In0.53Ga0.47As PIN光电探测器的温度特性分析

从理论和实验上分析了双异质结In0.53Ga0.47As PIN光电探测器在不同的反向偏置电压下暗电流在甚宽温度范围内的温度特性。结果表明：在反向偏置低压与高压段,产生一复合电流与隧道电流(缺陷隧道电流与带带间隧道电流)分别占主导地位,并呈现出相应的温度特性。还从理论与实验两方面探讨了噪声对探测器R0A的影响,结果表明：在低温段,产生一复合噪声起主要作用,在高温段,俄歇复合噪声起主要作用。     

高性能In0.53Ga0.47AsPIN光电探测器的研制

报道了采用GSMBE方法研制的In0.53Ga0.47As PIN光电探测器，器件结构中引入了宽禁带InP窗口层和聚酰亚胺钝化工艺，减小了暗电流，提高了器件性能。在反向偏压为5V时器件的暗电流为640pA，反向偏压为10V时测得器件的上升时间为37.2ps，下降时间为30.45ps，半高宽为43.9ps。对影响探测器暗电流的因素和提高响应速度的途径进行了讨论。     

氮化镓肖特基结紫外探测器的异常特性测量

测量了CaN肖特基结紫外探测器在有、无光照下的I-V异常特性。分别用362nm和368nm光束对有源区进行横向扫描,得到了光照不同部位时探测器在无偏压、2V反向偏压下的电流。紫外光照到肖特基结压焊电极附近及透明电极边沿附近区域时,探测器在反向偏压下有较大增益,空间响应均匀性变差,在禁带内有两个增益响应峰波长——364nm和368nm。探测器在810nm光照射下,反向偏压下的光响应增益、持续光电导存在光淬灭现象。探测器紫外光照完后,俘获中心及表面陷阱所俘获的部分电荷在高反向偏置电压下老化可以通过隧穿或发射效应释放出来,经过高反向偏置电压老化完后的探测器在同一低反向偏置电压下暗电流比老化前的要小。测量结果为GaN器件的研制提供了参考数据。     

InGaAs红外探测器的γ辐照研究

研究了γ射线辐照对InGaAs红外探测器性能的影响。γ射线的辐照剂量分别为10Mrad、20Mrad、30Mrad。测量了器件在不同γ辐照剂量下的响应光谱、电流一电压特性、信号、噪声。通过对实验结果的分析,发现器件的响应光谱和信号没有发生明显变化;暗电流和噪声随γ辐照剂量增加而递增,表明探测器的性能随γ辐照剂量的增加而逐步衰减。     

镍硅颗粒膜的表面传导电子发射特性

本文提出采用镍硅颗粒薄膜作为表面传导电子发射显示的发射体材料,通过光刻和磁控溅射在两电极(10μm间隙)之间制备30 nm厚的镍硅颗粒膜。施加三角波电压进行电形成工艺,并测试了器件的电学特性。获得主要结果有,在器件阳极电压2000 V和器件阴极电压13 V的作用下,可以重复探测到稳定的器件发射电流,并且随器件阴极电压的增加而明显增加,最大的发射电流达到了1.84μA(共18个单元);电形成过程中,单个发射体单元的薄膜电阻从13Ω增加到10913Ω;通过对器件发射电流的Fowler-Nordheim结分析,可以确定电子发射机理属于场致电子发射。     

高温Ti/4H-SiC肖特基势垒二极管的特性

在研究高温下串联电阻Ron对肖特基势垒二极管正向特性的影响，以及各种反向电流密度分量对其反向特性的影响基础上，测量并理论计算了300－528K范围内Ti/4H-SiC肖特基势垒二极管的伏安特性。分别得到了理想因子、肖特基势垒高度和串联电阻在395K和528K温度下的数值。理论和实验的比较说明，高温下，热电子发射是正向电流的主要输运机理，反向电流除了以隧道效应为主外，热电子发射电流和耗尽层中复合中心产生电流都随温度的升高而大大增加，必须加以考虑。     

InAlAs／InGaAs MSM光电探测器

采用ＧＳＭＢＥ方法及典型的器件工艺制成了用ＩｎＡｌＡｓ作为肖特基势垒增强材料的高性能ＩｎＡｌＡｓ／ＩｎＧａＡｓ／ＩｎＰ ＭＳＭ光电探测器。用自制的测试系统对器件的直流和瞬态特性进行了测试，测试结果表明，器件的击穿电压大于３０Ｖ，在１０Ｖ偏压下暗电流小于２０ｎＡ，对应的暗电流密度为３ｐａ／μｍ＾２，优于已有文献的报导。     

