Thermal stability of semi-insulating InP epilayers: The roles of dicarbon and carbon-hydrogen centers

Infrared- (IR) absorption measurements of localized vibrational modes (LVM's) show the presence of H-C(p) pairs and isolated C(p) acceptors in semi-insulating epitaxial layers of InP. Rapid transient anneals of two sets of such samples at temperatures of up to 800 deg C lead to the complete loss of the H-C(p) pairs and large decreases of [C(p)], from initial values of 5.8 x 10(exp 18) and 2.5 x 10(exp 18) cm(exp -3). The layers remain semi-insulating up to 700 deg C and, even after annealing at 800 deg C, they show only low n-type conductivities (n about 10(exp 16) cm(exp -3)) implying the continued presence of a sufficient concentration of donor centers to effect near compensation. Raman scattering measurements reveal LVM's (IR inactive), close to 1800 cm(exp -1) and broadbands, due to amorphous carbon, that show increased strengths after annealing. The LVM's are attributed to deep donor dicarbon split-interstitial centers occupying phosphorus lattice sites, analogous to corresponding centers observed in annealed highly carbon-doped p-type GaAs and AlAs that have been investigated by local-density-functional calculations. No evidence is found for the presence of shallow donors, namely V(In)H4 complexes, C(In) donors or P(In) antisite defects. Changes in the unusual electric-field broadening of the C(p) LVM, revealed by IR measurements, are related to the reductions in die concentration of C(p) defects resulting from the anneals. These calculations give further insight about the compensating defects and may imply reductions in strain after the higher-temperature anneals.