Crystallization processes of thin polycrystalline layers of galium stybnide for thermophotovoltaic application

Abstract

The cost of thermophotovoltaic converters can be reduced by making substrates of amorphous materials, which do not have an orienting effect, such as glass or fused quartz, for obtaining thin polycrystalline GaSb layers. The study establishes the conditions for the crystallization of thin polycrystalline GaSb layers with grain size sufficient to produce efficient thermophotovoltaic converter structures on a non-orienting substrate made of fused quartz. The authors carry out a two-dimensional modeling of the initial nucleus growth to study how the crystallization conditions affect the shape of the grains. It is shown that the form of grain growth is not very sensitive to the initial nucleus size and cooling rate, but is rather sensitive to nucleus density on the surface. The paper provides an estimate of the average surface density of the new phase nuclei, which tend to grow, on substrate surfaces. When the temperature is increased, the surface concentration of nuclei grows, and the grain size decreases. It is determined that the selected range of grain surface density corresponds to the cultivation temperature range of 450—550°С. Thin polycrystalline GaSb layers are grown at 520°С with a cooling rate of 10°C/ min to a temperature of 400°C, using a method developed by us, which requires simple equipment and consists in the forced cooling of a thin layer of stibium in a gallium melt in a vacuum. The degree of crystallinity of the samples is estimated from the photoluminescence spectra at 77 K. The spectra show two emission bands: one at 796 meV and another, the predominant one, at 775 meV, which indicates the presence of a significant number of point defects and deviations from the stoichiometry of the obtained films. The studies performed on an interference microscope show that the obtained layers have good planarity and homogeneity, and the average grain size is up to 25 microns, which confirms the validity of the proposed models. This technology can be used to manufacture inexpensive infrared radiation converters and, in particular, thermophotovoltaic converters.