Research Of New Structures And New Material Of Schottky Contacts On GaN-based Devices

AlxGa1-xN/GaN heterostructure materials and devices have attracted a lot of interests.In this work, We have systematically investigated the Thermal annealing behaviour of Al/Ni/Au multilayer on n-GaN Schottky contacts and the leakage current mechanisms in the Schottky diode with a thin Aluminium layer insertion between Al0.25Ga0.75N/GaN heterostructure and Ni/Au Schottky contact.And the current transport mechanism in Au/Ni/Al0.25Ga0.75N/GaN Schottky diodes has been investigated.At last, Thermal annealing behaviour of WNx/Al0.25Ga0.75N/GaN Schottky diodes has been studied. The main results are as follows:(1) We investigated the effects of the insertion of a thin Aluminium layer into the boundary of the GaN surface and Ni/Au Schottky gate metal on the electrical characteristics of GaN diodes. In the Shottky diodes with a thin Aluminium layer, the gate leakage current is reduced by two orders of magnitude.The thermal annealing behaviour is improved. Then Thermal annealing behaviour of Al/Ni/Au on n-GaN Schottky contacts was investigated. It was found that the barrier height and the serial resistance increase with the annealing temperature below 4500C. And the thermal anneal temperature is 12 minutes at 4500C, the reverse-bias current is the lowest in Au/Ni/Al/GaN diode.(2) We investigated the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer insertion between Al0.25Ga0.75N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25-3500C. And we compare with the Schottky diode without Aluminium inserting layer. The experimental results show in the Schottky diode with Aluminium layer the minimum point of I-V curve drifts to the minus voltage, and with the temperature increasing, the minimum point of I-V curve returns the 0 point. The temperature dependence of gate-leakage current in the novelty diode and the traditional diode is studied. The results show that the Aluminium inserting layer introduces interface states between metal and Al0.25Ga0.75N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Aluminium layer.At the same time, the current transport mechanism in Au/Ni/AlGaN/GaN Schottky diodes has been investiged between 250C-2500C.Thermionic-emission model with a Gaussian distribution of SBHs is thought to be responsible for increasing of the SBHs with increasing temperature. (3) The effect of thermal annealing of WNx/Al0.25Ga0.75N/GaN structures hasbeen studied when the proportion of N2 to Ar is changed.Thermionic-emission model with a Gaussian distribution of SBHs is thought to be responsible for the current transport mechanism in WNx Schottky contacts.WNx is formed by reactive sputtering from a pure W target in an Ar-N2 gas misture.It is found that the thermal anealing and gate leakage changed with changing the proportion of N2 to Ar . The thermal stably temperature is 6000C when the proportion of N2 to Ar is 1:2. The thermal stably temperature is 5000C and the gate leakage is about 10-6A/cm2 when the proportion of N2 to Ar is 4:1.