AlGaN/GaN肖特基结参数分析与电流运输机理研究

通过对AlGaN/GaN HEMT器件肖特基栅电流输运机理的研究,在变温下采用I-V法对AlGaN/GaN上的Ni/Au肖特基势垒高度和理想因子进行了计算. 通过对不同电流机理的分立研究,得到了更为准确的势垒高度值_b. 通过分析温度在300—550K之间肖特基反向泄漏电流的特性,得出结论：AlGaN材料的表面漏电不是HEMT器件反向泄漏电流的主要来源. 关键词： AlGaN/GaN异质结 肖特基结 理想因子     

基于I-V-T和C-V-T的GaN上Ni/Au肖特基接触特性研究

基于对制作在n-GaN上的肖特基二极管的变温I-V测试和C-V测试，采用表面势垒减薄模型对肖特基二极管的电流输运特性进行了研究.试验结果表明，肖特基接触的电流输运机理非常复杂，在不同的温度条件和偏压条件下有着不同的电流输运机理.在此基础上对肖特基接触I-V特性方程进行了修正，得到了很好的拟合曲线.试验表明，高温I-V法提取的势垒高度与常温C-V法提取的势垒高度接近于根据金属功函数得出的理论势垒高度值. 关键词： 氮化镓 肖特基二极管 表面势垒减薄模型 热电子场发射     

AlGaN/GaN高电子迁移率晶体管肖特基高温退火机理研究

在不同应力条件下,研究了AlGaN/GaN高电子迁移率晶体管高温退火前后的电流崩塌、栅泄漏电流以及击穿电压的变化.结果表明,AlGaN/GaN高电子迁移率晶体管通过肖特基高温退火以后,器件的特性得到很大的改善.利用电镜扫描(SEM)和X射线光电子能谱(XPS)对高温退火前、后的肖特基接触界面进行深入分析,发现器件经过高温退火后,Ni和AlGaN层之间介质的去除,并且AlGaN材料表面附近的陷阱减少,使得肖特基有效势垒提高,从而提高器件的电学特性. 关键词： AlGaN/GaN高电子迁移率晶体管 肖特基接触 界面陷阱     

组合材料方法研究膜厚对Ni/SiC电极接触性质的影响

采用组合材料方法研究了金属Ni膜厚对Ni/SiC接触性质的影响.16个膜厚均为18 nm的Ni/SiC电极具有较为一致的肖特基接触性质;膜厚从10 nm增加到160 nm,肖特基接触的电流-电压（I-V）曲线随膜厚发生显著变化.分析表明这种变化源于膜厚对理想因子n和有效势垒高度Ф_B的影响.1000℃快速退火后,这些肖特基接触都转变为欧姆接触,Ni₂Si是主要的生成物.I-V曲线测 关键词： 碳化硅 肖特基接触 欧姆接触 组合材料方法     

具有阻挡层的H等离子体处理增强型p-GaN栅AlGaN/GaN HEMT研究

采用H等离子体处理p-GaN盖帽层来制备p-GaN栅AlGaN/GaN高电子迁移率晶体管(HEMT).在p-Ga N层表面上先沉积2 nm的Al₂O₃薄膜,以减少H等离子体注入p-GaN时对表面造成的损伤.经研究表明沉积Al₂O₃阻挡层的器件栅极反向泄漏电流降低了一个数量级,开关比提高了约3倍.由于栅极泄露电流的减小,关态击穿电压从410 V提高到780 V.针对栅极反向泄漏减小的现象,进行了变温IG-VG测试,验证了栅极反向泄漏电流的主导机制是二维变程跳跃(Two-dimensional variable range hopping,2D-VRH)模型.分析了减小栅极反向电流的原因是由于Al₂O₃阻挡层改变了HR-Ga N的表面态,使陷阱能级的活化能升高.此外,器件动态特性也表现出更稳定的趋势,这是Al₂O₃薄膜阻挡过多的H等离子体的注入,使AlGaN势垒和沟道陷阱态数量减少,电流崩塌效应减弱.     

