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On the structured imperfections of bulk GaSb using High Resolution Transmission Electron Microscopy

Efstathios K. Polychroniadis 1,  Georgios I. Zoulis 1,  Spyros Konidaris 1,  Christos Lioutas 1,  Danuta Stroz 2

1. Dept. of Physics, Aristotle University of Thessaloniki, Thessaloniki 54 124, Greece
2. University of Silesia, Institute of Material Science, Bankowa 12, Katowice 40-007, Poland

Abstract

GaSb is a promising III-V direct band gap semiconductor with sphalerite type FCC structure. Its band gap value made it an excellent candidate for the conversion of infrared radiation to electricity. Furthermore, it can be used as a substrate material due to its lattice parameter matching ternary and quaternary III–V compounds. From the device point of view, GaSb based structures have shown potentiality for numerous applications such as booster cells for improved efficiency of photovoltaic cells and high efficiency thermophotovoltaic (TPV) cells. All the above clearly show the interest in any structural microscopic imperfections of the bulk GaSb, which affect its macroscopic usable properties.

The wafers of GaSb, that were studied, originated from ingots grown with the Liquid Encapsulated Chochralski method. In all cases, Energy Dispersive X-ray Spectroscopy and Particle Induced X-ray Emission measurements demonstrated an excess of Sb, suggesting the presence of Ga vacancy (VGa) and/or Sb antisite defects (SbGa). The aim of the present work is the study of the micro structural imperfections using High Resolution Electron Microscopy (HRTEM) to determine the specific point defects which lead to the detected Sb excess.

The samples heating was chosen to trigger the gathering of the point defects, so that they could be determined. Based on this, small clusters of ordered material from 10 up to 25nm, formed during heating experiments in the electron microscope, were studied by means of Electron Diffraction and HRTEM. The ordered structure axes were found to have a general relation with respect to the cubic ones as follows: ao=n2½ac, bo=2½ac/2 and co=[001]c. Moreover orientation variants in the two equivalent cubic [110] and [-110] directions were observed. From HRTEM image analysis a structural model is suggested. This is based mainly on the ordering of Sb antisite defects (SbGa) in two groups of sites and with different occupation values.
 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Efstathios K. Polychroniadis
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-10 17:30
Revised:   2009-06-07 00:44