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

Abstract

Infrared- (IR) absorption measurements of localized vibrational modes (LVM's) show the presence of ${\mathrm{H}\ensuremath{-}\mathrm{C}}_{\mathrm{P}}$ pairs and isolated ${\mathrm{C}}_{\mathrm{P}}$ acceptors in semi-insulating epitaxial layers of InP. Rapid transient anneals of two sets of such samples at temperatures of up to 800 \ifmmode^\circ\else\textdegree\fi{}C lead to the complete loss of the ${\mathrm{H}\ensuremath{-}\mathrm{C}}_{\mathrm{P}}$ pairs and large decreases of $[{\mathrm{C}}_{\mathrm{P}}],$ from initial values of $5.8\ifmmode\times\else\texttimes\fi{}{10}^{18}$ and $2.5\ifmmode\times\else\texttimes\fi{}{10}^{18}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ The layers remain semi-insulating up to 700 \ifmmode^\circ\else\textdegree\fi{}C and, even after annealing at 800 \ifmmode^\circ\else\textdegree\fi{}C, they show only low n-type conductivities $(n\ensuremath{\sim}{10}^{16}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}),$ 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 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ 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 ${V}_{\mathrm{In}}{\mathrm{H}}_{4}$ complexes, ${\mathrm{C}}_{\mathrm{In}}$ donors or ${\mathrm{P}}_{\mathrm{In}}$ antisite defects. Changes in the unusual electric-field broadening of the ${\mathrm{C}}_{\mathrm{P}}$ LVM, revealed by IR measurements, are related to the reductions in the concentration of ${\mathrm{C}}_{\mathrm{P}}$ 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.