Characterisation of InP and GaInAsP layers prepared by liquid-phase epitaxy using holmium doping and gettering

A series of InP and GaInAsP (λg = 1.3 μm) layer samples were prepared by liquid-phase epitaxy from melts containing 0–0.5 wt.% of the rare-earth element holmium. The growth process was carried out in a horizontal multiple-bin graphite boat in a high-purity H2 atmosphere. The layers were grown on (100)-oriented InP substrates at 630 °C. The samples were examined by various physical diagnostic techniques; among them, photoluminescence spectroscopy was the most important. There are no indications of the holmium ions being incorporated into the host lattice sites to form optically active centres. The impact of a Ho admixture is nonetheless quite dramatic, especially on the carrier density, which is decreased by two-and-a-half orders of magnitude, and on the photoluminescence spectra which become markedly narrowed and their fine features are resolved. These effects are attributed to holmium acting as a very efficient gettering agent with regard to shallow donors. AIIIBV semiconductor layers with low background carrier concentrations are of interest for high quality detectors and devices destined for very high frequency operation.