Alternative doped a-Si1−xCx:H and nc-Si1−xCx:H films

Abstract

Conductive amorphous and nanocrystalline films were prepared from gas mixtures containing the dopant vapor (P(CH3)3 or B(C2H5)3), silane and hydrogen by use of a λ/4 helical resonator plasma source operating at 40 MHz. Film microstructure was observed by atomic force microscopy (AFM) and ultraviolet reflectometry. Secondary ion mass spectrometry (SIMS) and electron probe micro analysis (EPMA) was used to investigate the film composition. Measurements of transmission and reflection were done to determine the film thickness, refractive index and the Tauc optical gap. The maximum dark conductivity was about 0.5 to 1 S/cm with an activation energy of about 50 meV. Dangling bond densities were estimated by constant photocurrent method (CPM). Electron and hole diffusion lengths determined by the dynamic interference grating (DIG) method are found to be sensitive to the type of conductivity and to the density of dangling bonds. A two-color sensor with a n-i-p-i-n layer sequence was fabricated as an illustration to the application of the alternative doping technique based on liquid sources P(CH3)3 and B(C2H5)3.