Electroluminescence from modulation-doped pseudomorphic AlGaAs/InGaAs/GaAs quantum wells

Low-temperature electroluminescence (EL) is observed in n-type modulation-doped AlGaAs/InGaAs/GaAs quantum well samples by applying a positive voltage between the semitransparent Au gate and alloyed Au-Ge Ohmic contacts made on the top surface of the samples. We attribute impact ionization in the InGaAs QW to the observed EL from the samples. A redshift in the EL spectra is observed with increasing gate bias. The observed redshift in the EL spectra is attributed to the band gap renormalization due to many-body effects and quantum-confined Stark effect.     

High-performance pyroelectric single crystals for uncooled infrared detection applications

Uncooled pyroelectric infrared detectors based on ferroelectric single crystals 0.74Pb(Mg_1/3Nb_2/3)O₃–0.26PbTiO₃ (PMN–0.26PT) were fabricated. The performances of pyroelectric detectors dependence on detector fabrication temperature, absorption layer, and element thickness were compared. The room-temperature voltage responsivity (R_v) of 200 V/W and specific detectivity (D^*) of 10⁸ cm Hz^1/2/W at 12.5 Hz have been achieved. The results reveal that the better pyroelectric response can be expected by controlling temperature below 70 °C during the fabrication of the pyroelectric detectors, selecting absorption layer with high absorption coefficient, and decreasing the thickness of the elements.     

Effect of hydrogen on modulation-doped AlGaAs/InGaAs/GaAs heterostructures: a photoluminescence study

The effect of hydrogen on donors and interface defects in silicon modulation doped Al_xGa_1−xAs/In_yGa_1−yAs/GaAs heterostructures has been investigated by photoluminescence (PL). Hydrogenation was carried out on two sets of samples, one set consists of high quality pseudomorphic heterostructures and another set having partially lattice relaxed structures prone to the defects. On exposure of high quality pseudomorphic structures to hydrogen plasma above 150 °C, a significant blue shift in the PL peak positions as well as bandwidth narrowing is observed. This indicates, the reduction in two-dimensional electron gas in the In_yGa_1−yAs quantum well due to hydrogen passivation of silicon donors in the Al_xGa_1−xAs supply layer. The reactivation of the donors is observed upon annealing the hydrogenated sample for 1 h at 250 °C under hydrogen ambient. Another interesting feature is a significant improvement in the PL of lattice-relaxed structures upon hydrogenation of the samples above 250 °C, which is attributed to the hydrogen passivation of interface defects due to the misfit dislocations.     

A novel infrared absorbing structure for uncooled infrared detector

In this paper, we proposed a novel infrared absorbing structure for uncooled infrared detectors. The infrared absorber makes use of a quarter-wavelength structure composed of a dielectric layer, a protecting layer, an active layer, a supporting layer and a reflecting layer. Sputtered amorphous silicon is used as a dielectric layer because of its high refractive index. We fabricated the uncooled microbolometer with the proposed infrared absorbing structure by surface micromachining method. Then we characterized various bolometric properties such as thermal conductance, thermal time constant, responsivity and infrared absorptance. The fabricated bolometer showed the thermal conductance of 6.72 × 10⁻⁷ W/K, the thermal mass of 4.43 × 10⁻⁹ J/K, the thermal time constant of 6.6 ms and the responsivity of 7.76 × 10³ V/W at 10 Hz chopper frequency and 9.22 μA bias current. From the results, the estimated absorptance is about 80%. We expect that the proposed absorbing structure shows high infrared absorption and high performance of uncooled microbolometer.     

AlGaAs/InGaAs PHEMT栅电流参数退化模型研究

为定量研究在PHEMT栅电流退化过程中, 不同失效机理对应的参数退化时间常数及退化比例, 本文基于退化过程中物理化学反应中反应量浓度与反应速率的关系, 建立了PHEMT栅电流参数退化模型. 利用在线实验的方法获得PHEMT电学参数的退化规律, 分析参数随时间的退化规律, 得到不同时间段内影响栅电流退化的失效机理, 并基于栅电流参数退化模型, 得到了不同的失效机理对应的参数退化时间常数及退化比例. 关键词： PHEMT 栅电流 肖特基接触 退化模型     

高功率梯度折射率分别限制异质结构InGaAs/AlGaAs应变双量子阱激光器

采用金属有机化合物气相淀积（ Ｍ Ｏ Ｃ Ｖ Ｄ）方法成功地研制了具有两对梯度折射率（ Ｇ Ｒ Ｉ Ｎ）异质结结构的 Ｉｎ Ｇａ Ａｓ／ Ａｌ Ｇａ Ａｓ 应变双量子阱激光器。该激光器的波长为 ９７０～９８２ ｎｍ ,室温连续工作阈值电流密度为１４０ Ａ／ｃｍ ２, 工作在０．９ Ａ 时单面连续输出光功率为５２０ ｍ Ｗ , 工作在２．０ Ａ 时, 连续输出光功率为 １．４９ Ｗ , 最高功率可达 ２．４ Ｗ 。微分量子效率高达０．８３ Ｗ ／ Ａ。     

