Simulation And Research Of Novel Semiconductor Devices For Radiation Detection

For decades,X rays and gamma rays play more and more important roles in medical applications, e.g. radiotherapy, computed tomography. It is in consequence imperative to develop novel dosimeters. The semiconductor dosimeters become an active area of research due to their small size, low power consumption, high sensitivity, capacity for integrated on a common chip with electric circuit and working without power supplied during irradiation. The conventional semiconductor dosimeters are mainly based on MOSFET(Metal-Oxide-Semiconductor Field-Effect Transistor) and FG-MOS (Floating Gate Metal-Oxide-Semiconductor Field-Effect Transistor) devices, the shifts of whose parameters,including threshold voltage and saturated drain current after irradiation, can be used to infer the adsorbed dose. In this thesis, the author introduce the advantages and disadvantages of conventional dosimeters, and propose three novel versions aim to solve the problems.Numerical simulations are performed with Sentaurus-TCAD and Silvaco-TCAD to discuss the feasibility of proposed devices for radiation detection.The first one is developed based on a SFGT (Semi Floating Gate Transistor), which embeds a large area PN diode between the floating gate and drain active region instead of thick oxide in conventional dosimeters as sensitive region to detect radiation. Simulation results show that SFGT device possesses the characteristics of high sensitivity and linearity,and its reset mechanism is more nondestructive and efficient compared with dosimeters base on MOSFET and FG-MOS devices. Extra simulations are carried out to study the effect of PN diode leakage current,which discharges the semi floating gate during the operation of reset even without irradiation. The results show that this device is suitable for applications with high dose rate irradiation.The second one is a SFGCD (Semi Floating Gate Controlled Camel Diode), whose reset mechanism is same with SFGT, while obtains higher sensitivity with smaller volume. The SFGCD device proposed by author for the first time incorporates the semi-floating gate into the camel diode. The irradiation simulations with SFGT device base on wide bandgap semiconductor SiC show that, the effect of PN diode leakage current is negligible.The last one is developed based on an AlGaN/GaN/AlGaN double-heterostructure HEMT (High Electron Mobility Transistor). An ultrahigh gain of readout current is obtained in simulations with optimized device structure, which overcomes the drawback of low X-ray absorption coefficient, showing the GaN based HEMT is extremely promising for future applications in fields ranging from high energy physics to medical imaging.The novel devices studied in this thesis have their respective advantages in compare with conventional devices for radiation detection, and are high suitable for medical applications.Moreover, these works provide certain reference significance for the further investigations of high-performance dosimeters.