Controlled vapor-pressure heat-treatment effect on deep levels in liquid-encapsulated czochralski-grown GaP crystals

Photocapacitance (PHCAP) measurements have been carried out on GaP crystals grown by the liquid-encapsulated Czochralski (LEC) method with heat treatment under various phosphorus-vapor pressures at different temperatures. Electron traps of Ec-1.1 eV, Ec-1.6 eV, Ec-1.9 eV, and a hole trap of Ev+2.26 eV are mainly detected. The phosphorus-vapor pressure dependence of the Ec-1.9 eV trap density and their diffusion behavior indicate that they are interstitial phosphorus atoms. The densities of both Ec-1.1 eV and Ec-1.6 eV traps are strongly dependent on the shallow impurity concentrations. Moreover, the density of Ec-1.1 eV traps increases with increasing phosphorus-vapor pressure. From these results, we suggest that Ec-1.1 eV traps are the complexes of shallow donors and antisite phosphorus atoms. Deep-level densities in GaP crystals after annealing at 860°C or 960°C for 60 min are decreased almost one order of magnitude lower than those in untreated substrate crystals, which should have occurred via out-diffusion of interstitial phosphorus atoms. However, such an effect is not prominent for 800°C treatment for 60 min.