energy of 236.6 meV observed in two of the samples, the results near the band edge were generally consistent with an impurity absorption model. A field induced negative photoconductivity (NPC) effect was observed for laser photon energies greater than about 233 meV with non-ohmic electric fields. In NPC the conductivity of a material decreases upon illumination. The NPC results were successfully interpreted on the basis of a laser induced cooling (LIC) model in which the decrease in conductivity is due to a decline in the electron temperature. Two mechanisms are described that can result in LIC: cold electron photo-injection (CEPI) and free carrier assisted transitions (FCAT). The LIC model is also supported by SdH effect measurements. This work represents the first detailed study of field induced NPC in InSb. An oscillatory instability on the trailing edge of the NPC signal was also observed. Many interesting effects have been reported in InSb near the intrinsic band edge. These phenomena rely upon the same absorption processes investigated here. Since InSb has practical device applications as well as being of theoretical interest, an extensive study of its absorption and transport properties gives an enhanced understanding of the interaction of infrared radiation with this material.