Hetero- and multi-quantum well structures in wide-gap II-VI semiconductors
Résumé
A quite large programme on wide-gap II-VI materials has been developed in our group. The aim of this paper is to present this work. The choice of material, ZnSe based, is obviously due to the value of this gap (2.7 eV) at room temperature. This material is the most promising for blue-light-emitting diodes, or devices for non-linear optics applications. This paper will be divided into four parts. In the first one the problem of ZnSe/GaAs obtained by OMCVD will be treated. In particular, the band energy diagram at the interface, and in some cases the appearance of a hole gas in the GaAs side, gives rise to some misinterpretation, concerning the p-type conduction of ZnSe.
Also the state of the strain of the ZnSe layer depending on the used substrate, is deduced by the shift of the photoluminescence peak.
In the second part we extend our discussion to superlattice ZnSe-ZnTe. By using a simple envelope function model, with a given band offset, the critical thickness of barriers and wells are calculated to obtain an emission in the blue wavelength.
In the third part the offset is calculated by a self-consistent tight-binding method for the series of Zn chalcogenides. Then, the electronic structure of ZnTe-CdTe superlattices is calculated. Interface states appear due to strong coupling between light and heavy holes when the tight-binding model is used.