Soft X-Ray Emission and Resonant Inelastic Soft X-Ray Scattering on InP

We present studies of the local partial density of states (LPDOS) on InP measured by soft x-ray emission spectroscopy (SXE) and specific investigations of the band structure E(k) by resonant inelastic x-ray scattering (RIXS)[1]. In both techniques, a core hole is created by promoting an electron into unoccupied states and the fluorescence originating from the filling of this core vacancy by a valence electron, is measured. In SXE the electron is excited far above the absorption threshold. As a result, the fluorescence maps the LPDOS. In RIXS, on the other hand, the excitation energy is tuned in small steps over the absorption threshold. In this case absorption and emission must be seen as a scattering process, leading to a valence electron-hole pair in the final state. Momentum conservation ensures that the electron and the hole in the final state have the same crystal momentum. Hence, RIXS includes information on the wavevector and the band structure E(k). While SXE is probing the whole Brillouin zone, it is possible to selectively investigate parts of the Brillouin zone by RIXS. The excitation energy determines which parts of the Brillouin zone are probed. The measurements were performed using a grazing incidence Rowland spectrometer set to a resolution of 300 meV. Due to the high flux and resolution of the BW3 undulator beamline at HASYLAB, DESY, it was possible to tune the excitation energy in steps of 100 meV over the absorption threshold to observe the excitation dependance in the RIXS. In figure 1 we present the P(s+d)-DOS as measured by P 2p SXE (solid line) in comparison with the calculated total DOS (dashed line)[2]. Experiment and calculation are in good agreement when taking into account that because of the dipole selection rule the experimental data represent the s- and d-type LPDOS. While the lower VB is dominated by d-type states, the upper VB contains s and p hybridized states and appears thus weaker in the experiment