Far Infrared Studies in Epitaxial Films of III-V and IV-VI Semiconductors. Submillimeter Far-Infrared Spectroscopy in the Liquid and Solid States with a Tunable Optically Pumped Laser.

摘要

The conventional two-oscillator model together with the assumption of an abrupt interface has been used to fit far-infrared reflection and transmission data for the epitaxial-substrate systems PbSe on NaCl, Pb(0.79)Sn(0.21)Te on Pb(0.79)Sn(0.21)Te, and InAs on semi-insulating GaAs. The model worked well for the first system but failed for the other two. These results suggest, as Tennant and Cape found for PbSnTe, that interface effects appear in far-infrared data. The interface phenomena appear to involve free-carrier mixing across the interface in the PbSnTe system and both carrier and lattice mixing in InAs-GaAs. The joint measurement of reflection and transmission was found especially helpful in analyzing interface behavior. A new high-power pumped far-infrared laser spectrometer was used to make the transmission measurements. The design and spectroscopic application of a submillimeter-far-infrared (FIR) optically pumped tunable laser are described. Driven by 15-25 W of power from a cw CO2 laser, the FIR system gave milliwatts of power between 96 and 1217 micrometers. The pumped media were methyl alcohol and 1,1-difluoroethylene. The laser spectrometer was used to measure the transmission of liquid H2O, the bulk semiconductor GaAs, the epitaxial semiconductor InAs, and the high-temperature superconductor V3Si. In general, the laser system gave vastly improved signal-to-noise ratios, reduced stray light problems, and increased penetration power relative to more conventional FIR spectrometers.