Asymmetric Fabry-Perot modulators with an InGaAs/AlGaAs active region

Strained layer superlattices have been used as the active region in asymmetric Fabry-Perot cavity optical modulators. The active layer of the Fabry-Perot modulator consisted of a 50 period In_0.15 Ga_0.85As/Al_0.30Ga_0.70As (10nm/10nm) superlattice. These quantum wells operate at typical wavelength of around 960 nm. By varying the length of the Fabry-Perot cavity in the modulator by including AlGaAs space layers of different thicknesses in the cavity, it is shown experimentally that both normally on and normally off devices can be obtained using the same stack of quantum wells. For the first type of device operation, a maximum contrast ratio of 8.3 dB could be measured for a reverse voltage of 7 V at 969 nm, while for the second type, a maximum of 8.9 dB at 957 nm was obtained for a 20 V reverse voltage. Using the same structure with an extra Bragg reflector on top of the quantum well layers to increase the surface reflection, a device with a higher finesse of the cavity was obtained. A maximum contrast ratio of 11.5 dB was measured for a reverse bias voltage of 30 V at 978 nm, with an insertion loss of –4.2dB.     

Time-resolved cathodoluminescence of InGaAs/AlGaAs tetrahedral pyramidal quantum structures

An original time resolved cathodoluminescence set up has been used to investigate the optical properties and the carrier transport in quantum structures located in InGaAs/AlGaAs tetrahedral pyramids. An InGaAs quantum dot formed just below the top of the pyramid is connected to four types of low-dimensional barriers: InGaAs quantum wires on the edges of the pyramid, InGaAs quantum wells on the (111)A facets and segregated AlGaAs vertical quantum wire and AlGaAs vertical quantum wells formed at the centre and at the pyramid edges. Experiments were performed at a temperature of 92 K, an accelerating voltage of 10 kV and a beam probe current of 10 pA. The cathodoluminescence spectrum shows five luminescence peaks. Rise and decay times for the different emission wavelengths provide a clear confirmation of the peak attribution (previously done with other techniques) to the different nanostructures grown in a pyramid. Moreover, experimental results suggest a scenario where carriers diffuse from the lateral quantum structures towards the central structures (the InGaAs quantum dot and the segregated AlGaAs vertical quantum wire) via the InGaAs quantum wires on the edges of the pyramid. According to this hypothesis, we have modeled the carrier diffusion along these quantum wires. An ambipolar carrier mobility of 1400 cm²/V s allows to obtain a good fit to all temporal dependences. PACS 78.67.-n     

AlGaAs/InGaAs/GaAs赝配高电子迁移晶体管的kink效应研究

利用二维器件模拟软件MEDICI对AlGaAs/InGaAs/GaAs赝配高电子迁移晶体管器(PHEMT)件进行了仿真，研究了PHEMT器件的掺杂浓度与电子浓度分布，PHEMT器件内部的电流走向及传输特性，重点研究了不同温度和不同势垒层浓度情况下PHEMT器件的kink效应.研究结果表明：kink效应主要与处于高层深能级中的陷阱俘获/反俘获过程有关，而不是只与碰撞电离有关. 关键词： 高电子迁移率晶体管 kink效应 二维电子气     

Time-resolved photoluminescence spectra of high-density InGaAs/AlGaAs quantum wire structures

We investigated the temperature dependence of the time-resolved photoluminescence (PL) spectra of high-density InGaAs/AlGaAs quantum wire (QWR) distributed-feedback laser structure on a submicron grating. A red-shift of peak in the time-resolved PL after photo-excitation was observed due to the relaxation of the photo-generated excitons from the entire QWR to localized centers at 10 K. On the other hand, at 60 K, no red-shift in the time-resolved PL spectra was observed since the localization centers are thermally activated and the excitons are delocalized.     

High Power 980 nm InGaAs/AlGaAs Strained Quantum Well Lasers

By low-pressure metalorganic chemical vapor deposition (LP-MOCVD) system,InGaAs/AlGaAs graded-index separate-confinement heterostructure strained quantum well lasers are grown with carbon doped the upper cladding layer and the capping layer. Carbon tetracholride (CCl4) is used as the carbon source. 100 μm oxide stripe lasers are fabricated,and the laser output power per facet (uncoated) reaches 1.2 W with 2A injection current under the room temperature continuous wave (CW) operation. The threshold current density is 150 A/cm2 with 1000 μm cavity length. The slope efficiency per facet reaches 0.53W/A,and the total external differential quantum efficiency is above 85%. The relations between the threshold current densities,the differential quantum efficiency and the cavity length are studied.     

