Preparation of InP-based semiconductor materials with low density of defects: effect of Nd, Ho and Tb addition

Specific features of some rare earth elements (REE=Nd, Ho or Tb) are exploited to improve structural, optical and electrical properties of InP-based layer compounds for applications in ionising radiation detector structures. InP layers were grown by liquid phase epitaxy on (100)-oriented single crystal InP substrates with individual REE addition to the melt. The dependence of the layer thickness, overall surface morphology and defect density on the growth conditions were monitored by employing optical and scanning electron microscopy. The evaluation of electrical properties was gained from C–V measurements performed with the mercury probe and from a free carrier concentration profile determined by the probe profiling method on bevelled samples. The low-temperature photoluminescence spectroscopy was used to study the changes in optical properties. Significant improvement of all the studied layer parameters with increasing amount of REE in the melt was observed up to certain critical value of REE concentration. The density of structural defects was reduced by more than a half order of magnitude, free carrier concentration was reduced effectively by up to four orders of magnitude, photoluminescence peaks were narrowed substantially and fine spectral features were resolved. The conductivity of layers prepared with Tb admixture changed from n to p type when Tb exceeded certain limit of concentration in the melt.