Photoelectronic Properties of Graded Composition Crystals of II-VI Semiconductors

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Abstract
Various photoelectronic properties of (Zn, Cd)S, (Zn, Cd)Te, and Zn(Se, Te) graded composition crystals are reported. From the position dependences of the optical absorption and of the electrical conductivity, the graded energy‐band diagrams of the three systems are determined. Position‐dependent photoluminescence is observed in the (Zn, Cd)S and Zn(Se, Te) graded heterojunctions, and shifts in the luminescent spectra with applied electric field are interpreted in terms of field‐enchanced minority‐carrier transport between regions of different bandgap. The photoconductivity is observed to depend on bias for the (Zn, Cd)Te graded heterojunctions and explained on the basis of the energy‐band diagrams. The magnitude, sign, and spectral response of the photovoltage are measured and interpreted in terms of the band‐edge gradients. The temperature dependence of the photovoltage is determined and related to the temperature dependence of the dark conductivity. From the data and their analysis, general features of II‐VI compound graded heterojunctions are deduced.