δ掺杂的赝配HEMTAlGaAs／InGaAs／GaAs结构的光电流谱

本文首次报道了δ掺杂的赝配高电子迁移率晶体管结构（ＨＥＭＴＳ）Ａｌ０．３０Ｇａ０．７０Ａｓ／Ｉｎ０．１５Ｇａ０．８５Ａｓ／ＧａＡｓ的光电流谱研究．实验观察到了ｎ＝１重空穴子带到ｎ＝１电子子带和ｎ＝２电子子带的激子吸收峰以及ＧａＡｓ本征吸收相位变化所引起的光电流结构，并对光电流谱随温度和偏压变化的行为进行了讨论．     

InGaAsP和GaAlAs半导体激光器稳频放电吸收池的研究

本文报导了我们采用“光电流”信号作为频率标准，稳定ＩｎＧａＡｓＰ和ＧａＡｌＡｓ半导体激光器输出光波频率所用的气体放电吸收池的设计与研制结果。     

新的空间调制光谱技术在半导体超晶格量子阱中的应用

报道一种通过转动样品来实现空间调制微分反射（ＤＲ）光谱技术,给出ＧａＡｓ／ＡｌＧａＡｓ多量子阱和应变ＩｎＧａＡｓ／ＧａＡｓ多量子阱在室温下的ＤＲ谱实验测量结果,并与光调制反射谱（ＰＲ）实验和理论计算结果相比较．实验证明ＤＲ谱的信号比ＰＲ谱更强,可达１０－２量级,两者一致并与理论计算结果符合得很好．ＤＲ谱是研究薄膜和微结构的有效方法     

GaAs／AlGaAs多量子阱结构的热电子效应

采用低温荧光激发光谱研究了ＧａＡｓ／ＡｌＧａＡｓ多量子阱结构中热电子的驰豫过程，在ＰＬＥ谱中首次观察到ＧａＡｓ／ＡｌＧａＡｓ多量子阱中ＬＯ声子的发射，用四能带Ｋａｎｅ模型计算了由轻、重空穴杂化效应引起的价带结构的畸变及其对声子发射谱的影响，实验和理论计算结果均表明、光激发热电子可以通过发射ＬＯ声子直接弛豫到激子态上，实现热电子的冷却。     

InAlGaAs/GaAs量子阱的生长及其界面特性

本文研究了以ＩｎＡｌＧａＡｓ作垒层的ＩｎＡｌＧａＡｓ／ＧａＡｓ量子阱的低压金属有机化合物化学汽相淀积（ＬＰ－ＭＯＣＶＤ）生长及其界面特性,发现在适当生长条件下可以解决ＩｎＧａＡｓ和ＡｌＧａＡｓ在生长温度范围不兼容的问题,得到了高质量的ＩｎＡｌＧａＡｓ／ＧａＡｓ量子阱材料．同时用Ｘ光和低温光致发光（ＰＬ）谱研究了量子阱结构的界面特性,表明适当的界面生长中断不仅可以改善界面平整度,而且能改善垒层ＩｎＡｌＧａＡｓ的质量．     

用MOCVD在非平面衬底上生长的量子阱、量子线及其光学性质

本文报道在６５０℃的衬底温度下实现了ＭＯＣＶＤ在（１００）面和（１１１）面上生长ＧａＡｓ与Ａｌ０．４Ｇａ０．６Ａｓ的不同的选择性．这一衬底温度比国际上以前报道的要低，对制作适于光电器件的ＧａＡｓ／ＡｌＧａＡｓ量子阱层比较有利．用此技术，在ＧａＡｓ非平面衬底上生长了ＧａＡｓ／Ａｌ０．４Ｇａ０．６Ａｓ量子阱，并用扫描电镜、低温光致发光谱以及偏振激发的光反射率谱技术进行了研究．结果不仅证明了ＭＯＣＶＤ外延生长ＧａＡｓ和Ａｌ０．４Ｇａ０．６Ａｓ的独特选择性，也证明了在Ｖ字形沟槽底形成了量子线．     

InxGa1—xAs／AlyGa1—yAs多量子阱的高压光致发光研究

用金刚石对顶砧压力装置在浓氮温度下和０～４ＧＰａ的压力范围内测量了不同阱宽（１．７～１１．０ｎｍ）的ＩｎｘＧａ１－ｘＡｓ／ＡｌｙＧａ１－ｙＡｓ（ｘ，ｙ＝０．１５，０；０．１５，０．３３；０，０．３３）多量子阱的静压光致发光谱，发现在Ｉｎ０．１５Ｇａ０．８５Ａｓ／ＧａＡｓ多量子阱中导带第一子带到重空穴第一子带间激子跃迁产生的光致发光峰能量的压力系数随阱宽的增加而减小，在Ｉｎ０．１５Ｇａ０．８５Ａｓ／     

