Optimized Design Of Enhanced GaN HEMT With P-GaN Gate And Trench Gate Structure

Compared with Si materials,GaN materials have higher critical breakdown electric field and electron saturation speed than Si materials,so under the same size,GaN-based devices have higher breakdown electric field and power density and lower switching power loss than Si-based devices.Therefore,GaN-based devices have become a strong competitor of traditional Si-based devices in many fields.However,another disadvantage brought by the polarization effect of GaN materials is that GaN-based HEMTs are normally-on devices(threshold voltage is less than zero),which not only increases the compatibility with existing common circutis but also increases the turn-off loss of the devices.Therefore,the research and design of enhancement mode GaN-based devices has become the key to solve the above-mentioned problems.Nowadays,there are many ways to realize the design of enhanced GaN-based devices.Among them,P-GaN gate is widely used because of it's good reliability.However,the traditional P-GaN gate structure can only make GaN-based devices have a threshold voltage of about 1V,which is difficult to meet the needs of many applications.So,this paper started from increasing the threshold voltage of GaN-based devices,and successfully designed an enhanced HEMT with a high threshold voltage by using the P-GaN gate combined with the trench gate structure.In addition,a double heterojunction buffer layer and a field plate structure were used to effectively increase the breakdown voltage of the device.The research results obtained are summarized as follows:(1)The design of the buffer layer structure was carried out,adopted the double heterojunction buffer layer structure,and compared with the single heterojunction buffer layer structure,the breakdown voltage was increased by nearly 33%.(2)The influence of the P-GaN gate doping concentration on the threshold voltage of the device was studied.By changing the P-GaN gate doping concentration,an effective P-GaN gate doping with enhanced design was obtained and the impurity concentration was3?10^{1 7}cm^-3.In addition,the paper used the P-GaN gate combined with the trench gate structure and studied the relationship between the trench gate etching depth and the device threshold voltage,achieved a threshold voltage up to 3.4V;By changing the gate width and the distance between the gate and the drain,a maximum breakdown voltage of 814V was abtained.(3)The influence of barrier layer Al composition and barrier layer thickness on the threshold voltage and on-resistance of the device were studied.By changing the size of the Al composition and the thickness of the barrier layer,a minimum on-resistance of9.6W×mm and a maximum saturation current of 1.5?10^-4A×mm were obtained.(4)Analyzed the types and principles of the field plates,added gate field plate and studied the influence of the length of the gate field plate and the thickness of the dielectric layer under the field plate on the device threshold voltage,and the breakdown voltage was increased to 851V compared with the non-field plate structure;used the gate field plate combined with the drain field plate structure,the influence of the gap between the gate field plate and the drain field plate on the device breakdown voltage was studied,and the breakdown voltage was further increased to 863V compared with single gate field plate.