利用In0.82Ga0.18As与InP衬底之间的应力制作结构材料的缓冲层

采用低压金属有机化学气相淀积(LP-MOCVD)技术,在InP(100)衬底上生长In0.82Ga0.18As,研究生长温度对In0.82Ga0.18As材料表面形貌、结晶质量和电学性能的影响.利用InP(100)衬底与In0.82Ga0.18As材料晶格失配所产生的应变,在不同的生长温度下应变释放程度不同,进而在In...     

缓冲层InxGa1-xAs组分对In0.82Ga0.18As结晶质量和表面形貌的影响

采用低压金属有机化学气相沉积(LP-MOCVD)技术,两步生长法在InP衬底上制备In_0.82Ga_0.18As材料.研究缓冲层In_xGa_1-xAs的In组分对In_0.82Ga_0.18As结晶质量和表面形貌的影响.X射线衍射(XRD)用于表征材料的组分和结晶质量.用扫描电子显微镜(SEM)观察样品的表面形貌.实验结果表明,低温生长的缓冲层In_xGa_1-xAs的In组分影响高温生长的外延层In_0.82Ga_0.18As的结晶质量和表面形貌.测量得到四个样品的外延层In_0.82Ga_0.18As的X射线衍射谱峰半峰全宽(FWHM)为0.596°,0.68°,0.362°和0.391°,分别对应缓冲层In组分x=0.28,0.53,0.82,0.88,当缓冲层In组分是0.82时,FWHM最窄,表明样品的结晶质量最好.SEM观察四个样品的表面形貌,当缓冲层In组分是0.82时,样品的表面平整,没有出现交叉平行线或蚀坑等缺陷,表面形貌最佳.     

空间用GaInP/GaAs/In0.3Ga0.7 As(1 eV)倒装三结太阳电池研制

采用阶变缓冲层技术 (step-graded) 外延生长了具有更优带隙组合的倒装GaInP/GaAs/In_0.3Ga_0.7As(1.0 eV) 三结太阳电池材料, TEM和HRXRD测试表明晶格失配度为2%的In_0.3Ga_0.7As 底电池具有较低的穿透位错密度和较高的晶体质量, 达到太阳电池的制备要求. 通过键合、剥离等工艺制备了太阳电池芯片. 面积为 10.922 cm² 的太阳电池芯片在空间光谱条件下转换效率达到32.64% (AM0, 25 ℃), 比传统晶格匹配的 GaInP/GaAs/Ge(0.67 eV) 三结太阳电池的转换效率提高3个百分点. 关键词： 太阳电池 三结 倒装结构     

Surface deformation phenomena induced by electron-beam irradiation in strained InGaAs/AlGaAs layers on GaAs (1 0 0) and (3 1 1)B substrates

The strained InGaAs/AlGaAs layer structures have been grown on GaAs ( 10 0) and (3 1 1)B substrates in a horizontal low-pressure metalorganic vapor-phase epitaxy system at a temperature of 800°C. In the surface observation using a high-resolution scanning electron microscope, we have found that surface deformation phenomena induced by electron-beam irradiation in strained In_0.36Ga_0.64As,/Al_0.3Ga_0.7As layers on GaAs (1 0 0) and (3 1 1)B substrates. The change of the surface morphology was observed in real time on the display of SEM with the accelerating voltage of 30 kV and the irradiated time of 60–120 s. The surface deformation through mass transport seems to be the cause of the residual strain relaxation due to electron-beam irradiation.     

空间用倒装三结太阳能电池及其抗辐射性能研究

使用金属有机化学气相沉积技术,在4英寸GaAs衬底上获得了空间用GaInP/GaAs/In_(0.3)Ga_(0.7)As倒装三结太阳能电池.高分辨X射线衍射和阴极射线发光测试结果表明AlInGaAs应力渐变缓冲层的晶格弛豫度约100%,其整面平均穿透位错密度约5.4×10~6/cm~2.与GaInP/InGaAs/Ge常规三结太阳能电池相比,在AM0光谱、25℃测试条件下,面积24 cm~2的倒装三结太阳能电池转换效率达到32%,输出功率提高了5%.采用1 MeV高能电子对倒装三结电池进行粒子辐照测试,电池各项性能参数随不同辐照剂量发生改变,在1×10~(15)/cm~2辐照总剂量下电池转换效率衰降比例达到15%.     

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.     

