Critical Energies of Photoreflectance and Lineshape Analysis of Photoluminescence of Heavily Si-Doped GaAs

Room temperature photoluminescence (PL) and photore-flectance (PR) spectra of heavily Si-doped GaAs grown by molecular beam epitaxy (MBE) were investigated as a function of electron concentration and compared with each other. It was found that for highly degenerate semiconductors the critical energy measured by the PR equals to the peak energy of the PL spectrum. When Fermi level lies below the conduction band minimum, the PR spectra revealed the band gap energy as well as the energy E_max at which the electron concentration per unit energy in the donor band becomes maximum, and this maximum was observed to merge in the conduction band at about 3 x 10¹⁷ cm ^-3 electron concentration. And from the line-shape analysis of the PL spectra, it was found that the conduction band tail η_c and the Fermi energy ε _f measured from the conduction band mmimum can be expressed as η_c = 2.0 x 10^-8 n ^1/3(eV) and ε _f = —0.074 + 1.03 x 10^-7 n ^⅓(eV), respectively.