Au与p-CZT晶体的接触特性及其CZT表面处理状态的影响

对不同腐蚀、钝化表面处理的CZT晶片与Au接触的I-V特性进行了研究.用XPS分析了钝化前后CZT晶体表面成分,发现钝化后CZT晶片表面形成厚度为3.1nm的TeO2氧化层.用Agilent 4339B高阻仪进行未腐蚀、腐蚀与腐蚀钝化的CZT晶片I-V特性测试,结果表明腐蚀和腐蚀钝化均能不同程度提高Au/p-CZT接触的势垒高度,相应地减小了漏电流.     

Hg1-xMnxTe晶片电学参数的测量及分析

采用范德堡法分别在77K和室温下对多个Hg1-xMnxTe晶片的电学性能进行了测量,发现部分晶片在77K下的导电类型为p型,而在室温下却为n型.通过理论分析对此现象进行了解释.分析表明:Hg1-xMnxTe晶片中电子迁移率与空穴迁移率的比值较大和Hg1-xMnxTe的禁带较窄是造成晶片导电类型转变的主要原因.对所测其它电学参数的理论分析表明范德堡法不适合用于Hg1-xMnxTe晶片室温时的载流子浓度和迁移率的测量,但仍可用其对晶片室温时的电阻率和霍尔系数进行测量.     

rGO-AuNPs/n-Si的肖特基接触特性研究

通过水热法制备了还原氧化石墨烯负载Au纳米复合材料(rGO-AuNPs),结合旋涂法,将其涂覆在单晶硅表面,制备出rGO-AuNPs/n-Si肖特基接触。结果表明,rGO-AuNPs的衍射峰以单质Au为主,存在较弱的石墨烯衍射峰,同时纳米Au粒子(Au nanoparticles, AuNPs)较均匀分布在石墨烯表面,表明成功合成了负载Au的还原氧化石墨烯。从电流-电压(Current-voltage,I-V)曲线可以看出rGO-AuNPs/n-Si肖特基接触具有整流特性。在负载量下,随着Au含量的递增,肖特基势垒高度增加,理想因子减小,但漏电流增大,可能是由于氧化石墨烯在还原过程中缺陷的存在,产生了隧道电流和镜像力,降低了肖特基势垒的横向均匀性。     

Ti/Al/Ni/Au与n型GaN的欧姆接触研究

通过电流 电压 (I V)特性和传输线方法 (TLM )测量研究在n型GaN上淀积Ti/Al/Ni/Au电极形成欧姆接触的机制。Ni/Au作为Ti/Al的覆盖层起了阻止Ti ,Al,Au的互扩散及抗接触层氧化的作用。在 4 0 0℃到 90 0℃范围内 ,Ti/Al/Ni/Au与n型GaN的接触电阻随温度升高先略有上升 ,到 5 0 0℃以后单调下降。而表面形貌却在合金温度高于6 0 0℃以后随温度升高逐步变差。通过两步合金法得到了n GaN上Ti/Al/Ni/Au形成的接触电阻低达 9.6 5× 1 0 - 7Ωcm2 。最后还对两步合金法形成n GaN欧姆接触的机制进行了讨论。     

ZnO上肖特基接触的研究进展

由于ZnO存在本征施主缺陷(锌间隙和氧空位),使得表面存在较高浓度的施主能级,难以获得肖特基接触.本文回顾了近年来在n型ZnO上制备肖特基接触的研究进展,对n型ZnO上制备肖特基接触的Au、Pt、Pd、Ag等金属方案的性能与特点,以及影响接触性能等因素,如表面处理和退火等进行了分析与归纳.同时,对P型ZnO上难以获得肖特基接触的原因进行了讨论.另外,由于Au、Pt等金属普遍存在热稳定差的问题,会降低ZnO基大功率器件的寿命,寻找能与n型ZnO能形成高热稳定性、低泄露电流、高势垒高度的肖特基接触材料是未来ZnO上肖特基光电器件的发展方向.     