钢球表面缺陷检测用双光路光源稳定控制技术研究

半导体激光器作为光源产生器件进行钢球表面缺陷检测时，由于其自身的材质和结构，输出光功率受注入电流和温度变化的影响很大，光源很容易产生波动，这对检测结果产生了较大的干扰，影响钢球表面缺陷检测的准确率。本文设计了一种用于钢球表面质量检测的小功率半导体激光器功率稳定系统。通过上位机对单片机烧录程序实现对半导体激光器发光功率的自动控制，系统设计有光功率反馈模块、温度控制模块和光隔离模块，可以有效的消除电流浪涌现象、温度变化和反射光干扰等因素对激光器输出功率的影响，保证激光器发出恒定功率的稳定光。最后对1310 nm的激光器进行了测试，该系统将光功率的不稳定度从9.37%降低到1.42%，为后续的钢球表面缺陷检测奠定了良好的基础。     

溶胶-凝胶法制备MgxZn1-xO薄膜及性能研究

采用溶胶-凝胶法在石英玻璃片衬底上制备了Mg2+掺杂的ZnO(MgxZn1-xO)薄膜,研究了Mg2+掺杂对ZnO薄膜结构和紫外透过率的影响;在氧化物薄膜上真空蒸镀了Al叉指电极,制得紫外原型探测器件,测试了I-Ⅴ特性.结果表明,Mg2+掺杂后,MgxZn1-xO薄膜为纤锌矿结构,随着x值增加,晶格常数c逐渐减少,α逐渐增大,Mg2+掺杂抑制了(002)晶面的生长;紫外透过光谱表明,Mg2+掺杂后吸收边发生蓝移,可提高ZnO薄膜的禁带宽度;I-Ⅴ特性曲线表明,正向偏压下探测器的暗电流和光照电流随外加偏压呈线性增长,但光照电流与暗电流的差别较大.     

氧气等离子体处理对AlGaN肖特基接触的影响

研究了不同的干法刻蚀以及氧气等离子体处理条件对AlGaN表面特性的影响。在合适的条件下,氧气等离子体处理可以使AlGaN表面发生氧化,并使肖特基接触的反向漏电流降低两个数量级,反向击穿电压也有显著提高。该方法简单易行,可应用于制备高性能的AlGaN／GaN HEMT器件。     

High current density Esaki tunnel diodes based on GaSb-InAsSb heterostructure nanowires

We present electrical characterization of broken gap GaSb-InAsSb nanowire heterojunctions. Esaki diode characteristics with maximum reverse current of 1750 kA/cm(2) at 0.50 V, maximum peak current of 67 kA/cm(2) at 0.11 V, and peak-to-valley ratio (PVR) of 2.1 are obtained at room temperature. The reverse current density is comparable to that of state-of-the-art tunnel diodes based on heavily doped p-n junctions. However, the GaSb-InAsSb diodes investigated in this work do not rely on heavy doping, which permits studies of transport mechanisms in simple transistor structures processed with high-κ gate dielectrics and top-gates. Such processing results in devices with improved PVR (3.5) and stability of the electrical properties.     

High-voltage GaAs diodes with subnanosecond gate voltage recovery

High-voltage GaAs switching diodes with subnanosecond characteristic times of reverse current decay on switching from forward to reverse bias were studied. The diode structures studied had impurity concentration profiles in the base region close to those of the charge-storage diodes and operated in the regimes corresponding to those employed in silicon-based high-voltage fast-recovery drift diodes. The application prospects of the proposed GaAs diodes are demonstrated, for example, in the devices generating pulses with a front width of several hundred picoseconds, a current of several hundred amperes, and a voltage of a several kiloelectronvolts at a frequency of up to several hundred kilohertz.     

A novel biasing scheme for I-MOS (impact-ionization MOS) devices

A novel biasing scheme for impact-ionization metal-oxide semiconductor (I-MOS) devices was proposed based on the physics of the device, which features negative biasing at the source region. To confirm the proposed idea, we have simulated an I-MOS whose gate length is 130 nm. According to the simulation results, by increasing the value of the reverse source-to-body bias, we can enhance the electrical characteristics of I-MOS devices. With the source bias of -6.5 V, a 130-nm I-MOS has a threshold voltage of 0.19 V, a subthreshold swing of 3 mV/dec, and a drain induced current enhancement of 20 mV/V. The proposed biasing scheme will make the I-MOS more useful and lead it to act as an ideal switch.     

