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, φ_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, ξ built-in potential, V_bi and broadening parameter, Γ 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.