金属/氮化物肖特基势垒和欧姆接触研究进展

金属 /氮化物肖特基势垒和欧姆接触是蓝紫光光学器件及高温大功率电子器件中的关键工艺。氮化物半导体是一种极性材料 ,表面态密度较低 ,费米能级钉扎效应较弱 ,表面处理能显著影响接触特性。样品表面的沾污和氧化层也会使接触特性显著退化。宽禁带材料的杂质离化能高 ,重掺杂比较困难。深能级陷阱对载流子的俘获效应很强。这些因素都增加了接触的制作难度 ,促使人们寻求新的方案来改进接触特性。文中从金属 /半导体接触的物理模型出发来综述肖特基势垒和欧姆接触的研究进展 ,希望能给器件研究者提供新的思路。     

Characterization of Epitaxial Indium Nitride Interlayers for Ohmic Contacts to Silicon Carbide

Ohmic contacts to n-type 4H- and 6H-SiC without postdeposition annealing were achieved using an interlayer of epitaxial InN beneath a layer of Ti. The InN films were grown by reactive dc magnetron sputtering at 450°C, whereas the Ti films were deposited by electron-beam evaporation at room temperature. The InN films were characterized by x-ray diffraction (XRD), secondary electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM), and Hall-effect measurements. Both XRD and TEM observations revealed that the Ti and InN films have epitaxial relationships with the 6H-SiC substrate as follows: (0001)[]_Ti∥(0001)[]_InN∥(0001)[]_6H-SiC. The Ti/InN/SiC contacts displayed ohmic behavior, whereas Ti/SiC contacts (without an InN interlayer) were nonohmic. These results suggest that InN reduces the Schottky barrier height at the SiC surface via a small conduction-band offset and support previous reports of an electron accumulation layer at the surface of InN.     

Low Resistance Contacts to p-CulnSe2 and p-CdTe Crystals

Room temperature formation of ohmic contacts by electroplating gold on chemically treated surfaces of p-CuInSe₂ and p-CdTe single crystals is reported. The effect of Br₂/methanol and KOH+KCN+H₂O treatments prior to plating was analyzed in the case of CuInSe₂. It is shown that the former treatment yields better ohmic contacts, with lower contact resistance, than the latter. While annealing these contacts made them highly non-ohmic, the method gives reasonably ohmic contacts on surfaces, that were purposely oxidized prior to contact preparation. In the case of p-CdTe stable, low resistance ohmic contacts were obtained at room temperature by electrochemical diffusion of Hg from solution, prior to gold plating. The treatment forms a highly degenerated p^+- HgCdTe layer. The contacts, which have a very low contact to bulk resistivity ratio, were further improved by vacuum annealing.     

A Novel Stress Characterization Technique for the Development of Low-Stress Ohmic Contacts to HgCdTe

HgCdTe material intended for long-wavelength infrared detection is particularly susceptible to damage from stress. As a result, an ideal ohmic contact needs to have good adhesion and low specific contact resistance. The contact should act as a diffusion barrier and induce the least amount of stress in the underlying material. In this paper we present a set of stress measurements from different ohmic contact materials deposited on short- and long-wavelength HgCdTe films grown by liquid-phase epitaxy (LPE). Using a new experimental technique we remove the substrate and measure the stress induced on single- and multilayered HgCdTe cantilevers. To interpret our results, we develop a theoretical model that describes the physics of elastic deformation in HgCdTe layers. Our model is based on classical thin-plate bending theory and explicitly takes into account the realistic boundary conditions that are present in the experimental setup by using a variational approach.     

Long-term thermal stability of Ti/Al/Mo/Au ohmic contacts on n-GaN

Improved performance of the ohmic contacts on n-GaN has been demonstrated with the use of MoAu as the capping layer on TiAl metallization. Contact resistance as low as 0.13 Θ-mm was achieved in these ohmic contacts when annealed at 850°C for 30 sec. We have studied the long-term thermal stability of these contacts at 500°C, 600°C, 750°C, and 850°C, respectively. The Ti/Al/Mo/Au metallization forms low contact-resistance ohmic contacts on n-GaN that are stable at 500°C and 600°C after 25 h of thermal treatment. The ohmic-contact performance degrades after 10 h of thermal treatment at 750°C, while the contacts exhibit nonlinear current-voltage (I-V) characteristics after 1 h of thermal treatment at 850°C with the formation of oxide on the surface of the contacts accompanied by surface discoloration. The intermetallic reactions taking place in the contacts during the long-term thermal treatments were studied using Auger electron spectroscopy (AES), and the surface morphology was characterized using atomic force microscopy (AFM).     

硫铵滚筒干燥器自动测控系统的应用研究

简述了硫铵滚筒干燥器的干燥原理及工艺流程,提出自动测控系统的控制要求及实现方案配置,给出了硫铵含水量控制调节、干燥器出口微负压控制调节、水溶雾沫除尘器等几个关键环节的测控原理及控制过程。     

含硅过共析钢晶界铁素体形成的热力学分析

将合金元素在珠光体相变时无分配状态下形成的含Ｓｉ合金渗碳体做为一种介稳相处理，利用规则溶液亚点阵模型和有关文献中的数据，计算了含Ｓｉ合金渗碳体相对于无Ｓｉ渗碳体的自由能增量δＧＦｅ３ＣＳｉ，得到了渗碳体中含Ｓｉ量和δＧＦｅ３ＣＳｉ的对应关系；并利用Ｓｉ在不同温度下的分配系数，计算了Ｓｉ对ＦｅＣ合金介稳态γ／［γ＋Ｆｅ３Ｃ］相界碳浓度（Ａ′ｃｍ）的影响。所得结果认为，含Ｓｉ过共析钢珠光体转变时在原奥氏体晶界出现连续网状铁素体，是Ｓｉ增加含Ｓｉ渗碳体自由能，从而提高了介稳态γ／［γ＋Ｆｅ３Ｃ］相界碳浓度（Ａ′ｃｍ）的结果。     

镍、铜低合金奥贝球铁特性研究

阐明了含Ni、Cu质量分数分别为1.5%和0.8%的奥贝球铁的凝固/相变和性能特点。测定了凝固过程的微分热分析曲线、膨胀仪曲线、绘制了奥氏体连续冷却较变曲线和等温转变动力学曲线,对比分析了该成分铸铁的淬透性。测定了Ni、Cu合金化奥贝球铁的常温力学性能。