Optical conductivity in alloys: Optical effective mass

A generalized Kubo formula for the optical conductivity and the associated optical mass in alloys is derived for off-diagonal randomness and analyzed in the dilute limit. A possible resolution for the decrease in the optical mass upon alloying observed in certain dilute alloys is suggested.     

Zn1-xCdx S合金薄膜的结构和光学性质

采用低压金属有机化学气相沉积(LP-MOCVD)技术,在普通石英衬底上制备出不同Cd组分(0．02,0．44,0．59,0．83,0．91)的Zn1-xCdxS合金薄膜材料。X射线测量表明样品为单一取向的纤锌矿结构,并且随着x的增加衍射峰位基本成线性地从ZnS衍射峰向CdS衍射峰移动。此外,在PL谱中还可以看出随着样品中Cd含量的增加,发光峰从3．66eV红移到2．43eV。根据发光峰位与Zn1-xCdxS中x的变化关系,推导出它们之间的关系近似为Eg(Zn1-xCdxS)=3．61-1．56x 0．38x^2。还探讨了不同Cd组分薄膜材料的X射线衍射峰半峰全宽以及发光峰半峰全宽的变化。     

Optical absorption in cubic Zn1-xMnxSe under hydrostatic pressure

The optical absorption edges of the diluted magnetic semiconductors Zn_1-xMn_xSe have been measured under hydrostatic pressure for x ≦ 0.25. We found a blue shift of the direct interband gap with pressure which is nearly independent of the manganese concentration. An absorption band at 2.62 eV is assigned to the intra-atomic transition ⁶A₁ → ⁴A₁, ⁴E of the manganese ions. Its pressure shift indicates an increase of the d-p-hybridization which is, however, weaker than in the tellurides. Additional bands appear at sufficiently high pressures in samples with x = 0.15 and 0.25.     

The semiconductor-electrolyte interface : Optical transitions in CdMnTe alloys

The junction p-Cd_1?xMn_xTe-electrolyte is studied under monochromatic illumination for the alloy composition range 0 ≤ x ≤ 0.7. Optical transitions in the semiconductor are evidenced by photocurrent measurements. In the composition range 0 ≤ x ≤ 0.45, the nature of the fundamental transition appears to be the same as in CdTe (valence band Γ → conduction band Γ ). For x > 0.45, the observed photocurrent p

ak, pinned at a consta

t energy value ca. 2.1 eV, may presumably be related to a transition Γ → d(Mn) level whereas the photocurrent edge associated to the forme

transition increases linearly with x.     

Phase transitions in RbCaF3. I: Optical studies

Phase transitions in RbCaF₃ have been investigated by optical birefringence measurements and Raman scattering experiments. A near discontinuity in the onset of spontaneous birefringence at 196 K shows that the cubic to tetragonal phase change is “slightly” first order. The Raman spectra of the tetragonal phase support a D¹⁸_4h structure in which two phonons of A_1g and E_g symmetry soften as the 196 K transition is approached from lower temperatures. A very slow transition to a lower symmetry structure was observed at about 42 K in the Raman measurements.     

Optical spectra and electronic transitions in gallium phosphide crystals

Analysis of the long-wave edge of the self-absorption spectrum of gallium phosphide crystals not distorted by line structure at low temperatures enabled us to determine the characteristic parameters of indirect transitions. In GaP crystals of a different type the appearance of a discrete structure in the long-wave absorption edge is related to the localization of excitons near impurities of an unknown nature. This is confirmed by the appearance in these crystals of an intense green electroluminescence band at low temperatures.The authors are grateful to I. Ryzhikov, A. Kruchinin, and Yu. Il'in for providing the crystals used in the experiments.