Study Of A Linear Al_xGa_1-xN/AlN/Al_yGa_1-yN/GaN HEMT With Submiron And Modeling

AlGaN/GaN high electron mobility transistor (HEMT) has become a promising device for a new generation of wireless communication and power amplifier in military application. Since the birth of AlGaN/GaN HEMT, GaN based material and devices with Wide-Band Gap have thrived. By the great development of the material quality and devices processing technic, AlGaN/GaN HEMT has been much improved in both DC and RF performance, also the part of device application. But there is lots of problem require urgent settlement, for example, We understand GaN less than Si, GaAs, et al. So the device can improve so much more in performance. Conventional AlGaN/GaN HEMT has its limitations, such as the linearity, when develping AlGaN/GaN HEMT devices in high frequency and large power application. We need to research a better device structure to improve the devices'performance better. In other hand, because the GaN based devices are youthful, we have less research achievement in both large signal and small signal model theory of AlGaN/GaN HEMT, and we lack accurate models.Optimizing the epitaxial layer of AlGaN/GaN HEMT, especially the channel region, has caused our concern in recent years. At present, the research about inserting an AlGaN layer with low Al component in AlGaN/GaN HEMT has been done. The results show Al_xGa_1-xN/Al_yGa_1-yN/GaN composite channel HEMT (CC-HEMT) could improve the linearity of device effectively. The paper will design a novel device on that basis, then extracting Parasitics and producing large signal model. The main research work done includes the followings:First, We start from the principal about band theory and carrier transform of AlGaN/GaN HEMT and calculate the property such as two dimensional electron gas concentration distribution and electric field distribution and so on by self-consistently solving Poisson Equation and Fermi distribution. Design essentials of each epi-layer in HEMT were analyzed, such as the thickness of barrier layer, the thickness of channel layer and the component of Al were changed to find their effect on the device characteristics. Then Silvaco TCAD was used to simulate the I-V characteristics of AlGaN/GaN HEMT. The best epitaxy structure is Al_0.27Ga_0.73N/AlN/Al_0.04Ga_0.96N/GaN HEMT, with the thickness of barrier layer 22nm and the thickness of composite channel layer 8nm. The simulation results of the device with 0.3μm gate length and 100μm gate width show a less change of transconductance when the gate voltage changed from -4V to -2.5V. It means good linearity for HEMTs in submicron structure. Also we simulate the heating effect of this device structure.Then we design a series of devices with defferent size for modeling reasons and make the sample. The novel devices show better linearity than conventional devices, which is processed in the same technological conditions, by comparing the DC, small signal and large signal property. Comparing the testing results and the simulating results, it shows the theory analysis and simulatin results have clear guiding significance, which could reduce the developmental cost of time and money, avoiding design devices'stucture blindly.Finally, the HEMT equivalent circuit models were introduced starting with the small signal analysis. We analysis the method about extracting parasitics, and give the detailed procedures in extracting both parasitic elements and intrinsic elements. And we produce the large signal model of device by EEHEMT1 model. The verification experiment proves that this model could meet with the request to precision.