Passivation of InP with thin layers of MBE-grown CdS

Thin layers of CdS were grown on (100) n-InP by molecular beam epitaxy (MBE). Substrates were pre-treated in an ammonia/thiourea solution, then annealed at ~150-250°C in vacuo prior to CdS growth. A single effusion cell with a polycrystalline CdS source was used. Reflection high energy electron diffraction (RHEED) analysis showed surface reconstruction following predeposition anneals at 200°C of sulfur-passivated InP. Subsequent CdS deposition at 200°C resulted in lattice-matched epitaxial layers in the metastable cubic phase, as observed with RHEED. X-ray photo-electron spectroscopy (XPS) analysis of the CdS/InP structures showed that the near-surface of InP is phosphorus deficient following the pre-deposition anneal, with an In₂S ₃ layer present at the substrate/CdS interface. Subsequent processing of MIS structures with CdS layers (25-85 Å) between the InP and SiO₂ resulted in MIS capacitors with consistently low density of interface states (2×10¹¹ eV^-1 cm ^-2) and hysteresis (20 mV)