HIGHLY PHOTOSENSITIVE HELIUM DILUTED AMORPHOUS-SILICON 1.5 EV BAND-GAP - ROLE OF PRESSURE

Highly photosensitive low band gap (≥1.5 eV) hydrogenated amorphous silicon (a-Si:H) films have been developed by plasma enhanced chemical vapor deposition using helium dilution of the process gas, silane at substrate temperature 210°C. Low band gap of a-Si:H films is achieved by reducing bonded hydrogen content and hence by increasing compactness of the films. At the optical gap ∼1.5 eV, a-Si:H film has high mobility lifetime product, ημτ (8×10-5 cm-2V-1) and photosensitivity (≳7×104) values. The defect density of the material is as low as 7.8×1015 cm-3eV -1 and hydrogen content is 4.54 at.%. Low band gap amorphous silicon germanium (a-SiGe:H) films reported so far do not have such high ημτ and photosensitivity values at 1.5 eV optical gap. Thus, this low band gap a-Si:H films can be used as intrinsic layer in the bottom cell of a multijunction solar cell replacing a-SiGe:H alloy films. © 1995 American Institute of Physics.