基于电容和电导特性分析GaN蓝光发光二极管老化机理

采用正向交流小信号方法测试和分析老化前后GaN发光二极管（LED）的电容-电压特性,结合串联电阻、理想因子、隧穿电流参数讨论负电容以及电导变化情况.基于L-V曲线定性分析老化前后负电容的阈值电压,老化之后样管的受主浓度降低,辐射复合概率下降,大量缺陷以及非辐射复合中心出现,对载流子俘获作用增强,造成负电容降低.反向偏压以及小正向偏压下,隧穿效应导致老化之后样管的电导增大;正向偏压大于2.2 V区域,考虑串联电阻效应,老化后样管电导减小.在分析LED电容-电压、光输出、电学特性曲线与老化机理基础上,通过实验论证以及理论解释表明,负电容以及电导特性可作为分析LED老化特性的参考依据. 关键词： GaN发光二极管 负电容 电导 老化机理     

Properties of Mott contacts with an ultralow metal-semiconductor barrier

The current-voltage and capacitance characteristics of Mott contacts with an ultralow metal-semiconductor barrier are investigated. The analysis is based on the analytical solution of the Poisson equation for the space charge of carriers in the “metal-i-layer-n ⁺-substrate” structure without regard for bulk doping of the i layer. For contacts with ultralow metal-semiconductor barriers (comparable in magnitude to the thermal energy of charge carries), it is demonstrated that the reverse current becomes greater than the forward current, the sign of rectification is reversed, and the capacitance of the contact acquires a strong dependence on the voltage. This means that the mechanism of nonlinearity of the structure changes and the nonlinearity governed by charge carriers injected into the i layer becomes dominant. In a specific range of bias voltages close to zero, the differential resistance and the capacitance of the structure exponentially increase with increasing voltage. The observed behavior is not typical of conventional metal-semiconductor contacts. The obtained dependences of the electric current and capacitance on the voltage determine the characteristics of new advanced instruments, in particular, highly sensitive microwave detectors operating without a bias voltage.     

GaN发光二极管表观电容极值分析

利用正向交流(ac)小信号方法对GaN发光二极管的电容-电压特性进行测量,可以观察到GaN发光二极管中的负电容现象。正向偏压越大,测试频率越低,负电容现象越明显。测量到的负电容现象是表象,不存在负电容;提出GaN发光二极管p-n结的结电容在特定的正向电压范围内等效于可变电容。分析可变电容对正向交流小信号响应得到:特定参数的可变电容使结电容电流相位落后于交流小信号电压相位π/2,使得在测量中表现为负电容。发现表观电容-正向电压曲线的极值点与理论模型相吻合,证明了该理论模型的正确性。     

GaN发光二极管表观电阻极值分析

利用正向交流(ac)小信号方法对GaN发光二极管的电容-电压特性进行测量,可以观察到GaN发光二极管中的负电容现象。利用LED串联等效电路对表观电容和表观电阻进行了测量,表观电阻-正向电压曲线出现了一个极值点。通过对相关文献分析,提出负电容现象的根本原因是在较高的正偏下微分电容dQ/dU<0;推论出pn结的微分电容先随正向偏压的增大而急剧增大,当出现复合发光后随正向偏压的增大而减小,直到随正向偏压的增大而出现负值;正向偏置电压较大时,结电导电流的变化率根据I-V特性曲线取极大值,此时微分电容由于强复合效应已快速变小,表观电阻有极大值;得到了表观电阻极大值表达式。表观电阻与正向电压曲线的极值点与理论模型相吻合,证明了该理论模型的正确性。     

不同负载下直流偏磁对特高压变压器各侧绕组电流影响的计算及分析

基于特高压变压器的时域场路耦合模型, 利用磁场模型中的能量扰动原理以及电路模型中动态电感参数建立瞬态电路偏微分方程模型。对特高压变压器负载时绕组电流受直流偏磁的影响进行了仿真计算, 针对阻性、感性和容性三种不同负载类型, 对绕组电流进行了直流偏磁计算, 并对其各次谐波变化进行了分析。面对特高压变压器大电感、小电阻带来的极为漫长的过渡过程以及直流偏磁计算易被淹没的难点, 通过在电路模型中增加串联电阻, 使达到稳态的时间大大缩短, 并通过电压迭代补偿, 有效消除增大串联电阻值导致的计算偏差, 通过对比所加偏置电流值与串联绕组中的直流分量值验证了本文模型的正确性。     

