DETERMINATION OF THE ENERGY-BAND DIAGRAM FOR A-SI1-XYX-H/C-SI (Y = C OR GE) HETEROJUNCTIONS - ANALYSIS OF TRANSPORT-PROPERTIES

From current-voltage and photocurrent-voltage characteristics, the energy band diagrams of a-Si1-xGex:H/c-Si, a-Si:H/c-Si and a-Si1-xCx:H/c-Si heterojunctions have been determined. A comparison between the conduction band discontinuity DELTA-E(c), and the difference DELTA-E(g) between amorphous and crystalline optical bandgaps leads to a ratio DELTA-E(c)/DELTA-E(g) equal to 0.66 +/- 0.02 (a-Si1-xCx:H; E(g) = 1.90 eV), 0.66 +/- 0.06) (a-Si:H; E(g) = 1.7) eV), 0.79 +/- 0.)4 (a-Si1-xGex:H; E(g) = 1.48 eV). A correlation is found between DELTA-Ec 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.