D. Straub

Normal‐incidence grating spectrograph with large acceptance for inverse photoemission

A spectrometer for inverse photoemission in the vacuum ultraviolet range is described. A spherical grating with an acceptance of f/4 is used in normal incidence. Two position‐sensitive detectors allow the registration of spectra covering the whole range of photon energies from 8 to 28 eV in parallel. The optical resolution is 18 A for the Lyman‐α line of hydrogen. A space‐charge‐limited electron gun with an energy spread of 0.25 eV is used to excite inverse photoemission spectra. The large acceptance angle of the grating allows one to measure spectra with high efficiency and low background level.

Unoccupied surface state and conduction band critical points of GaP(110): A high resolution inverse photoemission study

We report the first angle‐resolved, high‐resolution inverse photoemission study of the cleaved (110) surface of GaP. The experiment was performed at normal electron incidence for electron energies between 11.6 and 18.6 eV. We are able to resolve the unoccupied dangling bond surface state in the band gap of GaP at 0.3 eV below the conduction band minimum. The maximum of the Γ1 X1 band is found at about 4.5 eV.We report the first angle‐resolved, high‐resolution inverse photoemission study of the cleaved (110) surface of GaP. The experiment was performed at normal electron incidence for electron energies between 11.6 and 18.6 eV. We are able to resolve the unoccupied dangling bond surface state in the band gap of GaP at 0.3 eV below the conduction band minimum. The maximum of the Γ1 X1 band is found at about 4.5 eV.

Inverse photoemission as a probe for unoccupied electronic states

Abstract Inverse photoemission is shown to be complementary to photoemission in probing unoccupied electronic states. The momentum of delocalized valence states can be measured as well as their energy if low electron (photon) energies in the 10–40 eV range are used: Thus, energy band dispersions are obtained for bulk, surface, and adsorbate states which cannot be determined by other techniques. Applications are demonstrated for Si, GaAs, SiO 2 and metal-semiconductor interfaces.

Inverse photoemission in the UV

Abstract Inverse photoemission (or bremsstrahlung spectroscopy) is the time-reversed photoemission process. Electronic states are probed via radiative transitions of an incoming electron into unoccupied states. X-ray bremsstrahlung spectroscopy is a well-established technique but its extension to the ultraviolet (with electrons incident at about 4–30 eV energy) has only begun recently. With lower electron energies the surface sensitivity increases such that monolayers can be probed. Also, the momentum of electrons in a solid can be determined by angle-resolved inverse photoemission, i.e., energy band dispersions can be mapped. Unoccupied electronic states play an important role, e.g., in ferromagnetism (minority spin states), in chemisorption (electron acceptor states of adsorbates), and for semiconductors (conduction by electrons). A status report is given of the mapping of bulk energy bands, and the observation of surface states. Recent data from SiO 2 are used to make the connection with luminescence.

Inverse Photoemission at Semiconductor Surfaces

Inverse photoemission is used as a novel probe for unoccupied electronic states. We observe unoccupied surface states on silicon and study their dependence on crystallographic orientation. Critical points of the conduction bands of bulk silicon are determined, e.g., L1 C at 2.30 eV and L3 C at 4.15 eV above the valence band maximum. New high-resolution data from cleaved GaP(110) surfaces show a surface state located at 0.3 eV below the conduction band minimum. For Pd2Si the density of unoccupied antibonding states is determined.