Physical modeling of direct current and radio frequency characteristics for In P-based InAlAs/InGaAs HEMTs

Direct current(DC) and radio frequency(RF) performances of InP-based high electron mobility transistors(HEMTs)are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley–Read–Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover,the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency( f_(max)) of 385 GHz.     

The origin of negative capacitance in Au/n-GaAs Schottky barrier diodes (SBDs) prepared by photolithography technique in the wide frequency range

Capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements of the Au/n-GaAs Schottky barrier diodes (SBDs) in the wide frequency range of 10 kHz–10 MHz at room temperature were carried out in order to evaluate the reason of negative capacitance (NC). Experimental results show that C and G/ω are strong functions of frequency and bias voltage especially in the accumulation region. NC behavior was observed in the C–V plot for each frequency and the magnitude of absolute value of C increases with decreasing frequency in the forward bias region. Contrary to C, G/ω increases with decreasing frequency positively in this region. NC behavior may be explained by considering the loss of interface charges at occupied states below Fermi level due to impact ionization processes. Such behavior of the C and G/ω values can also be attributed to the increase in the polarization especially at low frequencies and the introduction of more carriers in the structure. The values of R_s decrease exponentially with increasing frequency according to literature. In addition, the values of C and G/ω at 1 MHz were corrected to obtain the real diode capacitance by taking the effect of R_s into account.     

Harmonic and intermodulation performance of optical-fiber Mach–Zehnder microphone

In this paper, closed-form mathematical expressions are obtained for the amplitudes of the harmonic and intermodulation products of the fiber optic Mach–Zehnder microphone excited by a multitone acoustical perturbation. The results show the strong dependence of the harmonic and intermodulation performance on the amplitude of the acoustical perturbation tones and the phase shift produced by the DC bias voltage applied to the reference fiber of the Mach–Zehnder interferometer. The results also show that depending on the phase shift produced by the DC bias voltage, either the third-order or the second-order intermodulation will be dominant. Compared to previously published results for other types of microphones, it appears that the phase shift produced by the DC bias voltage plays an important role in deciding the order of the dominant intermodulation product.     

发光二极管放电实验现象分析

利用直流电源对发光二极管(LED)的结电容充电,切断直流电源后对LED的电压-时间特性进行测量。当充电电压低于LED复合发光的门槛电压,LED的电压-时间特性与普通二极管的相似。当充电电压高于LED复合发光的门槛电压,首次观察到:开始放电的瞬间会出现一个快速下降过程,快速下降到门槛电压以下;LED上的电压越高,快速下降到的电压越低。对该现象进行分析,得到一些新的结论。当LED的正偏电压高于复合发光的门槛电压后,出现了注入到扩散区的非平衡载流子随正偏电压的提高而减小的现象,即dQ/du<0。     

光时分复用(OTDM)系统中基于电吸收调制器(EAM)的短脉冲光源及解复用器的设计考虑

研究了电吸收调制器（ＥＡＭ） 的衰减随外加反向电压增加而指数增加的情形下,短脉冲光源的脉冲输出和解复用器的开关窗口对ＥＡＭ 的消光效率、反向ＤＣ 偏置电压以及正弦ＲＦ 驱动信号的幅度等参量的依赖关系－ 在基于ＥＡＭ 的短脉冲光源中,输出脉冲的消光比等于ＥＡＭ 消光效率η与正弦驱动电压峰峰值Ｖｐｐ 的乘积,输出光脉冲的消光比和脉宽均与ＥＡＭ 的反向偏置电压无关,但输出脉冲的峰值功率与η、Ｖｐｐ 和Ｖｂ 都有关系－ 在基于ＥＡＭ的解复用器中,为了使解复用器的开关窗口近似为矩形,可利用ＥＡＭ 的削波效应,使Ｖｐｐ／２＞ Ｖｂ－ 在ＥＡＭ 的消光效率η已知时,通过仔细设计反向ＤＣ 偏置电压Ｖｂ 和正弦驱动电压的峰峰值Ｖｐｐ ,达到ＯＴＤＭ 解复用器所需要的开关窗口形状、宽度和消光比－     

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si-O-Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.     

