Growth of p-type ZnTe and n-type CdSe films on GaAs(001) by pulsed laser ablation

Thin films of p-type ZnTe and n-type CdSe were deposited on (001) and 2°-miscut GaAs wafers by ArF (193 nm) pulsed laser ablation of stoichiometric ZnTe and CdSe targets through several ambient gas compositions and total pressures. Films were grown both with the substrate facing the plume (φ = 0°) and with the substrate rotated by an angle, φ > 0°. Substrates were affixed to the heater using conventional indium bonding and an indium-free method. Hall effect measurements were performed to determine the influence of target-to-substrate separation (D _TS ), substrate temperature, gas composition and total pressure, substrate orientation (φ), bonding method, and substrate miscut on the carrier concentration and mobility. NH ₃ was found to be largely ineffective for p-type doping of ZnTe under the conditions explored and especially when compared to the wide range of resistivities achievable by employing nitrogen. In one instance, however, a free-hole concentration of 2 × 10 ¹⁸ cm ^-3 (μ ≈ 3 cm ² /V · s) was achieved by depositing at a large distance (D _TS = 17.5 cm) and low temperature (200°C) in 20 mTorr of NH ₃ . The Hall effect data for CdSe were found to cluster into two distinct regimes, one with mobilities ≤ 0.3 cm ² /V · s and carrier concentrations ≥ 3 × 10 ²⁰ cm ^-3 , the other with mobilities ≥ 30 cm ² /V · s and carrier concentrations ≤4 × 10 ¹⁸ cm ^-3 . Examination of X-ray diffraction data coupled with reflection high-energy electron diffraction (RHEED) measurements, observations of the films' surfaces, and secondary ion mass spectroscopy (SIMS) profiling, indicated that no single-growth parameter was responsible for the observed bimodal behavior.