CdZnTe晶片表面钝化研究

用NH4F／H2O2对Br2-MeOH抛光CdZnTe晶片表面进行了表面钝化处理,通过I-V测试及XPS分析分别对钝化前后的CZT晶片的电学性能和表面组成进行了表征。I-V测试结果表明NH4F／H2O2对CdZnTe晶片表面有较好的钝化效果,电流下降率随所加偏压的增加而下降。在10V偏压下,电流下降最明显,下降率为73．7％。与欧姆定律发生偏离的临界场强为333V／cm。XPS分析发现,用NH4F／H2O2处理可使CdZnTe表面富集的Te79.28％被氧化成TeO2,氧化层的厚度约为3．15nm。钝化后的表面更接近CdZnTe的化学计量配比。     

Bi2O3薄膜的制备及其电阻开关特性的研究

电阻式存储器由于具有众多的优点有望成为最有前景的下一代高速非挥发性存储器的选择之一.实验利用射频磁控溅射法在重掺硅上沉积了Bi2O3薄膜,并对该薄膜的结晶状态和Au/Bi2O3/n+Si/Al结构的电阻开关特性进行了研究.XRD分析结果表明,射频磁控溅射法沉积所得的Bi2O3薄膜结晶性能好,(201)取向明显.I-V曲线测试结果表明,Au/Bi2O3/n+Si/Al结构具有单极性电阻开关特性.通过对不同厚度Bi2O3薄膜的Au/Bi2O3/n+Si/Al结构I-V特性比较发现,随着薄膜厚度的增加,电阻开关的Forming、Set和Reset阈值电压均随之增加.对于Bi2O3薄膜厚度为31.2 nm的Au/Bi2O3/n+Si/Al结构,其Forming、Set和Reset阈值电压均低于4 V,符合存储器低电压工作的要求.     

Ni/Au、Pd/Au与p-AlGaN材料的接触特性

在AlGaNpin型日盲紫外探测器结构中的p-AlGaN层上生长了Ni/Au和Pd/Au,并在600～850℃温度下进行快速热退火,测量其退火前后传输线模型中各金属接触间的电学性质。实验发现,Ni/Au与Pd/Au在p-AlGaN上表现出了不同的接触性能。为了更好的说明金属与p-AlGaN材料接触之间在退火后电流的变化,还测量了p-AlGaN材料裸片两点之间I-V曲线在退火前后的变化。实验表明,比起Ni/Au来,Pd/Au在p-AlGaN材料上制备欧姆接触具有一定的优势,并在文中进行了分析。     

Cu/Ag导电薄膜与高阻CdZnTe的接触性能研究

采用射频磁控溅射法在高阻Cd0.9Zn0.1Te上制备了Cu/Ag导电薄膜,通过测量I-V曲线来评价接触性能。讨论了溅射功率和衬底温度对接触性能的影响,结果表明在两种不同功率下制备的薄膜不经过热处理已具有良好的欧姆接触性能,随着衬底温度的升高欧姆接触性能有所下降。通过对衬底的表面处理降低了表面漏电流。对试样进行退火处理使接触性能有所改善,退火温度在300℃时的接触性能要好于420℃。利用红外透过率来验证了退火温度范围及所选择加热衬底温度对高阻Cd0.9Zn0.1Te衬底没有影响。     

不同沉积工艺下Au/P-CdZnTe接触界面的研究

采用超声波扫描(SAM)、俄歇电子能谱分析技术(AES)、电极粘附力测试和I-V特性测试等方法研究了化学沉积、溅射和真空蒸发三种不同沉积工艺条件下Au/p-CdZnTe接触界面的各种特性.通过实验结果可以看出,化学法沉积的Au电极能形成较好的欧姆接触特性,但其操作工艺不容易控制,电极接触层均匀性较差,在器件使用过程中,容易引起电极的退化;溅射沉积的Au电极有着较好的附着力,但对CdZnTe表面的损伤较大,欧姆接触特性较差;真空蒸发法沉积的Au电极,有着较好的欧姆接触特性,且其电极接触层也较为均匀,只是电极附着力相对较小,但可以通过合适的退火工艺进行改善.     

