Adsorption, desorption, and interdiffusion in atomic layer epitaxy of CdTe and CdZnTe

TL;DR

This study investigates the growth mechanisms of CdTe and CdZnTe films via atomic layer epitaxy, revealing how growth parameters influence self-regulation, composition, and the role of adsorption and desorption processes.

Contribution

It provides new insights into the growth regimes of CdTe and CdZnTe films, highlighting the impact of purge times and exposure durations on self-regulation and composition control.

Findings

ZnTe growth follows an ALE regime with one monolayer per cycle.

CdTe growth varies with exposure and purge times, affecting self-regulation.

Surface Cd atoms are substituted by Zn, influencing alloy composition.

Abstract

The mechanisms controlling the growth rate and composition of epitaxial CdTe and CdZnTe films were studied. The films were grown by isothermal closed space configuration technique. A GaAs 100 substrate was exposed sequentially to the elemental sources, Zn, Te, and Cd, in isothermal conditions. While growth of ZnTe followed an atomic layer epitaxy, ALE, regime self regulated at one monolayer per cycle; the CdTe films revealed different growth rates in dependence of the growth parameters,exposure and purge times. Combination of short purge times and larger Cd exposure times led to not self regulated growth regime for CdTe. This is ascribed to large Cd coverages that were dependent on Cd exposure times, following a Brunauer-Emmett and Teller-type adsorption. However, for longer purge times and or short Cd exposure times, an ALE self regulated regime was achieved with 2 ML per cycle. In this sense, the self-regulation of the growth is limited by desorption, instead of absorption, as in the traditional growth technique. Cd atoms substitution by Zn atoms and subsequent evaporation of surface Cd atoms during Zn exposure has been proved. The influence of these facts on the growth and composition of the alloy is discussed.