【作者】 刘芳；

【导师】 王涛； 姚建铨；

【作者基本信息】 天津大学 ， 物理电子学， 2010， 博士

【摘要】 AlxGa1-xN/GaN异质结构材料和器件的研究是当前研究的前沿领域和热点。而其中热点研究之一是肖特基接触的研究。本文系统的研究了在Ni/Au金属和GaN间插入3nm薄Al层这种新型结构肖特基接触的热稳定性,同时研究了在Ni/Au金属与Al0.25Ga0.75N/GaN异质结间插入3nm薄Al层肖特基接触的反向漏电机制,以及Ni/Au肖特基接触的高温电流输运机制。本文最后研究了用金属W的氮化物作为Al0.25Ga0.75N/GaN的肖特基接触的热稳定性。主要研究结果如下:(1)研究了在Ni/Au和GaN间插入一个3nmAl薄层的肖特基接触的电学性质和热稳定性。发现Al薄层的插入不仅将肖特基接触的反向漏电减小了几乎两个数量级,而且提高了肖特基接触的热稳定性。研究了Al/Ni/Au肖特基接触的热退火性质,我们发现在插入Al薄层后,势垒高度和串联电阻在退火温度低于4500C时,随温度的上升逐渐增加。我们也得到Al/Ni/Au肖特基结在退火温度为4500C,退火时间为12分钟时,反向漏电最小。(2)研究了传统Ni/Au肖特基与Al0.25Ga0.75N表面之间插入了3nm的Al薄层后肖特基接触在温度为25-3500C之间时的反向漏电情况,并且和未插薄Al层的肖特基接触进行了比较。实验结果表明插入薄铝层后,I-V曲线的最低点向负偏压方向移动。随着温度的上升,该点又回到零点。反偏漏电对温度的依赖也被研究。结果表明Al薄层的插入在Al0.25Ga0.75N和金属之间引入了界面态。插入的Al与Al0.25Ga0.75N表面的氧杂质反应,减小了氧元素引起的缺陷,同时形成了Al2O3绝缘层,抑制了与氧有关的隧穿电流和热场发射电流。而且Al的插入也提高了二极管的高温可靠性。在研究新型肖特基接触的同时还研究了Au/Ni/Al0.25Ga0.75N/GaN肖特基二极管在250C-2500C温度范围内的电流输运机制,发现肖特基势垒高度的高斯分布模型能很好的解释在该温度范围内有效肖特基势垒随温度升高而升高的实验结果。(3)研究了N2气与Ar气比例不同时WNx/Al0.25Ga0.75N/GaN异质结肖特基接触的热稳定性。以及用肖特基势垒的高斯分布模型拟合了WNx肖特基接触的电流输运机制。本文用在N2和Ar的混合气体中磁控溅射纯W靶得到了WNx材料,发现当N2比例不同时,WNx肖特基接触的热稳定性和反向漏电情况不同。实验发现当N2:Ar气的比例为1:2时,WNx肖特基接触可以稳定到6000C;当N2:Ar的比例为4:1时,WNx肖特基接触可以稳定到5000C,且反向漏电可以达到10-6A/cm2。更多还原

【Abstract】 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.更多还原