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Direct observations of electronic states at metal-semiconductor junctions provide new information for understanding Schottky barrier formation. Low energy cathodoluminescence spectroscopy (CLS) offers a sensitive probe of near-surface and ‘buried’ interface states. These states are discrete and evolve with metal overlayer coverage to energies corresponding to Fermi level (EF) positions of the Schottky contact. CLS and photoluminescence spectroscopy (PL) also reveal that deep levels resident in the semiconductor bulk can dominate EF movements. By controlling atomic-scale interface chemistry, one can affect deep level production near the junction and thereby alter EF stabilization energies. Soft X-ray photoemission spectroscopy (SXPS) and internal photoemission measurements of barrier heights confirm this macroscopic effect. Examples include metals on clean, ordered GaAs, InP, CdTe, and InAlAs-InP heterojunctions. The SXPS-derived GaAs(100) barrier heights vs metal work function yield a self-consistent electrostatic analysis in terms of interface states actually observed by CLS. For GaAs (100) surfaces at low temperatures, such states are minimized and classic Schottky barrier formation is evident. These results highlight the extrinsic nature of metal-semiconductor interface states and the role of interface chemistry and bulk crystal quality in achieving near-ideal electronic properties. |
