A Study Of AlGaN/GaN HEMT Switching Power Device And Modeling

As the third-generation semiconductor, wide bandgap material GaN has some electrical properties better than those of Si. High electron mobility transistor(HEMT) based on AlGaN/GaN heterostructure is able to adapt to high temperature, high voltage, high frequency and high power applications. AlGaN/GaN HEMT is ideal for new power semiconductor device. But AlGaN/GaN HEMT as a power device has a series of problems needed to be solved, such as improvement of breakdown voltage, achievement of enhancement-mode device and so on. In this paper, exploration and research have been conducted upon some of these issues, mainly as follows:1. Based on relevant references, an introduction of major processes of depletion-mode AlGaN/GaN HEMT is made and process steps of tapeout experiment determined, including Ohmic contact, device isolation, Schottky contact, metal trace, passivation dielectric layer, field plate metal and thick metal. Layout of device is drawn and tapeout experiment conducted according to the process. Transfer characteristics, output characteristics and breakdown characteristics are analyzed based on the test results, particularly the influence of the gate-source and gate-drain spacing on electrical property of the device. The maximum drain saturation current of the device reaches 730mA/mm and the breakdown voltage is greater than 100 V at the gate-source spacing of 1.5μm.2. Two common methods of achieving enhancement-mode AlGaN/GaN HEMT--recess gate and negative charges implanted into gate region are studied by computer simulation. The variation with recess depth and density of negative charges of transfer characteristics of the device is analyzed. An enhancement-mode AlGaN/GaN HEMT threshold voltage analytical model is built. By studying the bandgap structure of gate region at equilibrium and adding the influence of surface state charges on threshold voltage, the analytical formula of threshold voltage of enhancement-mode device is acquired. Simulation result of threshold voltage of the device is 0.87 V and model result is 0.58 V at the recess depth of 20 nm. Simulation result of threshold voltage of the device is 1.95 V and model result is 1.99 V at the density of negative charges of 1.05×1019cm-3. Model results are compared with simulation results with that match and enhancement-mode device achieving. An electric field-induced tunneling enhancement-mode AlGaN/GaN HEMT is proposed and working principle and fundamental performance of the device are analyzed.