Quantum photoyield of diamond(111)—A stable negative-affinity emitter

Quantum photoyield and secondary-electron distributions are presented for an unreconstructed diamond (111) surface (type-IIb, gem-quality blue-white semiconductor). This chemically inert surface exhibits a negative electron affinity, resulting in a stable quantum yield that increases linearly from photothreshold (5. 5 eV) to 20% at 9 eV, with a very large yield of 40%-70% for 1335 eV. For all photon energies, secondary-electron energy distributions show a dominant 0. 5-eV-wide emission peak at the conduction-band minimum (₁^min=5. 500. 05 eV above the valence-band maximum {₂₅}^'). In contrast with recent self-consistent calculations J. Ihm, S. G. Louie, and M. L. Cohen, Phys. Rev. B 17, 769 (1978) no occupied intrinsic surface states with ionization energies in the fundamental gap (the Fermi level was 1 eV above {₂₅}^') were observed. Likewise, the measured photothreshold (Eₕ₀₂-{₂₅}^') is significantly smaller than calculated (7. 00. 7 eV).