M. H. Maksimov

Energy gap and optical dielectric constant of Pb1−xCdxSe films

Abstract The transmission spectra of laser-deposited Pb 1− x Cd x Se films ( x = 0, 0.02, 0.05, 0.08 and 0.12) have been measured over the energy range 0.1–0.65 eV at two different temperatures 90 and 300 K. From these spectra the dispersion of the refractive index and the absorption coefficient-energy dependence have been obtained. Thus the dependences of the gap and the optical dielectric constant on the Cd content x have been investigated. The experimental results have been discussed in the framework of the recently developed theoretical model by Volkov and Pankratov et al 1,2 .

Thermoreflectance study of Pb1-xGexTe in the cubic and rhombohedral phases

Thermoreflectance spectra of Pb1-xGexTe (x=0, 0.02, 0.03, 0.07 and 0.1) have been investigated in the energy range 1.2 to 4.4 eV at temperatures above and below the phase transition temperature. The change of the interband transitions on the Ge content x in the cubic phase (300 K) have been obtained. Thermoreflectance spectra in the range of the transition temperature are broad, the structures are not clearly pronounced, which does not give the possibility of following the changes of the band structure in the range of the phase transition. The thermoreflectance spectrum of the rhombohedral Pb0.9Ge0.1Te at 40 K, well below the transition temperature of the compound, indicates the appearance of three additional structures of M0 type. These structures have been attributed to transitions at the critical points along the TW direction of the Brillouin zone.

Deep levels and persistent photoconductivity effects in undoped p-type PbTe films

Abstract High photosensitivity p-type PbTe layers have been grown by an electron-beam evaporation method. Time-resoved Hall effect and conductivity measurements showed a logarithmic photoconductivity behaviour for time periods between 101 and 105s. Extrapolation of the decay- to dark conductivity yields a total lifetime of the photoconductivity more than 107s at 77 K. The time constant decreases significantly at higher temperatures. The experimental results are interpreted in terms of a tunneling-assisted recombination of the persistent holes with spatially distributed trapped electrons.

Photoconductivity and electrical properties of epitaxial Pb1 − xCdxSe films

Abstract Photosensitive monocrystalline films Pb 1 − x Cd x Se ( x ⩽ 0.03) of low carrier concentration ( n = 0.3 ÷ 4 × 10 17 cm −3 have been grown by hot wall epitaxy method on cleaved (111)BaF 2 or (100)KCl substrates. Photoconductive thresholds determined by spectral response measurements (at temperatures 4.2, 77 and 300 K) were in good agreement with the fundamental absorption edges and showed a large increase in the energy gap E g with Cd content. Photoconductivity in the impurity range ( hv E g ) was observed. The temperature dependence of the Hall coefficient and the mobility between 4.2 and 300 K have been studied. Temperature freeze out of the free carriers was observed. Discussion of the carrier scattering mechanisms and impurity photoconductivity phenomena is presented.

Thermoreflectance study. II. Inter-band transitions in Pb1-xCdxSe alloys

For pt.I see ibid., vol.19, p.1771 (1986). Reflectance and thermoreflectance spectra of Pb1-xCdxSe (x=0.01 and 0.02) have been obtained at different temperatures in the energy range 1.4 to 4 eV. The spectral dependences of the optical constants have been obtained by Kramers-Kronig analysis of the reflectance data. The change of the inter-band transition energies on the cadmium content x have been obtained as a result of the quantitative interpretation of the thermoreflectance spectra. The analysis of the results has led to the conclusion that the cadmium atoms replace the Pb atoms in both octahedral and tetrahedral interstices of the selenium sublattice.

Thermoreflectance study. I. PbSe energy band structure

The spectral dependences of PbSe optical constants have been obtained by Kramers-Kronig analysis of the reflectance data in the energy range 1 to 4 eV. The thermoreflectance spectra of PbSe films, grown by two different techniques-hot wall epitaxy and laser-assisted deposition, have been investigated in the same energy range at temperatures 40, 80, 100, 200 and 300K. As a result of the quantitative interpretation of these spectra a detailed assignment of the energy levels has been obtained. The simultaneous investigation of the films grown by two different techniques has enabled their optical properties to be compared and some conclusions concerning the laser deposition technique to be drawn.