Impact of Sulphide Passivation of the Substrate on the Photoluminescent Properties of InAs Autoepitaxial Layers

The photoluminescent properties of autoepitaxial layers of indium arsenide are studied using low-temperature Fourier-transform infrared spectroscopy. The structures are grown by the method of chlorine hydride vapour-phase epitaxy on heavily doped n+-InAs substrates. Sulfide passivation of the substrates is carried out in a unimolar aqueous solution of sodium sulfide at room temperature, which leads to the removal of the natural oxide layer and the formation of a sulfur layer protecting the substrate surface. Three separate peaks are detected in the photoluminescence spectra of the structures, measured with a Fourier-transform infrared spectrometer at a temperature of 8 K. The peak with an energy of 415 meV is attributed to a direct interband transition in indium arsenide. The power dependence of the second peak, with an energy of 400 meV, is sublinear, which makes it possible to attribute it to the emission of bound excitons. In the PL line of the third peak with a maximum at an energy of 388 meV, a fine structure with a series of closely spaced peaks is observed, which allows us to attribute this signal to the emission of donor-acceptor pairs. The influence of substrate sulfidization on the quality of InAs epitaxial layers is assessed by comparing the relative area of the PL peak of bound excitons for sulfidized and nonsulfidized structures. It is shown that the decrease in the relative peak area of bound excitons after sulfidization of the substrate is due to a decrease in the number of defects in the autoepitaxial InAs layers.