Crystallization of II-VI semiconductor compounds forming long microcrystalline linear assemblies

Abstract

In this work we report the formation of long microcrystalline linear self-assemblies observed during the thin film growth of several II-VI compounds. Polycrystalline CdTe, CdS, CdCO 3 , and nanocrystalline CdTe:Al thin films were prepared on glass substrates by different deposition techniques. In order to observe these crystalline formations in the polycrystalline materials, the thin film growth was suspended before the grains reached to form a continuous layer. The chains of semiconductor crystals were observed among many isolated and randomly distributed grains. Since CdTe, CdTe:Al, CdS and CdCO 3 are not ferroelectric and/or ferromagnetic materials, the relevant problem would be to explain what is the mechanism through which the grains are held together to form linear chains. It is well known that some nanocrystalline materials form rods and wires by means of electrostatic forces. This occurs in polar semiconductors, where it is assumed that the attraction forces between surface polar faces of the small crystals are the responsible for the chains formation. Since there are not too many mechanisms responsible for the attraction we assume that a dipolar interaction is the force that originates the formation of chain-like grain clusters. The study of this property can be useful for the understanding of nucleation processes in the growth of semiconductor thin films.

Emerging II-VI wide bandgap semiconductor device technologies

“…Mostly, II-VI group materials have a direct band gap with high optical absorption coefficients, therefore absorption of around 99% of the impinged photon having energy higher than the band gap energy observed for a small layer thickness of ~1.0 μm [2,3]. Nowadays, these versatile semiconductor materials are applied extensively to electronic, optical, and photovoltaic devices including light-emitting diodes [4][5][6] thin-film transistors [7] optical waveguides [8] photodetectors [9] solar cells [10,11] and catalyst applications [12]. The cadmium and zinc-based groups of II-VI semiconductors (CdS, CdTe, CdSe, ZnS, ZnSe, ZnTe) have two main phases (i) zincblende and (ii) wurtzite in the bulk form [13].…”