Thermal stability of semi-insulating InP epilayers: The roles of dicarbon and carbon-hydrogen centers - art. no. 205307

Infrared- (IR) absorption measurements of localized vibrational modes (LVM' s) show the presence of H-C-P pairs and isolated C-P accepters in semi-insu lating epitaxial layers of LnP. Rapid transient anneals of two sets of such samples at temperatures of up to 800 degreesC 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(18) and 2.5 x 10(18) cm(-3). The layers remain semi-insulating up to 70 0 degreesC and, even after annealing at 800 degreesC, they show only low n- type conductivities (n similar to 10(16) cm(-3)), implying the continued pr esence of a sufficient concentration of donor centers to effect near compen sation. Raman scattering measurements reveal LVM's (IR inactive), close to 1800 cm(-1) and broadbands, due to amorphous carbon, that show increased st rengths after annealing. The LVM's are attributed to deep donor dicarbon sp lit-interstitial centers occupying phosphorus lattice sites, analogous to c orresponding centers observed in annealed highly carbon-doped p-type GaAs a nd AlAs that have been investigated by local-density-functional calculation s. No evidence is found for the presence of shallow donors, namely VInH4 co mplexes, C-In donors or P-In antisite defects. Changes in the unusual elect ric-field broadening of the C-P LVM, revealed by IR measurements, are relat ed to the reductions in the concentration of C-P defects resulting from the anneals. These calculations give further insight about the compensating de fects and may imply reductions in strain after the higher-temperature annea ls.