Improved control of composition and electrical properties of liquid phase epitaxial (CdHg)Te layers

Abstract The use of powdered HgTe as a source of mercury in a graphite sliding boat used for liquid phase epitaxial (LPE) growth of Cd x Hg 1− x Te alloys from Te-rich solutions at 460°C has been found to give excellent reproducibility of alloy composition, x and thickness due to the low Hg loss rates during growth (typically 0.3 mg min -1 ). Reproducibility of the wavelength corresponding to an absorption coefficient, α, of 500 cm -1 ( λ α = 500 ) is ± 0.15 μm, while the thickness reproducibility is typically ± 1 μm for 20μm thick layers. The variation of composition with depth in the layers is typically (2–4)x10 -4 in x per μm. Background carrier concentrations in undoped layers after Hg-rich annealing to remove Hg vacancies are n = (6–8) x 10 13 cm -3 . Using SIMS analysis we have shown that In is 100% electrically active after Hg-rich annealing and that the In dopant does not diffuse during the anneal treatment. Copper (Cu) doping has been studied for p-type material in the range 8×10 15 to 2×10 18 cm -3 . The Cu appears to be nearly 100% electrically active in as-grown layers, but during Hg-rich isothermal annealing at 250° C, a certain proportion of the Cu diffuses to the surface leaving only about 30% of the Cu in the bulk of the layer still electrically active.