Determination of the energy band diagram for a-Si_1-xY_x:H/c-Si (Y = C or Ge) heterojunctions: Analysis of transport properties

Abstract

From current-voltage and photocurrent-voltage characteristics, the energy band diagrams of a-Si_1-xGe_x: H/c-Si, a-Si: H/c-Si and a-Si_1-x,C_x: H/c-Si heterojunctions have been determined. A comparison between the conduction band discontinuity δE_c, and the difference δE_g, between amorphous and crystalline optical bandgaps leads to a ratio δE_c/δE_g, equal to 0.66 ± 0.02 (a-Si_1-x,; H; E_g, = 1.90 eV), 066 ± 006) (a-Si:H; E, = 1·70eV), 0.79±0.04 (a-Si_1-x,Ge_x,:H; E_g,=1.48eV). A correlation is found between δE_c, and the difference E_c-E_f, between the amorphous conduction-band edge and Fermi level energies. Analysis of the current-voltage characteristics in the case of n- and p-doped crystalline substrates indicates a dominance of tunnelling mechanisms in most cases.