Diode-like properties of as-grown chemical vapor deposited single-walled carbon nanotubes

Current rectification property of as-grown single-walled carbon nanotubes (SWNTs) is investigated. The SWNTs are grown by chemical vapor deposition (CVD) process. The process allowed to grow long strands of SWNT bundles, which are then used to fabricate multiple arrays of switching devices with the channel length of 3, 5, 7 and 10 microm on a 15 mm x 15 mm SiO2 on Si substrate. Regardless of the channel length, a majority of the fabricated devices show current rectification characteristics, with high throughput of current (I) in the forward bias (V) giving the forward and reverse current ratio (Ifor/Irev) of approximately 10(6). Atomic force microscopic (AFM) analysis of the device structure and surface topology of SWNT suggest the observed rectification of current to possibly result from (a) cross-tube junctions, (b) a mixture of metallic and semiconducting tubes in the SWNT bundles, and/or (c) chirality change along a single tube. The exact mechanism underlying the observed rectification could not be conclusively established. However, the analyses of the experimental results strongly suggest the observed rectification to result from Schottky-type diode properties of SWNTs with mixed chirality along the tube.     

Electrical Properties of Nickel Phthalocyanine Thin Films Using Gold and Lead Electrodes

The electrical properties of nickel phthalocyanine (Ni Pc) thin film sandwich devices have been investigated using gold and lead electrode combinations. At low forward voltages with gold electrode as positive, the device showed rectification properties, while at higher forward voltages the conduction mechanisms were dominated by space charged limited conduction (SCLC) controlled by a single and an exponential trapping levels at two different ranges of applied voltages. Under the reverse bias a Schottky type of conduction process was identified. From our investigations we found that gold electrode acts as an ohmic contact and lead electrodes as a blocking contact to Ni Pc layer with the existence of a barrier region at the lead electrode side of the Ni Pc layer. The effect of oxygen doping on the electrical conductivity of these devices have also been studied. After exposure to dry air for 30 days the device showed a higher order of current both in the forward and reverse bias. In the oxygen doped sample an increase in the rectification ratio and an enhanced value of trap concentrations were observed.     

Germanium on insulator near-infrared photodetectors fabricated by layer transfer

We report on novel pn Ge photodetectors fabricated on glass. The fabrication consists of wafer bonding and layer splitting, followed by a low-temperature epitaxial growth of Ge. The photodiodes are characterized in terms of dark current and responsivity, and their performance compared with devices realized on either Ge or Si. The minimum current density is 50 μA/cm² at 1 V reverse bias, the responsivity is 0.2 A/W in the photovoltaic mode, with a maximum of 0.28 A/W at 1.55 μm at a reverse voltage of 5 V.     

Effect of oxygen annealing on the ultraviolet photoresponse of P-NiO-nanoflower/n-ZnO-nanowire heterostructures

A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O2) ambient exhibited better rectification behavior (I forward/I reverse = 427), a lower forward threshold voltage (V(th) = 0.98 V), a lower leakage current (1.68 x 10(-5) A/cm2), and superior sensitivity (I uv/I dark = 57.8; I visible/I dark = 1.25) to UV light (lambda = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity. A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O2 ambient indicate that they can be applied to nano-integrated optoelectronic devices.     

A.c. and d.c. conduction processes in octakis[(4-tert-butylbenzylthio)-porphyrazinato]Cu(II) thin films with gold electrodes

The d.c. and a.c. electrical transport properties of Au/Pz/Au devices with various thickness of Pz(octakis[(4-tert-butylbenzylthio)-porphyrazinato]Cu(II)) layer have been investigated. Measurements revealed that, in contrast to previously investigated Au/Pc/Au structures, low voltage d.c. behaviour of the films can be described by the field-lowering mechanisms with a log(J) ∝ V ^1/2 current density-voltage characteristics under forward and reverse bias. For high reverse voltages, the observed ln(J/V ²) – 1/V characteristics indicated that the origin of conduction mechanism is Fowler–Nordheim tunnelling (FNT). On the other hand, the voltage dependence of current density at the higher forward-voltage region indicates that the mechanism of conduction in Au/Pz/Au devices is space charge limited conduction dominated by exponential trap distribution. A thickness independent barrier height was observed for tunnelling, while the total trap concentration show a general tendency to decrease with increasing film thickness. The a.c. conductivity showed two regions in the ln(σ _a.c.) – ln( f ) plots having different slopes, leading to the conclusion that for low frequency region, the dominant conduction mechanism is a small polaron tunnelling at all temperatures, whereas for high frequency region, correlated barrier hopping model is the dominant mechanism in the investigated devices.