METAL/N-INP INTERFACES STUDIED BY PHOTOREFLECTANCE AND RAMAN SPECTROSCOPIES

We report electrical and optical studies of metal/n-InP interfaces formed at room temperature (RT = 300 K) and low temperature (LT = 77 K). From current-voltage (I-V) and capacitance-voltage (C-V) data, it was found that the leakage current density, J0 of the LT diode was reduced by more than six orders of magnitude with respect to the RT diode. The Schottky barrier height, phi(B) was increased from 0.44 to 0.83 eV with Pd metal. This suggested Fermi-level unpinning in the LT diodes, Better surface preservation was revealed by photoreflectance spectroscopy (PR) measurement. The surface electric field, xi built-in potential, V(bi) and broadening parameter, GAMMA were also determined from PR spectra. These results were further related to Raman spectra, in which both the LO phonon mode from the depletion layer, and the coupled plasmon mode, L+ from the bulk were observed. The intensity of the LO mode increased with the width of the depletion layer. The Raman shift of the L+ was sensitive to the carrier density in the bulk region. The relative intensity of LO and L+ was used to compare the width of the depletion layer for RT and LT samples. Very good agreement was obtained between the electrical and optical results,