Encapsulation and annealing studies of semi- insulating InP

Photoluminescence spectroscopy, secondary ion mass spectrometry and Hall profiling measurements are used to study the effects of encapsulation and annealing on semi-insulating (SI) InP. Control of both indium and phosphorus loss from the InP surface during annealing is necessary to prevent anomalous activation of shallow, low dose silicon implants in SI InP. Phosphorus vacancy-related complexes are detected for encapsulant deposition temperatures in excess of 300°C and their concentration increases with increased deposition temperatures. Indium out-diffusion is detected for furnace anneals at 750°C for 30 min of samples capped with oxygen-free silicon nitride (Si₃N₄) or phosphosilicate glass (PSG), but substantially more indium is detected in the PSG film than in the Si₃N₄. Silicon indiffusion is greatest for PSG-capped InP grown by the liquid-encapsulated Czochralski method and least for Si₃N₄-capped material grown by liquid phase epitaxy. Conducting layers with sheet electron concentrations approaching 2×10¹² cm^-2 are always formed in PSG-capped samples, but only occasionally in Si₃N₄-capped samples. Net doping is strongly correlated with indium out-diffusion and silicon in-diffusion, suggesting that under the anneal conditions studied here the supply of indium vacancies limits silicon in-diffusion from the cap and also plays a significant role in determining the amount of doping produced from the in-diffused silicon. Iron was observed to be gettered to the encapsulant-substrate interfacee and, in some Si₃N₄-capped samples, to be depleted from the near-surface region. These results point to the need for low temperature dielectric deposition processes and rapid thermal annealing for controllable low dose implant activation in SI InP.