Photoluminescence of GaP epitaxial layers obtained from indium-based melts

Abstract

In the present work, we investigate epitaxial layers of gallium phosphide grown on GaP substrates and doped by rare-earth elements (REE) Gd and Dy in the process of crystallisation from the melt-solutions on the base of In in the temperature interval of 975– 670 °C. REE concentration in the epitaxial layers was below the detection limit by X-ray spectral analysis (0.01 at. %). Photoluminescence spectra were measured in the temperature range of 4.2–300.0 K. In the spectra of the studied samples, typical for single-crystal GaP lines were observed: line of exciton bound on sulphur and phosphorus, as well as a series of narrow lines on the background of a broad band due to the donor – acceptor pair involving carbon and sulphur impurities. In the near-infrared range (1.4 –1.8 eV), a broad band due to the superposition of four bands with maxima near 1.53; 1.69; 1.85 and 1.35–1.40 eV was observed. The spectral shape and intensity of this band depended on the growth and doping conditions. The introduction Gd and Dy in melt resulted in occurrence of narrow X line (λ = 541 nm). Its intensity increased with the concentration increase of the REE in the melt. The photoluminescence intensity in all investigated region of waves lengths increased also with the addition of the REE in the melt-solution. This is most likely due to the increase in the lifetime of non-equilibrium charge carriers in GaP : REE. The mentioned X line was also observed in especially pure GaP layers. Then its intensity was considerably lower than in GaP : REE. The experimental data are explained by gettering in the melt of donor impurities (S, Se, Te) and formation of acceptor-type defects (presumably V P or Ga P ) in epitaxial layers of gallium phosphide when REE are introduced into the melt.