Thermal stability of N-polar n-type Ohmic contact for GaN-based light emitting diode on Si substrate

Thermal stability of N-polar n-type Ohmic contact for GaN light emitting diode (LED) on Si substrate was investigated. Al/Ti/Au were deposited as the contacts on the N-polar n-type GaN with and without AlN buffer layer on the surface, respectively, and both contacts exhibited Ohmic behaviors. The samples with AlN showed excellent Ohmic contact thermal stability when annealed below 700 °C, while the samples without AlN experienced serious degradation on electrical properties after being annealed in the temperature range of 250-600 °C. After the process of aging at 30 mA (155 A/cm²) and room temperature for 1000 h, operating voltage increase less than 0.05 V for LEDs with AlN but more than 0.45 V for LEDs without AlN. Therefore, we conclude that the existence of AlN buffer layer is a key of forming high stable Ohmic contact for GaN-based vertical structure LED on Si substrate.     

Microstructure evolution and development of annealed Ni/Au contacts to GaN nanowires

The development of Ni/Au contacts to Mg-doped GaN nanowires (NWs) is examined. Unlike Ni/Au contacts to planar GaN, current-voltage (I-V) measurements of Mg-doped nanowire devices frequently exhibit a strong degradation after annealing in N(2)/O(2). This degradation originates from the poor wetting behavior of Ni and Au on SiO(2) and the excessive void formation that occurs at the metal/NW and metal/oxide interfaces. The void formation can cause cracking and delamination of the metal film as well as reduce the contact area at the metal/NW interface, which increases the resistance. The morphology and composition of the annealed Ni/Au contacts on SiO(2) and the p-GaN films were investigated by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) measurements. Adhesion experiments were performed in order to determine the degree of adhesion of the Ni/Au films to the SiO(2) as well as observe and analyze the morphology of the film's underside by SEM. Device degradation from annealing was prevented through the use of a specific adhesion layer of Ti/Al/Ni deposited prior to the nanowire dispersal and Ni/Au deposition. I-V measurements of NW devices fabricated using this adhesion layer showed a decrease in resistance after annealing, whereas all others showed an increase in resistance. Transmission electron microscopy (TEM) on a cross-section of a NW with Ni/Au contacts and a Ti/Al/Ni adhesion layer showed a lack of void formation at the contact/NW interface. Results of the XRD and TEM analysis of the NW contact structure using a Ti/Al/Ni adhesion layer suggests Al alloying of the Ni/Au contact increases the adhesion and stability of the metal film as well as prevents excessive void formation at the contact/NW interface.     

ZnO上欧姆接触的研究进展

为制备高性能的ZnO基器件如UV光发射器，探测器、场效应晶体管，在ZnO上形成优良的金属电极是十分必要的。回顾了近年来ZnO上制备欧姆接触的新进展，对在n型ZnO上制备欧姆接触的Al，A1/Pt，A1/Au，Ti/Al，Ti，AU，Ti/A1/Pt/Au，Re/Ti/Au等金属化方案的性能与特点，以及影响欧姆接触电阻率和热稳定性的因素，如表面处理和退火等进行了分析与归纳。同时，对P型ZnO上难以获得低接触电阻的原因进行了讨论。文章还简要说明了ZnO上透明欧姆接触的研究现状，指出获得低阻、高导电、高透光和高热稳定性的接触是未来ZnO基光电器件的发展方向。     

The influence of external bias voltage on electrical properties of YBa2Cu3O7−x /metal point contact interface

We have investigated a change of electrical properties of YBa₂Cu₃O₇−δ/metal point contact immediately after its preparation depending on time, temperature as well as external bias voltage. The increase of the point contact differential resistance in time was experimentally observed at temperature above 200 K even if no external bias voltage was applied. The low external bias voltage considerably influences the time increase of the differential resistance indicating an important role of oxygen diffusion. It is shown on differential characteristics that for Au, In the parameters of tunneling barrier such as the average height and width are constant in time whereas for Al, Pb an evolution of the tunneling barrier was observed because of oxidation of Al and Pb. Applying of higher bias voltage (up to 1 V) enables the transport of oxygen even below 200 K (down to 4.2 K) and changes the electrical properties of YBCO/metal point contact interface. The differential characteristics change their behaviour from that typical for NIS contact with strong tunneling barrier to NS contact with a high transparency of the interface. All the above changes are reversible upon changing the bias voltage polarity.     