Surface morphology of InGaAs on GaAs(100) by chemical beam epitaxy using unprecracked monoethylarsine, triethylgallium and trimethylindium

Temperature-dependent evolution of surface corrugation and the interface dislocation in In_0.15Ga_0.85As epilayer on GaAs(100) substrate grown by chemical beam epitaxy using unprecracked monoethylarsine have been investigated by atomic force microscope (AFM) and transmission electron microscopy (TEM). AFM images showed that the line direction of surface ridge changes from [011] to [0 1] with increasing temperature. However, TEM micrographs showed that dislocation networks are formed along both [011] and [0 1] directions at the interface. These results indicate that growth kinetics on the terrace and at surface steps generated by the dislocations play an important role in determining the direction of surface corrugation. We suggest that the temperature-dependent change of surface corrugation is caused by an anisotropic surface diffusion on the terrace and different sticking probability of adsorbates on the surface steps which were produced by interface misfit dislocation along the two orthogonal surface directions.     

Growth condition optimization and mobility enhancement through inserting AlAs monolayer in the InP-based In_xGa_(1-x)As/In_(0.52)Al_(0.48)As HEMT structures

The structure of In P-based In_xGa_(1-x) As/In0.52Al0.48 As pseudomorphic high electron mobility transistor(PHEMT)was optimized in detail.Effects of growth temperature,growth interruption time,Si δ-doping condition,channel thickness and In content,and inserted Al As monolayer(ML) on the two-dimensional electron gas(2DEG) performance were investigated carefully.It was found that the use of the inserted Al As monolayer has an enhancement effect on the mobility due to the reduction of interface roughness and the suppression of Si movement.With optimization of the growth parameters,the structures composed of a 10 nm thick In0.75Ga0.25 As channel layer and a 3 nm thick Al As/In0.52Al0.48 As superlattices spacer layer exhibited electron mobilities as high as 12500 cm~2·V-1·s~(-1)(300 K) and 53500 cm~2·V~(-1_·s~(-1)(77 K) and the corresponding sheet carrier concentrations(Ns) of 2.8×10~(12)cm~(-2)and 2.9×1012cm~(-2),respectively.To the best of the authors' knowledge,this is the highest reported room temperature mobility for In P-based HEMTs with a spacer of 3 nm to date.     

Improved thermal property of strained InGaAlAs/AlGaAs quantum wells for 808-nm vertical cavity surface emitting lasers

The 808-nm vertical cavity surface emitting laser (VCSEL) with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is designed and fabricated. Compared with the VCSELs with Al_0.05Ga_0.95As/Al_0.3Ga_0.7As quantum wells, the VCSEL with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is demonstrated to possess higher power conversion efficiency (PCE) and better temperature stability. The maximum PCE of 43.8% for 10-μm VCSEL is achieved at an ambient temperature of 30 ℃. The size-dependent thermal characteristics are also analyzed by characterizing the spectral power and output power. It demonstrates that small oxide-aperture VCSELs are advantageous for temperature-stable performance.     

Non-destructive characterisation of (Ga,In,Al,As,P)-based ternary multilayer structures using spectroscopic ellipsometry

Spectroscopic ellipsometry has been used to measure compositions and layer thicknesses of two-, three- and four-layer structures consisting of Al_0.2Ga_0.8As/GaAs and In_0.53Ga_0.47As/Al_0.48In_0.52As/InP materials. A simple procedure has been developed to obtain Al_0.48In_0.52As dielectric functions by scaling InP values. Very good agreement has been obtained with destructive techniques.     

Combined effects of substrate compliance and film compositional grading on strain relaxation in layer-by-layer semiconductor heteroepitaxy: the case of InAs/In0.50Ga0.50As/GaAs(1 1 1)A

A systematic theoretical analysis is presented of the combined effects of substrate compliance and film compositional grading on the relaxation of strain due to lattice mismatch in layer-by-layer semiconductor heteroepitaxy. The analysis is based on a combination of continuum elasticity theory and a novel atomistic simulation approach for modeling structural and compositional relaxation in layer-by-layer heteroepitaxial systems. Results are presented for InAs epitaxy on GaAs(1 1 1)A compliant substrates with some marginal film compositional grading that consists of one monolayer of In_0.50Ga_0.50As grown on the substrate surface prior to InAs growth. A parametric study is carried out over a wide range of substrate thicknesses. Interfacial stability with respect to misfit dislocation formation, the dependence on substrate thickness of a thermodynamic critical film thickness, and the completion of the coherent-to-semicoherent interfacial transition are examined in detail. In addition, the structural characteristics and compositional distribution of the corresponding semicoherent interfaces, the associated strain fields, as well as the film surface morphological characteristics are analyzed. Most importantly, the role of segregation at defects of a semicoherent interface in the thermodynamics of layer-by-layer heteroepitaxial growth is demonstrated. Our study shows that systematic combination of the mechanical behavior of thin compliant substrates with grading of the epitaxial film composition provides a very promising engineering strategy for strain relaxation in heteroepitaxy.     

