Influence Of Minority Carrier Lifetime On 4H-SiC N-IGBT

Silicon carbide(Si C) has received more and more attention as an attractive wide band gap semiconductor for developing high-power, high-temperature, and high-frequency devices. As a typical representative of high-voltage power switching devices, Si C Insulated Gate Bipolar Transistor(IGBT) has advantages of low on-resistance, simple gate drive, wide safety operation area and high operating frequency. Si C IGBT has a good developing prospect in the field of new applications such as the smart grid, electric vehicles, photovoltaic and wind energy and so on. As one of very important parameters to evaluate the quality of materials, the minority carrier lifetime plays a pivotal role in the optimized design of Si C IGBT. This dissertation mainly focus on the minority carrier lifetime and on-state and switching performance tradeoff of Si C IGBT. The main contributions of this dissertation are shown as follows:1. On-state, forward blocking and turn-off characteristics simulation of 4H-Si C n-IGBT have been studied. Based on the analysis of the operational principle and output characteristics of 4H-Si C n-IGBT, the model of asymmetric 4H-Si C n-IGBT with a buffer layer has been established using the simulator Sentaurus TCAD. The minority carrier lifetime is 2μs both in the drift region and buffer layer. The simulation results show that the blocking voltage of the device is high up to 11.7k V. A forward voltage drop of 5.36 V at 300A/cm2 is achieved with a gate bias of 15 V. The turn-off time is 130 ns and the turn-off loss is 4.62 m J/cm2.2. Optimized design of 4H-Si C n-IGBT with different buffer layer thickness has been investigated. The device structures with different buffer layer thicknesses are established, and the simulation and analysis of on-state characteristics and turn-off characteristics are given. Then the tradeoff curve of the forward drop and turn-off losses is obtained. The results show that the turn-off energy loss decreases by 75% with a buffer layer thickness of 10μm compared to 2μm.3. Influence of different minority carrier lifetime of the drift region and buffer layer on performance of 4H-Si C n-IGBT has been investigated. Based on requirements of Si C IGBT for minority carrier lifetime, local control of the lifetime in the drift region and buffer layer is conducted to optimize the power losses of the device. Analysis results show that the forward voltage drop decreases with increasing lifetime in the drift region. Simultaneously, the forward breakdown voltage and the turn-off tail current almost remain constant as the lifetime increases. The premise of this result is the same lifetime in the buffer layer. Similarly, under the condition of the same lifetime in the drift layer, the lower the lifetime in the buffer region is, the smaller turn-off tail current of the device will be, but the higher the forward voltage drop can be.4. Tradeoff between on-state and switching performance of 4H-Si C n-IGBT has been studied. For different lifetime in the drift region and buffer layer, the corresponding forward voltage drop and turn-off energy losses have been calculated. Finally, the tradeoff curve of forward voltage drop and turn-off energy losses at various lifetime parameters is obtained. It can be concluded the performance of 4H-Si C n-IGBT while the lifetime in the drift region and in the buffer layer and buffer is 8μs,0.08~0.1μs,respectively. At the optimum parameters, the forward voltage drop is 5.13 V and turn-off loss is as low as 0.8~1.1m J/cm2.The turn-off loss decreases 3.5~3.8m J/cm2 compared to non-optimized device. The on-state and switching performance tradeoff of the device has been realized.Simulation results in this paper show that the tradeoff between on-state and switching performance of 4H-Si C n-IGBT has been improved by local control of the lifetime in the drift region and buffer layer. The research provides a basis for the further optimization design of Si C IGBT.