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

Electrical transport properties of our PECVD a-Si:H material has been improved by using hydrogen and/or helium dilution of silane and lower substrate temperature for deposition. For hydrogen-diluted material we have measured electron and hole mobilities approx.4 times larger, and μτ values 2-3 times higher than for our standard a-Si:H. The density of ionized dangling bonds (N_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 approx.90 MPa, while the electronic quality was kept as good as that of the standard material. By this technique 35 μm-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.