Abstract
Cu doping of ZnTe, which is an important semiconductor for various optoelectronic applications, has been successfully achieved previously by several techniques. However, besides its electrical transport characteristics, other physical and chemical properties of heavily Cu-doped ZnTe have not been reported. We found an interesting self-assembled formation of crystalline well-aligned Cu-Te nano-rods near the surface of heavily Cu-doped ZnTe thin films grown via the molecular beam epitaxy technique. A phenomenological growth model is presented based on the observed crystallographic morphology and measured chemical composition of the nano-rods using various imaging and chemical analysis techniques. When substitutional doping reaches its limit, the extra Cu atoms favor an up-migration toward the surface, leading to a one-dimensional surface modulation and formation of Cu-Te nano-rods, which explain unusual observations on the reflection high energy electron diffraction patterns and apparent resistivity of these thin films. This study provides an insight into some unexpected chemical reactions involved in the heavily Cu-doped ZnTe thin films, which may be applied to other material systems that contain a dopant having strong reactivity with the host matrix.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1741-x) contains supplementary material, which is available to authorized users.
Highlights
ZnTe bulk crystal has increasing importance for various advanced semiconductor applications such as solar cells, blue-green laser diodes, terahertz imaging, electro-optic detector, and holographic interferometry [1,2,3,4,5,6,7]
We discovered the formation of one-dimensional (1D) surface modulation and Cu-Te nano-rods for heavily Cu-doped ZnTe thin films grown by MBE
The similar patterns observed for the ZnTe:Cu thin films grown using TCu ≥ 870 °C is likely due to a similar interaction between Cu atoms and ZnTe surface lattice when the incorporated Cu atoms reach a certain concentration
Summary
ZnTe bulk crystal has increasing importance for various advanced semiconductor applications such as solar cells, blue-green laser diodes, terahertz imaging, electro-optic detector, and holographic interferometry [1,2,3,4,5,6,7]. Among many options for p-type doping of ZnTe, nitrogen (N) doping [12,13,14,15,16] and copper (Cu) doping [17, 18] have been mostly studied. Liang et al Nanoscale Research Letters (2016) 11:531 resistivity of these thin films upon the increase of Cu cell temperature. Our work demonstrates that a highly reactive dopant could lead to formation of nanostructures in the host matrix, which may generally be applied to the studies of heavy doping using other physical or/and chemical vapor deposition approaches
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