The stability of electrical parameters of CdTe layers produced by metal - organic chemical vapour deposition

Abstract

The stability of structures consisting of p-type high-resistivity epitaxial layers of CdTe grown by metal - organic chemical vapour deposition technology was studied by monitoring the capacitance and the AC and DC conductances of structures. The structures were grown on substrates differing in their conductivity type and composition. The structure parameters were measured in the frequency range 0.5 - 1000 kHz immediately after fabrication, after storage for half a year in the dark at room temperature and after ultrasonic processing. It was found that the stability of the epilayer parameters against ageing and acoustic treatments depended strongly on the substrate characteristics. The ageing and the epilayer degradation due to the ultrasonic processing were found to be a result of the diffusion of mobile acceptor defects from the substrate to the epilayer. The highest electric parameter stability was found for the epi-CdTe/n-CdTe structure. It is shown that the main reason for this stability is the potential barrier at the p - n junction, which prevents the acceptor defects from diffusing out of the substrate.

Layered structure formation in Hg1−xCdxTe films after high-frequency sonication

“…On the other hand, the change of epilayer properties is possible in the issue of zinc diffusion from the substrate. As has been shown in [13], acoustic wave treatment stimulates the out-diffusion of mobile defects from the CdTe substrate in p-type CdTe MOCVD epilayers.…”

The effect of high-frequency sonication on charge carrier transport in LPE and MBE HgCdTe layers

“…In other words, the wave propagation process and energy dissipation have taken place mainly in the substrate. According to [8], where the authors have investigated the stability of the CdTe epilayer parameters against ageing and acoustic treatments, acoustic vibrations of the sub-threshold power level stimulate the dissociation of defect complexes in the substrate material, resulting in an increase in the concentration of mobile defects and their diffusion from the substrate to the epilayer. Hence, it could be expected that the sonically stimulated processes at the substrate do have considerable influence on the stability of epilayer parameters.…”

“…It is also known that in the A 2 B 6 semiconductor compounds zinc has an intrinsic tendency to form not only substitutional defects but also interstitials. Interstitial zinc, which is a mobile donor defect, usually creates clusters and precipitates at various kinds of macrodefects in the crystal (dislocations, grain boundaries and twins) [8]. One can assume that sonically stimulated cluster dissociation occurs and escape of zinc from sinks results in the formation of a CdZnTe compound with bigger composition in comparison with the matrix.…”