|M.Sc Student||Borukhin Shirly|
|Subject||Radiation Induced Electron Generation and Transport in|
Diamond Thin Films
|Department||Department of Materials Science and Engineering||Supervisors||Professor Emeritus Yeshayahu Lifshitz|
|Professor Emeritus Rafael Kalish|
In this research polycrystalline diamond films grown by CVD are investigated as alpha radiation detectors. The pCVD films can be grown on large areas, with controlled thickness and with high reproducibility. However, when used for the fabrication of radiation detectors, several drawbacks have to be considered: the grain boundaries of pCVD diamond films introduce defect states in the electronic band gap that account for the reduction of the total charge collection of the detector (decreased efficiency). The charge trapped during detector operation creates an internal field (polarization) which affects the detector signal and causes instability of the signal with operation time.
The objectives of this thesis are to increase the detection efficiency of thin pCVD diamond detectors, and to find ways to maintain stability of the detector pulse during the irradiation time.
Intrinsic pCVD films of different film thicknesses were grown, and the effect of thickness on the pulse stability was examined. The effect of the a irradiation penetration depth in thin pCVD diamond films was also tested by lowering the radiation energy, using an absorber (Mylar) that was attached to the front side of the detector. Detectors with film thickness of the order of the radiation penetration depth demonstrated high stability, while those with a thickness larger than the radiation range exhibited polarization (i.e. their efficiency decreased with operation time).
Bi-layered films, made of a B-doped CVD layer grown on top of Si substrate and an intrinsic CVD layer above it, were fabricated. The B doping of the first diamond layer grown on the Si substrate was performed in order to reduce the effect of the poor crystalline quality of the Si-diamond interface, thereby to improve the intrinsic pCVD bulk quality. The addition of the B-doped layer was shown to increase the detection efficiency and to suppress polarization (when positive bias is applied to the substrate and the upper surface is grounded).