X-ray diffraction measurement for selenium and sulfur under high pressure was performed through the angle dispersive method. The structural-transition sequence similar to that of Te was found and the unified interpretation was obtained for pressure-induced structural phase transition of VIb element except for oxygen. In the case of solid C70, the transition from fcc to a simple rhombohedral structure was observed and the rhombohedral phase was concluded to be realized by the partial freezing out of molecular rotation.
The effects of the hydrostatic pressure on the optical gap Eg of the amorphous Ge-chalcogenide semiconductors are reviewed. The absorption edge Eg shifts largely to low frequency side and the parameter Γ of the Urbach tail increases with the increase of the pressure. For the composition near GeS2, sudden anomalous changes of Eg and also Γ are observed in the pressure range of 2∼4 GPa. These anomalous effects are considered to originate from the change of the internal structure. Raman spectra exhibit interesting large change under the pressure especially in the low frequency region, and the characteristic properties of the Raman spectra of the amorphous Ge-chalcogenide semiconductors are also reviewed.
The relationship is outlined between the mixed-valence state and the electronic structure in the halogen-bridged platinum compounds. Pressure dependences of the optical absorption edge and the Raman frequency of halide stretching mode are interpreted in terms of the electron-lattice coupling characteristic of the PtX chains. Presented are the results of the recent optical experiments on the pressure-induced phase transition in PtCl and PtBr, demonstrating the role of the long range order among the chains. Also discussed is the behavior of the midgap absorption band, which is attributable to solitons, in PtCl under high pressures.
The photoluminescences (PL) in semimagnetic semiconductor CdMnTe are reviewed except quantum wells. There are three kinds of PL related to energy gap, excited states of d-electrons with the character of localized states and unknown infrared PL. The formation of magnetic polaron, giant g-factor of electrons and holes of band, stable point of excited Mn ion are discussed from photoluminescence. The excited states of infrared PL is assigned as d-electron excited states with large lattice distortion using pressure coefficient of photoluminescence peak energy and time profile of the PL intensity.
we review the electronic structure of GaAs/AlAs short-period superlattices, which have been clarified through optical measurements under high pressure. The symmetry of the conduction subband in the superlattices is discussed on the basis of the pressure dependence of the photoluminesce. Based on the energy and lifetime vs. pressure data, pressure-induced Γ-X band mixing effect is also discussed In addition, we describe the band discontinuity in GaAs/AlInP quantum well structures, which has been determined by high-pressure photoluminescence measurements.
High-pressure photoluminescence (PL) studies of ordered Ga0. 5In0. 5P alloys grown on GaAs substrates by metalorganic vapor phase epitaxy (MOVPE) are reviewed. The anomalous reduction in the direct band-gap energy and the high-pressure PL behavior depend on growth temperature and substrate misorientation. The possible explanations for some of the trends and the complexities involved in PL properties in ordered GaInP samples are presented, which include effects of repulsion between theΓ-folded energy states in the CuPt-type ordered structure.
Current-voltage characteristics of triple barriers resonant tunneling diodes has been measured at a temperature of 77 K and pressures up to 2 GPa. Peak-to-valley current ratio (PVR) of the diode decreased as increasing pressure. This change is explained qualitatively in terms of a variation of the effective mass of electron under pressure.
Density of expanded fluid selenium was measured in the temperature and pressure ranges up to 1650°C and 700 bar including the liquid-vapor critical point by the x-ray absorption method . For the measurements, a new type of cell made of polycrystalline sapphire and a high-pressure vessel of authors' own design were developed We obtained the critical temperature, pressure and density of 1615±5°C, 385±5 bar and 1. 85±0. 03 gcm3, respectively. The anomaly that isochores bend in the semiconductor-metal transition region was observed, and we found that the isochores again bend in the metal-insulator transition region near the critical point. The diameter in the liquid-vapor coexistence curve is deviated strongly from the law of the rectilinear diameter to the liquid side near the critical point.