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Development of radiation detectors based on hydrogenated amorphous silicon and its alloys

Description: Hydrogenated amorphous silicon and related materials have been applied to radiation detectors, utilizing their good radiation resistance and the feasibility of making deposits over a large area at low cost. Effects of deposition parameters on various material properties of a-Si:H have been studied to produce a material satisfying the requirements for specific detection application. Thick(-{approximately}50 {mu}m), device quality a-Si:H p-i-n diodes for direct detection of minimum ionizing particles have been prepared with low internal stress by a combination of low temperature growth, He-dilution of silane, and post annealing. The structure of the new film contained voids and tiny crystalline inclusions and was different from the one observed in conventional a-Si:H. Deposition on patterned substrates was attempted as an alternative to controlling deposition parameters to minimize substrate bending and delamination of thick a-Si:H films. Growth on an inversed-pyramid pattern reduced the substrate bending by a factor of 3{approximately}4 for the same thickness film. Thin (0.1 {approximately} 0.2 {mu}m) films of a-Si:H and a-SiC:H have been applied to microstrip gas chambers to control gain instabilities due to charges on the substrate. Light sensitivity of the a-Si:H sheet resistance was minimized and the surface resistivity was successfully` controlled in the range of 10{sup 12} {approximately} 10{sup 17} {Omega}/{four_gradient} by carbon alloying and boron doping. Performance of the detectors with boron-doped a-Si:C:H layers was comparable to that of electronic-conducting glass. Hydrogen dilution of silane has been explored to improve electrical transport properties of a-Si:H material for high speed photo-detectors and TFT applications.
Date: April 1, 1995
Creator: Hong, Wan-Shick
Partner: UNT Libraries Government Documents Department

Thick amorphous silicon layers suitable for the realization of radiation detectors

Description: Thick silicon films with good electronic quality have been prepared by glow discharge of He-diluted SiH{sub 4} at a substrate temperature {approximately} 150{degree}C and subsequent annealing at 160{degree}C for about 100 hours. The stress in the films obtained this way decreased to {approximately} 100 MPa compared to the 350 MPa in conventional a-Si:H. The post-annealing helped to reduce the ionized dangling bond density from 2.5 {times} 10{sup 15} cm{sup {minus}3} to 7 {times} 10{sup 14} cm{sup {minus}3} without changing the internal stress. IR spectroscopy and hydrogen effusion measurements implied the existence of microvoids and tiny crystallites in the material showing satisfactory electronic properties. P-I-N diodes for radiation detection applications have been realized out of the new material.
Date: April 1, 1995
Creator: Hong, Wan-Shick; Drewery, J.S.; Jing, Tao; Lee, Hyong-Koo; Perez-Mendez, V. & Petrova-Koch, V.
Partner: UNT Libraries Government Documents Department

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

Description: Electrical transport properties of the authors 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 they have measured electron and hole mobilities {approximately} 4 times larger, and {mu}{tau} values 2-3 times higher than for their 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 {approximately}90 MPa, while the electronic quality was kept as good as that of the standard material. By this technique 35 {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.
Date: November 1, 1994
Creator: Hong, Wan-Shick; Drewery, J. S.; Jing, Tao; Lee, Hyoung-Koo; Kaplan, S. N.; Perez-Mendez, V. et al.
Partner: UNT Libraries Government Documents Department