GaN发光二极管的负电容现象

采用串联等效电路分析了较大正向电压下半导体二极管的交流电学特性．由此可以同时测量结电容和串联电阻,并能判断二极管是否有界面层。首次发现了在较低的测试频率和较大的正向电压下,GaN二极管的结电容具有负值,并且测试频率越低,正向偏压越大,负电容现象越显著。这种负电容效应可能与大正向电压下强注入造成的电子-空穴复合发光有关。     

Electrical and electroluminescent properties of InAsSb-Based LEDs (λ = 3.85–3.95 μm) in the temperature interval 20–200°C

The temperature dependences of the electrical and electroluminescent properties of InAsSbP/InAsSb/InAsSbP heterostructure LEDs (λ ≈ 3.8−4.0 μm) are studied in the temperature interval 20–200°C. It is shown that the radiation power decreases with increasing temperature in a superexponential manner and that this decrease is associated primarily with a rise in the rate of Auger recombination. The position of the maximum in the radiation spectrum varies with temperature nonmonotonically, since radiative recombination is observed both in the active region and in the wide-gap layer. At room temperature, current through the heterostructure is tunneling current irrespective of the applied voltage polarity. As the temperature rises, either the thermal emission of charge carriers appears (direct bias) or the diffusion current becomes significant (reverse bias).     

Current-confined-path (CCP) giant magnetoresistive (GMR) sensors

Current-perpendicular-to the plane (CPP) giant magnetoresistive (GMR) sensors with a current-confined-path (CCP) layer inserted within the Cu spacer have been manufactured using ultrahigh vacuum PVD sputtering, photolithography, and ion milling processes. Compared with a pure metallic CPP system, the CCP insertion layer enables a substantial increase in sensor resistance with an equivalent or better GMR ratio, and thus a significant improvement in the ΔRA amplitude. Heads with such a sensor have been tested under various bias currents, both quasistatically and on a spinstand. It was found that the resistance of the sensors increases with increasing bias current and voltage, following typical metallic behavior. Also, the CCP insertion layer enables operation at higher bias currents compared with the pure metallic sensors (without the insertion layer) and thus a higher output signal. This effect is attributed to less magnetic instability due to the reduced Ampere fields around the narrow (∼6 nm) current-confined paths. Finally, the CPP-GMR heads with CCP layer were tested under high-density recording conditions using the perpendicular recording media. Bit error rate (BER) as a function of linear density is reported. Microtrack profiles were also recorded to determine track density capability.     

PIN光电探测器的建模与仿真分析

为了优化PIN光电探测器响应特性,首先依据载流子速率方程,并考虑芯片寄生参量和封装寄生参量,建立光电探测器的等效电路模型。然后仿真分析了反偏电压、I区宽度、光敏面、芯片寄生电阻和电容、封装寄生电阻、电容和电感对光电探测器脉冲响应特性和频率响应特性的影响。结果表明:通过增大反偏电压,减小光敏面和寄生参量(芯片寄生电容和电阻,封装寄生电容和电阻),选取合适的I区宽度,利用引线电感的谐振效应现象,可以抑制脉冲响应波形畸变,提高频率响应带宽。     

