Charged particle detectors based on high quality amorphous silicon deposited with hydrogen or helium dilution of silane

Abstract

The electrical transport properties of our PECVD a-Si:H material has been improved by using hydrogen and/or helium dilution of silane and a lower substrate temperature for deposition. For hydrogen-diluted material we have measured electron and hole mobilities /spl sim/4 times larger, and /spl mu//spl tau/ values 2-3 times higher than for our standard a-Si:H. The density of ionized dangling bonds (N/sub D/*) also showed a factor of 5-10 improvement. Due to its higher conductivity, the improved a-Si:H material is more suitable than conventional a-Si:H for TFT applications. However, it is difficult to make thick layers by H-dilution because of high internal stress. On the other hand, thick detectors can be made at a faster rate and lower stress by low temperature deposition with He-dilution and subsequent annealing. The internal stress, which causes substrate bending and delamination, was reduced by a factor of 4 to /spl sim/90 MPa, while the electronic quality was kept as good as that of the standard material. By this technique 35 /spl mu/m-thick n-i-p diodes were made without significant substrate bending, and the electronic properties, such as electron mobility and ionized dangling bond density, were suitable for detecting minimum ionizing particles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>