Research On The Physical Model Of Millimeter‐wave GaN HEMT

As the third generation semiconductor material, Ga N has become an ideal semiconductor material for high-temperature and high-frequency micro-/millimeterwave semiconductor devices because of its particular properties such as large band gap, high breakdown voltage, high electron density and high electronic mobility,. In recent years, the application of Ga N-based high electron mobility transistors(HEMTs) in high frequency and large power output circuits has aroused broad interest among researchers and semiconductor companies. Their special attention is given on the Al Ga N/Ga N HEMT for its high breakdown voltage and high output power density. Though many researches have been made to explore the microwave Ga N HEMT models and the related device structure, the study focused on millimeter-wave Ga N HEMT is quite rare. This thesis aims at Al Ga N/Ga N HEMT physical modeling and field plate technology researching for millimeter-wave application. The main contents and innovations are as follows:Firstly, an Al Ga N/Ga N HEMT device with its gate length is 100 nm was chosen as the research object. A precise physical model was established with surface states, traps and self-heating effects taken into account. The simulation results are in good agreement with measured DC and RF characteristics. Then, the DC, RF, breakdown and thermal characteristics of the device were simulated and analyzed using the model.Secondly, the influence of the physical structure parameters on the device performance was studied. The results show that: increasing the gate-source distance will significantly reduce the saturated output current of the device; the gate-drain distance is increased to improve the breakdown voltage of the device, however, thus will result in lower cut-off frequency and higher knee voltage.At last, the application of field plate technology in millimeter-wave Al Ga N/Ga N HEMT was systematically studied. We not only analyzed the effects of gate field plate structure, source field plate structure and the gate-source double field plate structure on the increase of the breakdown voltage, but also further optimized the structure. The optimal modulation effect of electric field can be obtained when the length of the field plate was 0.2μm and the distance between the field plate and the barrier layer, and the breakdown voltage of the device to improve the most. The maximum breakdown voltages of the three structures were correspondingly 86 V, 74 V, and 92 V. The saturated output power density of the device can be improved as high as 38.5% by using the source-drain double field plate structure, but it may also seriously deteriorated the frequency characteristics of the device.In this paper, the TCAD was used to simulate the working mechanism of the millimeter-wave Ga N HEMT, predict device performance, and to optimize the design. It is instructive for millimeter-wave Ga N HEMT device physical modeling and structural optimization.