CONCENTRATION-DEPENDENT NEAR AND ABOVE BAND-EDGE ABSORPTION IN DOPED INP AND ITS EFFECT ON SOLAR-CELL MODELING

Absorption coefficients for n- and p-type InP are reported for the fir st time in the energy range of 1.3-3.0 eV in this paper. In order to o btain absorption coefficients in the higher energy range of 1.8-3.0 eV , extremely thin (-0.2 mu m) InP samples were fabricated and bonded to glass substrates. For measurements in the lower energy range of 1.3-1 .6 eV, samples with thickness in the range of 0.5-0.9 mu m were found to be optimum. For energies below 1.6 eV, the absorption coefficients are a strong function of the doping concentration. However, in the ene rgy range of 1.8-3.0 eV there is little doping dependence and the meas ured absorption coefficients follow the theoretical calculations. In t he case of n-type samples, absorption coefficients decrease with incre asing doping concentration and the absorption edge moves to higher ene rgy due to the Burstein-Moss effect. For p-type samples, the absorptio n edge shifts to lower energies due to transitions between band tails. Model calculations show that the use of accurate doping-dependent abs orption coefficients reported in this paper, as opposed to the commonl y used absorption coefficients of undoped InP, can result in significa nt improvement in the predicted internal quantum efficiency and device parameters of InP solar cells. (C) 1995 American Institute of Physics .