驱动电压和主体材料对染料掺杂有机电致发光器件的影响

采用对比使用掺杂系统的有机电致发光器件(OLEDs)在不同偏置电压下电致发光(EL)光谱的方法,观察了主体材料8-hydroxyquinoline aluminum(Alq3)中掺杂红色荧光染料4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4Hpyran(DCJTB)发射光谱的变化,研究了偏置电压对掺杂系统中载流子复合区域的影响。另外,通过对比采用不同主体材料的掺杂系统的电致发光(EL)和光致发光(PL)光谱,讨论了主体材料Alq3和N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′-diamine(NPB)不同的掺杂效果。结果表明,随着偏置电压的增大,使用掺杂系统的器件中载流子复合区域逐渐向空穴传输层(HTL)移动,作为主体材料应具有高的能量传递效率,且应对染料具有低的浓度猝灭效应。     

光时分复用(OTDM)系统中基于电吸收调制器(EAM)的短脉冲光源及解复用器的设计考虑

研究了电吸收调制器(EAM)的衰减随外加反向电压增加而指数增加的情形下,短脉冲光源的脉冲输出和解复用器的开关窗口对EAM的消光效率、反向DC偏置电压以及正弦RF驱动信号的幅度等参量的依赖关系.在基于EAM的短脉冲光源中,输出脉冲的消光比等于EAM消光效率η与正弦驱动电压峰峰值V_pp的乘积,输出光脉冲的消光比和脉宽均与EAM的反向偏置电压无关,但输出脉冲的峰值功率与η、V_pp和V_b都有关系.在基于EAM的解复用器中,为了使解复用器的开关窗口近似为矩形,可利用EAM的削波效应,使V_pp/2>V_b.在EAM的消光效率η已知时,通过仔细设计反向DC偏置电压V_b和正弦驱动电压的峰峰值V_pp,达到OTDM解复用器所需要的开关窗口形状、宽度和消光比.     

Actions of negative bias temperature instability (NBTI) and hot carriers in ultra-deep submicron p-channel metal——oxide——semiconductor field-effect transistors (PMOSFETs)

Hot carrier injection (HCI) at high temperatures and different values of gate bias V_g has been performed in order to study the actions of negative bias temperature instability (NBTI) and hot carriers. Hot-carrier-stress-induced damage at V_g=V_d, where V_d is the voltage of the transistor drain, increases as temperature rises, contrary to conventional hot carrier behaviour, which is identified as being related to the NBTI. A comparison between the actions of NBTI and hot carriers at low and high gate voltages shows that the damage behaviours are quite different: the low gate voltage stress results in an increase in transconductance, while the NBTI-dominated high gate voltage and high temperature stress causes a decrease in transconductance. It is concluded that this can be a major source of hot carrier damage at elevated temperatures and high gate voltage stressing of p-channel metal--oxide--semiconductor field-effect transistors (PMOSFETs). We demonstrate a novel mode of NBTI-enhanced hot carrier degradation in PMOSFETs. A novel method to decouple the actions of NBTI from that of hot carriers is also presented.     

The effect of bias voltage on SPRITE detector Modulation Transfer Function (MTF)

The ‘SPRITE’ detector provides time delay and integration in a single-element IR detector. The detector operates by sweeping out photogenerated carriers before recombination occurs and the shape of the line spread function is dependent on the carrier transit time. This paper analyses the variation of the line spread function with the detector bias voltage and presents predicted detector modulation transfer functions (MTF) based on this analysis. The results obtained indicate that some improvement in the mid-band MTF may be achieved by increasing the detector bias voltage.     

NPB厚度对异质结OLED载流子复合区域的调控

通过调控p型半导体N,N′-bis(naphthalen-1-y)-N,N′-bis(phenyl)benzidine(NPB)层的厚度,制备了结构为ITO/NPB/aluminum(Ⅲ)bis(2-methyl-8-quinolinato)-4-phenylphenolate(BAlq)/NPB(0~18nm)/tri-(8-hydroxyquinoline)-aluminum(Alq₃)/Mg:Ag的多层有机电致发光器件.分析结果表明,在该类异质结器件中,NPB不仅可以作为空穴传输材料,在适当的厚度范围内,它还可以起到调控载流子复合区域的作用;当NPB厚度在0~18nm之间变化时,随着其厚度增加器件发光颜色可由蓝色变为绿色.通过器件发光光谱的表征可以得知,器件的载流子复合区域相应地由BAlq层转移至Alq₃层.