用MOCVD在非平面衬底上生长的量子阱,量子线及其光学性质

本文报道在６５０℃的衬底温度下实现了ＭＯＣＶＤ在（１００）面和（１１１）面上生长ＧａＡｓ与Ａｌ０．４Ｇａ０．６Ａｓ的不同选择性。这一衬底温度比国际上以前报道的要低，对制作适于光电器件的ＧａＡｓ／ＡｌＧａＡｓ量子阱层比较有利。用此技术，在ＧａＡｓ非平面衬底上生长了ＧａＡｓ／Ａｌ０．４Ｇａ０．６Ａｓ量子阱，并用扫描电镜、低温光致发光谱及偏振激发的光反射率谱技术进行了研究。结果不仅证明了ＭＣＣＶＤ外延生     

3～5.3μmIn_xGa_(1-x)As/Al_yGa_(1-y)As/Al_zGa_(1-z)As非对称台阶量子阱红外探测器

本文报道我们率先研制出的３～５．３μｍＩｎｘＧａ１－ｘＡｓ／ＡｌｙＧａ１－ｙＡｓ／ＡｌｚＧａ１－ｚＡｓ非对称台阶量子阱红外探测器的制备和性能．该探测器具有光伏特征，７７Ｋ温度、±７Ｖ外偏压下的５００Ｋ黑体探测率达到约１．０×１０１０ｃｍ·Ｈｚ１／２／Ｗ，并且，与１→２子带间跃迁相对应的光电流峰值响应波长可随外偏压在中红外（３～５．３μｍ）波段作适当调谐．运用平面波展开法，依据样品的阱、垒结构参数，计算了ＩｎｘＧａ１－ｘＡｓ／ＡｌｙＧａ１－ｙＡｓ／ＡｌｚＧａ１－ｚＡｓ非对称台阶量子阱１→２子带间跃迁的Ｓｔａ     

GaAs／AlGaAs单量子阱中界面粗糙度散射

对三种不同生长条件、不同质量的ＧａＡｓ／ＡｌＧａＡｓ单量子阱进行了输运性质和光致发光谱的研究．在低迁移率的样品中，界面粗糙度对二维电子气的散射起主导作用．我们的研究也表明了：采用（ＧａＡｓ）４／（ＡｌＡｓ）２超晶格代替常规的ＡｌＧａＡｓ层，或在异质结界面生长过程中的停顿，都能有效地减少界面粗糙度．     

甚长波量子阱红外探测器中的双激发态工作机理

通过对甚长波量子阱红外探测器的变温变偏压光谱实验,发现了光电流谱峰值响应波长与半高宽随偏置电压和温度变化均会发生变化,尤其以小偏压下峰值移动明显.结合器件能带结构计算的结果,提出了甚长波量子阱红外探测器中双激发态工作模型,并阐明了其中束缚态-准束缚态跃迁模式中准束缚态的物理特性,包括隧穿特性和热离化特性,以及不同工作条件下这两种物理过程在形成光电流时的主导性.同时,验证了甚长波量子阱红外探测器件的第一激发态随外界工作条件的变化会呈现出准束缚到准连续的变化特性.最后,揭示了在甚长波量子阱红外探测器工作中束缚态-准束缚态跃迁工作模式对于降低器件暗电流、提升器件工作温度、提高器件探测率的有效性.     

Wannier-Stark ladder spectra in InxGa1−xAs---GaAs strained layer piezo-electric superlattices

Wannier-Stark ladder transitions in the photocurrent spectra of (111)B In_xGa_1−xAs---GaAs strained layer superlattices are reported. Both vertical transitions in the same well and diagonal transitions between adjacent wells are observed. In contrast to (100) superlattices, the Wannier-Stark spectra are observed for both senses of applied bias relative to zero potential drop across the superlattice. The observed transition energies are found to be in good agreement with the predictions of exciton calculations. The piezo-electric field is deduced in a simple and direct way from analysis of the spectra as a function of bias.     

Observation of a Charge Transfer State in Low‐Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

The presence of charge transfer states generated by the interaction between the fullerene acceptor PCBM and two alternating copolymers of fluorene with donor–acceptor–donor comonomers are reported; the generation leads to modifications in the polymer bandgap and electronic structure. In one of polymer/fullerene blends, the driving force for photocurrent generation, i.e., the gap between the lowest unoccupied molecular orbitals of the donor and acceptor, is only 0.1 eV, but photocurrent is generated. It is shown that the presence of a charge transfer state is more important than the driving force. The charge transfer states are visible through new emission peaks in the photoluminescence spectra and through electroluminescence at a forward bias. The photoluminescence can be quenched under reverse bias, and can be directly correlated to the mechanism of photocurrent generation. The excited charge transfer state is easily dissociated into free charge carriers, and is an important intermediate state through which free charge carriers are generated.     

