论文标题:高耐压功率GaAs MESFET的研究与制备
Study and Fabrication of the High Breakdown Voltage Power GaAs MESFET"s
论文作者 陈宏江
论文导师 杨瑞霞；武一宾,论文学位 硕士,论文专业 微电子学与固体电子学
论文单位 河北工业大学,点击次数 100,论文页数 52页File Size5510k
2005-01-01论文网 http://www.lw23.com/lunwen_988632937/ 砷化镓金属-半导体场效应晶体管;栅漏击穿电压;低温GaAs;双晶X射线衍射仪;选择湿法腐蚀;原子力显微镜;传输线模型;比接触电阻
GaAs metal-semiconductor field effect transistor; Gate-Drain breakdown voltage; low temperature GaAs; double-crystal X-ray diffractometer; selective wet etching; atomic force microscopy; transmission line model; contact resistivity
砷化镓(GaAs)金属—半导体场效应晶体管(MESFET)是一种重要的GaAs器件,广泛的应用于无线通讯、信息技术和相控阵雷达等众多领域。栅漏击穿电压(BV_(gd))是GaAs MESFET的重要性能指标之一。目前国内GaAs MESFET的栅漏击穿电压只略高于10V,限制了GaAs MESFET的输出功率。提高BV_(gd),改善GaAs MESFET功率特性,成为当今众多学者的重要研究内容。 本文分析了GaAs MESFET的击穿机理,设计了非掺杂低温(LT)GaAs作为帽层,AlAs作为隔离层的高击穿电压GaAs MESFET器件结构。进行了LT GaAs材料生长、GaAs/AlGaAs选择湿法腐蚀、源漏欧姆接触等一系列研究实验。打通了制备工艺,制备出了高击穿电压的GaAs MESFET器件。 用分子束外延(MBE)设备在不同温度下生长了LTGaAs材料,并进行了600℃的退火实验。分别用双晶X射线(X-Ray)衍射仪和霍尔(Hall)测试系统测试了LT GaAs退火前后的结构特性和电学特性。结果表明:生长温度越低,LT GaAs的晶格常数越大;180℃生长的LT GaAs材料退火后电学特性较好,电阻率为4×10~(17)Ω·cm,呈半绝缘特性。 进行了50%柠檬酸溶液和30%5双氧水溶液按体积比从1:1到10:1,Al_xGa_(J-x)As中的Al组分分别为x=0.2、0.3、1.0的选择湿法腐蚀实验。用α台阶仪、原子力显微镜(AFM)测试了不同体积比和不同Al组分时的腐蚀速率和样品表面形貌。结果表明:随着腐蚀液体积比的增大,溶液对AlGaAs的腐蚀速率呈上升趋势,而对GaAs的腐蚀速率呈先升后降趋势;腐蚀速率越大,腐蚀后的GaAs表面越粗糙,AlGaAs中Al的组分越大,腐蚀后的AlGaAs表面越平。分析了选择腐蚀机理,确定了腐蚀工艺中50%柠檬酸:H_2O_2=1.5:1的最佳腐蚀液配比方案。 用50%柠檬酸/H_2O_2溶液腐蚀掉GaAs MESFET材料的LT GaAs帽层,用盐酸漂掉AlAs自停止层,在掺杂浓度为1×10~(17)cm~(-3)的有源沟道层上做了欧姆接触合金实验。用探针台测得不同合金工艺条件下的接触电阻值,建立传输线(TLM)模型,计算了欧姆接触的比接触电阻。选出了450℃,90s的最佳合金条件。 最后利用所做实验的结论制备了输出功率大于500mW,工作频率为4HGz时,增益不
GaAs MESFET is a kind of important GaAs device. They have been widely used in wireless communications, information technologies and phase array radars etc. Gate-Drain breakdown voltage(BVgd) is one of the important parameters of GaAs MESFET. Presently, the BVgd of domestic GaAs MESFET is only more than 10V, which limits the output power of GaAs MESFET. Improving the BVgd and meliorating the power characteristics have become the important field focused by researchers.In this thesis, we analyse the breakdown mechanism of GaAs MESFET"s, and design the structure of high breakdown voltage GaAs MESFET with a undoped LT GaAs cap layer and a AlAs spacer layer. A series of experiments including material growth, selective wet etching and ohmic contact were carried out, and than the high breakdown voltage GaAs MESFETs were fabricated.Molecular Beam Epitaxy (MBE) LT GaAs materials were grown at different substrate temperature. The annealing experiments of LT GaAs were carried out at 600 ℃. Before and after annealing, the structure characteristics have been tested with double-crystal x-ray diffractometer, and the electric characteristics have been obtained with Hall testing system. The results show that the lower the growth temperature is, the bigger the crystal lattice constant is. The annealed GaAs layer grown at 180℃ is semi-insulating and has better electric characteristics. Theresistivity of the annealed GaAs layer is 4×107Ω cm.The volume ratio of 50% citric acid solution to 30% H2O2 was changed from 1:1 to 10:1. and the selective wet etching experiments of GaAs over AlxGa1-xAs(x=0.2,0.3,1.0) were carried out. We used a-step instrument and the atom force microscopy (AFM) to study the etching rate and the surface of the different Al mole fraction samples etched with the solution of different volume ratio of 50% citric acid solution to 30% H2O2. The results indicate that the etching speedof AlxGa1-xAs increases with the ratio increase, and the etching speed of GaAs increases first with the increase in the ratio and than decreases with the further increase in the ratio. The bigger the speed of etching is, the rougher the GaAs surface is. The larger the Al mole fraction of AlxGa1-xAs is , the smoother the AlxGa1-xAs surface is. The mechanism of the selective etching was analysed. It was confirmed that the optimum volume ratio of 50% citric acid solution to 30% H2O2 is 1.5 : 1.The LT GaAs cap layer of GaAs MESFET was etched off with the 50% citric acid/H2O2 solution, and the AlAs spacer layer with hydrochloric acid. The alloying experiments were carried out on GaAs active layer which doped concentration is 1×10~(17)cm-3 and the contact resistances under different alloying condition were examined by use of the probe stage. A transmission line model (TLM) was presented to calculate the contact resistivity and the optimum alloying condition of 450℃, 90s was chosen.On the basis of process study, power GaAs MESFETs with a output power over 500mW, a power gain no less than 7dB at 4GHz, and a Gate-Drain breakdown voltage of 30V were fabricated.
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