High Power 980 nm InGaAs/AlGaAs Strained Quantum Well Lasers

1lntroductionCarhan,aIVcolutnnelement,hasmanyadvantagesinGaAsAlGaAsmaterials,suchasIowdiffudricoefficient,relativelowactivateenergyabout26meV,highincmptiOnconcentratboandhighm0bilityduetothelowcomensaterate.SocarbonhasbeenwidelyusedinGaAsAlGaAsheter0unctionbipoartransistors(HBT),modulationdoPingfieldeffecttransistors(m),tunneldiodes,iInPurityinducedlayerdisorderinglaserdiodeS,anddistributedBraggreflectors(DBRs)intheverticalcavitysurfaceedrittinglasers(VCSEL).Ingeneral,therearesever…     

The beam properties of high-power InGaAs/AlGaAs quantum well lasers

The vertical beam quality factor of the fundamental TE propagating mode for InGaAs/AlGaAs SCH DQW lasers emitting at 940 nm is investigated by using the transfer matrix method and the non-paraxial vectorial moment theory for non-paraxial beams. An experimental approach is given for the measurement of the equivalent vertical beam quality factor of an InGaAs/AlGaAs SCH DQW laser. It has been shown that the vertical beam quality factor M_x² is always larger than unity, whether the thickness of the active region of LDs is much smaller than the emission wavelength or not.     

High performance uncooled InAsSbP/InGaAs photodiodes for the 1.8–3.4 μm wavelength range

Room temperature In_0.97Ga_0.03As photodiodes with an InAs_0.36Sb_0.20P_0.44 transparent window layer operating in the mid-infrared region over the wavelength range 1.8–3.4 μm are reported. The InAs_0.36Sb_0.20P_0.44/In_0.97Ga_0.03As heterojunction photodiodes were grown on p-type (100) InAs substrates by liquid phase epitaxy (LPE). Basic detector characteristics have been measured and compared with other detectors in this wavelength range. The typical detectivity of the photodiodes is 1.2 × 10¹⁰ cm Hz^1/2/W at room temperature, which compares very favourably with that of TE cooled HgCdTe and is at least three times that of cooled PbSe photoconductors. The InAs_0.36Sb_0.20P_0.44/In_0.97Ga_0.03As heterojunction photodiodes offer the advantage of increased sensitivity and extended wavelength response at room temperature compared with that of currently available commercial photodetectors, making them an attractive alternative for a number of mid-infrared applications including optical gas sensors and infrared spectrometers.     

Theoretical analysis and experimental application of CDS CMOS integrated circuit for uncooled infrared focal plane arrays

In this paper, a typical correlated double sampling (CDS) complementary metal oxide semiconductor (CMOS) circuit for uncooled infrared focal plane array (IRFPA) is theoretically analyzed, the key factor of CDS CMOS integrated circuit is pointed out, and a new CDS integrated circuit which is high correlative for low-frequency noise is applied in an experimental readout chip for uncooled IRFPA. Theoretical analysis indicates that the sample transfer function of a noise source acted on by CDS processing is related to noise frequency and sampling time interval and the key factor of CDS circuit for reducing or eliminating noise in readout integrated circuit is the sampling time interval. The experimental readout chip with high noise-correlative CDS integrated circuit is fabricated to verify the theoretical analysis, which can be applied to uncooled IRFPAs.     

Quantized conductance in extended electron waveguides fabricated on shallow etched modulation-doped GaAs/AlGaAs heterostructures

By high-resolution electron beam lithography and wet chemical etching extended electron waveguides with lengths up to 20 μm were fabricated on modulation-doped GaAs/AlGaAs heterostructures showing conductance quantization. For short electron waveguides 15 well-resolved steps in the conductance trace are observable. Conductance quantization is observed up to wire lengths comparable to the transport mean free path of electrons in the unconstrained two-dimensional electron gas, indicating that scattering due to fabrication induced defects is negligible in the present structures. By an analysis of temperature-dependent measurements the one-dimensional subband spacings are determined to be greater than 10 meV.     

Point defects and amplification in active layers of InGaAs/AlGaAs heterostructures

The energy levels of gallium and arsenic vacancies as well as silicon impurities in the band gap of In _x Ga_{1 ? x} As have been found as functions of the indium content. The effect of defects on the lasing output power and on the optimal reflection coefficient of output mirrors of laser diode arrays (LDAs) based on the In_0.11Ga_0.89As/AlGaAs heterostructures has been estimated. It has been shown that the lasing output power of LDAs whose active level contains defects with deep energy levels in the band gap is substantially lower (with other conditions being the same) than that of LDAs with shallow level defects in their active layers.     

Role of nitrogen in the mobility drop of electrons in modulation-doped GaAsN/AlGaAs heterostructures

We report transport properties of a 2 dimension electron gas (2DEG) in molecular beam epitaxy-grown GaAs_1−xN_x/AlGaAs modulation-doped heterostructures. Quantum oscillations in far infrared cyclotron resonance prove the efficient electron transfer and formation of the 2DEG. The 2DEG mobility strongly depends on the N concentration in the channel layer. It shows a drastic decrease as compared to N-free samples, even for the smallest amount of N (0.02%). For this N composition, the electron effective mass was found to be 0.073m₀. Reduced growth temperature (450 °C) was found to improve the mobility of N-containing channels. Examination of transport properties from 4 to 300 K and cyclotron resonance experiments give evidence of the presence of ionised impurity-like scattering centres in GaAsN.