氮化硅介质中双层纳米硅薄膜的两级电荷存储

研究镶嵌在超薄非晶氮化硅(a-SiN_x)层之间的双层纳米硅(nc-Si)的电荷存储现象.利用等离子体增强化学气相淀积(PECVD)技术在硅衬底上制备a-SiN_x/a-Si/a-SiN_x/a-Si/a-SiN_x多层薄膜结构.采用常规热退火方法使非晶硅(a-Si)层晶化，形成包含双层nc-Si的金属-氮化物-半导体(MIS)结构.通过电容电压(C-V)特性测量，观测到该结构中由于电荷存储引起的C-V回滞现象，并在室温下成功观察到载流子基于Fowler-Nordheim(F-N)隧穿注入到第一层、第二层nc-Si的两级电荷存储状态.结合电流电压(I-V)特性的测量，对电荷存储的机理进行了深入分析. 关键词： 纳米硅 氮化硅 电容电压法 电流电压法     

牺牲Ni退火对硅衬底GaN基发光二极管p型接触影响的研究

本文通过在硅衬底发光二极管(LED)薄膜p-GaN表面蒸发不同厚度的Ni覆盖层,将其在N₂ ∶O₂=4 ∶1的气氛中、400℃—750℃的温度范围内进行退火,在去掉薄膜表面Ni覆盖层之后制备Pt/p-GaN欧姆接触层.实验结果表明:退火温度和Ni覆盖层厚度均对硅衬底GaN基LED薄膜p型欧姆接触有重要影响,Ni覆盖退火能够显著降低p型层中Mg受主的激活温度.经牺牲Ni退火后,p型比接触电阻率随退火温度的升高呈先变小后变大的规律,随Ni覆盖层厚度的增加呈先变小后变 关键词： 氮化镓 发光二极管 牺牲Ni退火 p型接触     

硼掺杂对四面体非晶碳膜电导性能的影响

以单质硼和高纯石墨的混合粉末压制成型的靶材作为靶源,采用过滤阴极真空电弧技术制备不同硼含量的掺硼四面体非晶碳膜.分别采用四探针法、阻抗分析仪和电化学界面对薄膜的变温电导率、I-V特性和C-V特性进行了测试和研究.实验结果表明,当B含量由0增加至6.04 at%时,薄膜的室温电导率先逐渐增大而后逐渐减小,相应薄膜的电导激活能先逐渐减小而后逐渐增大,并在2.13 at%时分别出现最大和最小值1.42×10^-7S/cm和0.1eV.此外,掺硼四面体非晶碳/n型硅异质结的I-V曲线表现出典型的整流特性,表明p-n结二极管已经形成,且结两端的掺杂能级在空间上连续统一. 关键词： 四面体非晶碳 电导率 I-V曲线')" href="#">I-V曲线 C-V曲线')" href="#">C-V曲线     

氢氟酸刻蚀对Ni/6H-SiC接触性质的作用

采用浓度为10%的氢氟酸（HF）刻蚀6H-SiC单晶片,研究了HF刻蚀时间对Ni/6H-SiC接触性质的影响．经24?h刻蚀的SiC基片在溅射Ni层后,其接触表现良好线性的电流-电压（I-V）曲线．低于这个腐蚀时间的接触具有明显的势垒,但在大于1000℃快速退火后,也得到了良好线性的I-V曲线．X射线衍射（XRD）和俄歇能谱（AES）深度元素分析表明Ni₂Si和C是快速退火后的主要产物．XRD和低能反射电子能量损失谱表明表层的C 关键词： 欧姆接触 SiC 富碳层 互扩散     