Strain effect on intersubband transitions in rolled-up quantum well infraredphotodetectors

Pre-strained nanomembranes with four embedded quantum wells (QWs) are rolled up into threedimensional (3D) tubular QW infrared photodetectors (QWIPs),which are based on the QW intersubband transition (ISBT).A redshift of~0.42 meV in photocurrent response spectra is observed and attributed to two strain contributions due to the rolling of the pre-strained nanomembranes.One is the overall strain that mainly leads to a redshift of~0.5 meV,and the other is the strain gradient which results in a very tiny variation.The blue shift of the photocurrent response spectra with the external bias are also observed as quantum-confined Stark effect (QCSE) in the ISBT.     

Photoinduced absorption spectroscopy on MDMO-PPV:PCBM solar cells under operation

Near-steady-state photoinduced absorption (PIA) spectroscopy is employed to study the charge carrier dynamics in polymer:fullerene (poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1-4-phenylene vinylene]: 1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C₆₁; MDMO-PPV:PCBM) solar cells under operating conditions. Artifacts in the PIA spectra originating from thermal heating of the aluminum electrode and from interference of incoming and reflected light waves are analyzed. PIA signals from functioning devices are studied as a function of applied bias and temperature and complemented with photocurrent measurements under identical conditions. Comparison between photocurrent and PIA measurements shows that PIA mainly probes trapped cationic charge carriers while the photocurrent samples mobile carriers. The number density of trap sites is estimated at 10¹⁷ cm⁻³ and trapped carriers can be stabilized by applying a reverse bias potential over the device.     

Electrical and radiation characteristics of semilarge photoconductive terahertz emitters

We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry.     

Reliably designing InGaAs-InAlAs strained multiple-quantum-well structures for amplitude modulation

A simulation of the performance parameters of amplitude modulators was carried out for InGaAs-InAlAs multiple-quantum-well structures for operation at 1.55 /spl mu/m. The device parameters were estimated from the calculated absorption spectra with applied reverse bias and from the photoluminescence spectra. The theoretically determined results are compared with the experimental data obtained from the measured photocurrent spectra with light incident in the direction perpendicular to the layers. Good agreement was achieved between experimental and theoretical data, providing a reliable way for designing efficient amplitude modulators. The effect of residual doping level and pre-bias on device parameters is discussed.     

Correlated and uncorrelated timing jitter in gain-switched laserdiodes

The author describes correlated and uncorrelated timing jitter of gain-switched pulses generated from sinusoidally modulated laser diodes measured from photocurrent power spectra. It is found that if dc bias is decreased to obtain shorter pulses, then the root-mean-square (rms) value of uncorrelated timing jitter drastically increases to more than 2 ps, while correlated jitter remains constant at the drive circuit level of ~0.2 ps. By optimizing the bias condition and compression fiber length, total timing jitter of gain-switched pulses can be reduced to as low as ~0.5 ps, as their pulse width is kept less than 10 ps     

Electroabsorption modulation in strained piezoelectric InGaAs/InPmultiquantum wells operating at λ≈1.55 μm

An investigation of absorption modulation using strained piezoelectric InGaAs/InP multiquantum wells grown on (111)B InP substrates is presented. Strong excitonic features are observed in the room temperature photocurrent spectra for a structure with 50 Å quantum wells under 0.6% compressive strain. The application of a reverse bias results in a large blue-shift of the absorption edge of up to 8 nm/V     

Infrared detection utilizing both intersubband and free-carrier absorption in reverse-biased Superlattice infrared photodetector

Intersubband and free-carrier associated photoresponse in a GaAs-AlGaAs superlattice infrared photodetector is investigated. Under reverse bias, the photodetector is similar to an internal photoemission photodetector and significant photoresponse due to free-carrier absorption at the collector contact is found. In particular, in our photodetector, intersubband transitions at the superlattice layer also play an important role at low reverse biases and produce a photocurrent with an opposite direction to that of the free-carrier associated photocurrent. Since the total photocurrent consists of two components with opposite signs, photocurrent reversal occurs in the response spectrum. At high reverse bias, the intersubband-associated photoresponse is fully suppressed by the blocking barrier and the overall photoresponse is mainly due to the photoemission via free-carrier absorption at the collector contact. The intersubband and free-carrier associated photocurrent components under reverse bias can be resolved from the measured polarization dependence of the spectral response. The analysis of the measured free-carrier associated photocurrent agrees with previous studies on free-carrier absorption. A possible application with our detector to determine the wavelength of a monochromatic light is also demonstrated.