Schottky diode fabricated on a single crystalline diamond rod

The fabrication process of Al/diamond Schottky diodes on single crystalline diamond rods (SCDRs) was demonstrated. SCDRs of submicron diameters were obtained by etching a polished polycrystalline diamond film in oxygen plasma. The as-scratched SCDR was confirmed to be single crystalline diamond by electron diffraction measurements showing the same fuzzy spot pattern at different parts of an SCDR. Each SCDR was extracted from a grain in the polycrystalline film where the grain size served as a limit of the length of an SCDR. Al/Ti and Al metals were deposited to form ohmic and Schottky contacts, respectively. A hydrogen plasma treatment is an essential step prior to the formation of an Al/diamond Schottky contact in order to improve the device performance. The submicron scale Al/diamond Schottky diode exhibits a very high current density of 1.4 × 10(4) A cm(-2) at a forward bias (V(F)) voltage of - 3 V.     

Metal contacts to n-type AlGaAs grown by molecular beam epitaxy

We report for the first time the barrier heights of Cu, Ni, Ag, Ti on etched n-type Al_0.33Ga_0.67As and their dependence on annealing temperature with I–V and C–V techniques. The barrier heights of Al and Au, measured for comparison, are 0.96 and 1.06 eV, respectively, in excellent agreement with the results reported previously. The barrier heights of the Cu, Ni, Ag and Ti/n---Al_0.33Ga_0.67As diodes are found to be 1.08, 0.90, 0.87 and 0.87 eV, respectively. It is observed that the barrier heights for Al, Au, Cu and Ti contacts monotonically decrease with annealing temperature. For the Ag and Ni contacts, however, they become higher after being annealed at 473 K for 10 min and become lower thereafter, accompanied by a change of their ideality factors in opposite direction. The barrier heights extrapolated from C–V measurements for all metals studied are higher than that deduced from I–V data, and become higher after annealing at high temperatures, indicating the existence of a thin oxide layer at interface and broadening of the oxide after annealing. Our results can be qualitatively explained by the quality of contact and defects created at the semiconductor surface due to interdiffusion.     

Current rectification in a single silicon nanowire p-n junction

Diodes within individual silicon nanowires were fabricated by doping them during growth to produce p-n junctions. Electron beam lithography was then employed to contact p- and n-doped ends of these nanowires. The current-voltage (I-V) measurements showed diode-like characteristics with a typical threshold voltage (Vt) of about 1 V and an ideality factor (n) of about 3.6 in the quasi-neutral region. The reverse bias I-V measurement showed an exponential behavior, indicating tunneling as the current leakage mechanism.     

Improved Al/Si ohmic contacts to p-type 4H-SiC

An AlSi-based ohmic contact with a new composition is reported in this paper. AlSi(2%)Ti(0.15%) contacts are formed by evaporation on p-type 4H-SiC grown by liquid phase epitaxy (LPE) and annealed in the temperature range from 700 to 950°C. The ohmic behaviour has been checked by I–V characteristics and the contact resistivity has been measured by the linear transmission-line-model (TLM) method. The dependence of the contact resistivity on the annealing conditions has been studied. An ohmic behaviour has been established at 700°C while the lowest contact resistivity value of 9.6×10⁻⁵ Ω cm² has been obtained after annealing at 950°C. The thermal stability of both Al/Si/SiC and AlSiTi/SiC contacts at a temperature of 600°C has been studied. It has been found that the AlSiTi/SiC contacts are stable for 100 h at this ageing temperature while the Al/Si/SiC contacts deteriorate after 24 h.