增强型AlGaN/GaN高电子迁移率晶体管高温退火研究

深入研究了两种增强型AlGaN/GaN高电子迁移率晶体管(HEMT)高温退火前后的直流特性变化.槽栅增强型AlGaN/GaN HEMT在500 ℃ N₂中退火5 min后,阈值电压由0.12 V正向移动到0.57 V,器件Schottky反向栅漏电流减小一个数量级.F注入增强型AlGaN/GaN HEMT在 400 ℃ N₂中退火2 min后,器件阈值电压由0.23 V负向移动到-0.69 V,栅泄漏电流明显增大.槽栅增强型器件退火过程中Schottky有效势垒     

Performance comparison of Pt/Au and Ni/Au Schottky contacts on AlxGa1-x N/GaN heterostructures at high temperatures

In contrast with Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts,this paper systematically investigates the effect of thermal annealing of Au/Pt/Al 0.25 Ga 0.75 N/GaN structures on electrical properties of the two-dimensional electron gas in Al 0.25 Ga 0.75 N/GaN heterostructures by means of temperature-dependent Hall and temperature-dependent current-voltage measurements.The two-dimensional electron gas density of the samples with Pt cap layer increases after annealing in N 2 ambience at 600℃ while the annealing treatment has little effect on the two-dimensional electron gas mobility in comparison with the samples with Ni cap layer.The experimental results indicate that the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts reduce the reverse leakage current density at high annealing temperatures of 400-600℃.As a conclusion,the better thermal stability of the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts than the Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts at high temperatures can be attributed to the inertness of the interface between Pt and AlxGa1-xN.     

Thermal stability of tungsten and tungsten nitride Schottky contacts to AlGaN/GaN

Thin tungsten nitride (WNx) films were produced by reactive DC magnetron sputtering of tungsten in an Ar-N2 gas mixture. The films were used as Schottky contacts on AlGaN/GaN heterostructures. The Schottky behaviours of WNx contact was investigated under various annealing conditions by current-voltage (I-V ) measurements. The results show that the gate leakage current was reduced to 10-6 A/cm2 when the N2 flow is 400 mL/min. The results also show that the WNx contact improved the thermal stability of Schottky contacts. Finally, the current transport mechanism in WNx/AlGaN/GaN Schottky diodes has been investigated by means of I-V characterisation technique at various temperatures between 300 K and 523 K. A TE model with a Gaussian distribution of Schottky barrier heights (SBHs) is thought to be responsible for the electrical behaviour at temperatures lower than 523 K.     

Al2O3绝缘层的AlGaN/GaN MOSHEMT器件研究

在研制AlGaN/GaN HEMT器件的基础上,采用ALD法制备了Al₂O₃ AlGaN/GaN MOSHEMT器件.通过X射线光电子能谱测试表明在AlGaN/GaN异质结材料上成功淀积了Al₂O₃薄膜.根据对HEMT和MOSHEMT器件肖特基电容、器件输出以及转移特性的测试进行分析发现：所制备的Al₂O₃薄膜与AlGaN外延层间界面态密度较小,因而MOSHEMT器件呈现出较 关键词： 2O₃')" href="#">Al₂O₃ ALD GaN MOSHEMT     

Influence of thermal stress on the characteristic parameters of AlGaN/GaN heterostructure Schottky contacts

Ni Schottky contacts on AlGaN/GaN heterostructures have been fabricated. The samples are then thermally treated in a furnace with N₂ ambient at 600 ^circC for different times (0.5, 4.5, 10.5, 18, 33, 48 and 72 h). Current-voltage (I-V) and capacitance-voltage (C-V) relationships are measured, and Schrödinger's and Poisson's equations are self-consistently solved to obtain the characteristic parameters related to AlGaN/GaN heterostructure Schottky contacts: the two-dimensional electron gas (2DEG) sheet density, the polarization sheet charge density, the 2DEG distribution in the triangle quantum well and the Schottky barrier height for each thermal stressing time. Most of the above parameters reduce with the increase of stressing time, only the parameter of the average distance of the 2DEG from the AlGaN/GaN interface increases with the increase of thermal stressing time. The changes of the characteristic parameters can be divided into two stages. In the first stage the strain in the AlGaN barrier layer is present. In this stage the characteristic parameters change rapidly compared with those in the second stage in which the AlGaN barrier layer is relaxed and no strain is present.     

