Electrical and optical properties of semi-insulating InP obtained by wafer and ingot annealing

Thick blocks and wafers of Fe-doped InP (semiconducting and semi-insulating) were annealed at 900 °C and characterized by Hall effect and absorption measurements. In the absorption spectrum of annealed InP, the line at 2315.6 cm−1 (probably originated by the complex VIn(PH)4) is strongly decreased or even suppressed. The decrease of this line is probably connected with annihilation of the complexes via out-diffusion of hydrogen. The absorption measurements also showed that a small amount of shallow acceptors (around 1014 cm−3) is reactivated by the annealing. The free carrier concentration is found to be remarkably lower after thermal annealing. These results support the hypothesis that in liquid encapsulated Czochralski (LEC)-grown InP some shallow levels (donors and acceptors) are related to complexes involving hydrogen. The annealing-related conversion to the semi-insulating state of semiconducting InP is achieved when the sum of Fe and shallow acceptors is greater than the residual donor concentration.