Investigation On Characteristics And Current Collapse Of InAlN/GaN HEMTs

As a respresentative of the third generation of semiconductor, GaN, has lots of advantages such as wide band-gap,high breakdown voltage, saturation velocity, chemical stability,radiation resistance and so on. These advantages make GaN become an ideal material for high-temperature, high-power and high-frequency devices. Even though much progress has been achieved in AlGaN/GaN HEMTs, there are still some issues need to be improved, such as current collapse. As a new type of material, InAlN has attracted much attention recently. The InAlN material can be grown on GaN plate with lattice matched when the indium content close to 17%, thus improving the HEMTs reliability operating under the high-temperature and voltage conditions. However, due to the phase separation and composition inhomogeneity, it is very difficult to grow InAlN ternary alloy with high quality, which impedes the realization of its vast application. Until now few studies have been carried out on the reliability of InAlN/GaN HEMTs during the past years, and it is still in initial stage at home. In this dissertation, the DC characteristics of InAlN/GaN HEMTs were studied in detail based on the experiments and simulations and the focus is on the current collapse.Firstly, high electric field degradation phenomena were investigated under OFF-state and ON-state conditions. Under both of the conditions, obvious degradation, which consists of the saturation drain current and maximal transconductance has been observed. The simulation result shows that it would take a long time to recover from the degradation. The degradation of InAlN/Ga N HEMTs was more serious with increasing the high-field stress voltage and the stress time. Based on the analyses of the simulation and experimental results, we concluded that the perfommance degradation under OFF-state condition are caused by the electrons filling in surface states emmited from gate electrode at high gate-to-drain electric field. However,the channel hot electrons are suggested to play major roles in th ON-state degradation.Gate pulsed I-V characteristics were also measured. It is found that the shorter the pulse width was, the lower the drain current. By analyzing the results, we found that trap effect is still the main reason of current collapse under pulse and RF signal conditions. Under these conditions, the charge and discharge speed of the surface state and barrier layer traps can't catch up with the input signal.By utilizing the two-dimensional device simulation software Atlas, simulations of In AlN/GaN HEMT have been carriered out finally, and the effects of structural parameters on the electrical properties were analyzed. Moreover, by incorporating traps into the surface of InAlN/GaN HEMTs, the current collapse and its recover process were simulated. The simulation results verified the correctness of the conclusion.