C-V analysis of rapidly thermal annealed SF6 plasma treated AlGaN/GaN heterostructures

We studied influence of rapid thermal annealing on electrical parameters of SF₆ plasma treated AlGaN/GaN heterostructures. The main emphasis by the evaluation was laid on C-V measurement and simulation, but also I-V and SIMS measurement were used. It was found that the diminished sheet carrier concentration of a two-dimensional electron gas after plasma treatment recovered significantly at the temperature of 500 °C. By using C-V measurement, it was possible to assess besides the changes of the two-dimensional electron gas concentration after annealing also the changes in the Schottky barrier heights and to find out the doping concentration in AlGaN barrier and GaN channel layer. The trend in Schottky barrier height changes after annealing was confirmed also by I-V measurement.     

AlGaN/GaN异质结载流子面密度测量的比较与分析

对MOCVD技术在蓝宝石衬底上生长的不同Al组分AlGaN/GaN异质结进行了范德堡法Hall测量和电容-电压(C-V)测量，发现Hall测量载流子面密度值大于C-V测量值，并且随着AlGaN层Al组分的增加，两种测量值都在增加，同时它们的差值也在增加.认为产生这一结果的原因有两方面.一方面，Ni/Au肖特基金属淀积在AlGaN/GaN异质结上，改变了AlGaN势垒层的表面状态，使得一部分二维电子气(2DEG)电子被抽取到空的施主表面态中，从而减小了AlGaN/GaN异质结界面势阱中的2DEG浓度.随着势垒层Al组分的增加，AlGaN层产生了更多的表面态，从而使得更多的电子被抽取到了空的表面态中.另一方面，由于C-V测量本身精确度受到串联电阻的影响，使得测量电容小于实际电容，从而低估了载流子浓度.     

Influence of thermal stress on the relative permittivity of the AlGaN barrier layer in an AlGaN/GaN heterostructure Schottky contacts

Ni Schottky contacts on AlGaN/GaN heterostructures were fabricated. Some samples were thermally treated in a furnace with N₂ ambience at 600 °C for different times (0.5 h, 4.5 h, 10.5 h, 18 h, 33 h, 48 h, and 72 h), the others were thermally treated for 0.5 h at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C). With the measured current—voltage (I—V) and capacitance—voltage (C—V) curves and by self-consistently solving Schrodinger's and Poisson's equations, we found that the relative permittivity of the AlGaN barrier layer was related to the piezoelectric and the spontaneous polarization of the AlGaN barrier layer. The relative permittivity was in proportion to the strain of the AlGaN barrier layer. The relative permittivity and the strain reduced with the increased thermal stress time until the AlGaN barrier totally relaxed (after 18 h at 600 °C in the current study), and then the relative permittivity was almost a constant with the increased thermal stress time. When the sample was treated at 800 °C for 0.5 h, the relative permittivity was less than the constant due to the huge diffusion of the contact metal atoms. Considering the relation between the relative permittivity of the AlGaN barrier layer and the converse piezoelectric effect, the conclusion can be made that a moderate thermal stress can restrain the converse piezoelectric effect and can improve the stability of AlGaN/GaN heterostructure devices.     

Comparison of electrical characteristic between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated.Based on the measured current–voltage and capacitance–voltage curves,the electrical characteristics of AlN/GaN Schottky diode,such as Schottky barrier height,turn-on voltage,reverse breakdown voltage,ideal factor,and the current-transport mechanism,are analyzed and then compared with those of an AlGaN/GaN diode by self-consistently solving Schrdinger’s and Poisson’s equations.It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes.However,more dislocation defects and a thinner barrier layer for AlN/GaN heterostructure results in a larger tunneling probability,and causes a larger leakage current and lower reverse breakdown voltage,even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an AlGaN/GaN diode.