Improved mobility-lifetime product of holes in a-Si:H n-i-p devices: A consequence of structural relaxation?

The influence of He dilution high deposition rate (×10) conditions on the optical, structural and transport properties of plasma enhanced chemical vapor deposited a-Si:H is investigated on n-i-p diodes. The hole drift length is measured on these devices through a simple steady state method. The mobility-lifetime product of holes is shown to be 2.5 times higher in the sample prepared in He dilution conditions than in the standard sample. This significant increase is associated with lower absorption coefficients in the sub-band-gap range (≈ ×0.25), higher hydrogen (×1.6) and lower oxygen (×10^-2) contents, and a better relaxed, partially crystallized, structure.