Molecular beam epitaxy growth and characterization of self-assembled InAs quantum dots on (1 0 0) InAlAs/InP substrates

Self-assembled InAs quantum dots (QDs) on In_0.52Al_0.48As layer lattice matched to (1 0 0) InP substrates have been grown by molecular beam epitaxy (MBE) and evaluated by transmission electron microscopy (TEM) and photoluminescence (PL). TEM observations indicate that defect-free InAs QDs can be grown to obtain emissions over the technologically important 1.3–1.55 μm region. The PL peak positions for the QDs shift to low energy as the InAs coverage increases, corresponding to increase in QD size. The room temperature PL peak at 1.58 μm was observed from defect-free InAs QDs with average dot height of 3.6 nm.     

Structural characterization of Al_(0.55)Ga_(0.45)N epitaxial layer determined by high resolution x-ray diffraction and transmission electron microscopy

Structural characteristics of Alo.55 Gao.45N epilayer were investigated by high resolution x-ray diffraction(HRXRD)and transmission electron microscopy(TEM);the epilayer was grown on GaN/sapphire substrates using a high-temperature A1 N interlayer by metal organic chemical vapor deposition technique.The mosaic characteristics including tilt,twist,heterogeneous strain,and correlation lengths were extracted by symmetric and asymmetric XRD rocking curves as well as reciprocal space map(RSM).According to Williamson-Hall plots,the vertical coherence length of AlGaN epilayer was calculated,which is consistent with the thickness of AlGaN layer measured by cross section TEM.Besides,the lateral coherence length was determined from RSM as well.Deducing from the tilt and twist results,the screw-type and edge-type dislocation densities are 1.0×10~8 cm~(-2) and 1.8×10~(10) cm~(-2),which agree with the results observed from TEM.     

Occurrence and elimination of in-plane misoriented crystals in AlN epilayers on sapphire via pre-treatment control

AlN epilayers are grown directly on sapphire(0001)substrates each of which has a low temperature AlN nucleation layer.The effects of pretreatments of sapphire substrates,including exposures to NH3/H2and to H2only ambients at different temperatures,before the growth of AlN epilayers is investigated.In-plane misoriented crystals occur in N-polar AlN epilayers each with pretreatment in a H2only ambient,and are characterized by six 60°-apart peaks with splits in each peak in(10ˉ12)phi scan and two sets of hexagonal diffraction patterns taken along the[0001]zone axis in electron diffraction.These misoriented crystals can be eliminated in AlN epilayers by the pretreatment of sapphire substrates in the NH3/H2ambient.AlN epilayers by the pretreatment of sapphire substrates in the NH3/H2ambient are Al-polar.Our results show the pretreatments and the nucleation layers are responsible for the polarities of the AlN epilayers.We ascribe these results to the different strain relaxation mechanisms induced by the lattice mismatch of AlN and sapphire.     

内嵌InAs量子点的δ掺杂GaAs/AlxGa1-xAs二维电子气特性分析

采用分子束外延技术对δ掺杂GaAs/Al_xGa_1-xAs二维电子气(2DEG)样品进行了生长. 在样品生长过程中, 分别改变掺杂浓度(N_d)、空间隔离层厚度(W_d) 和Al_xGa_1-xAs中Al组分(x_Al)的大小, 并在双温(300 K, 78 K)条件下对生长的样品进行了霍尔测量; 结合测试结果, 分别对N_d, W_d及x_Al与GaAs/Al_xGa_1-xAs 2DEG的载流子浓度和迁移率之间的关系规律进行了细致的分析讨论. 生长了包含有低密度InAs量子点层的δ掺杂GaAs/Al_xGa_1-xAs 2DEG 样品, 采用梯度生长法得到了不同密度的InAs量子点. 霍尔测量结果表明, 随着InAs量子点密度的增加, GaAs/Al_xGa_1-xAs 2DEG的迁移率大幅度减小, 实验中获得了密度最低为16×10⁸/cm²的InAs量子点样品. 实验结果为内嵌InAs量子点的δ掺杂GaAs/Al_xGa_1-xAs 2DEG的研究和应用提供了依据和参考. 关键词： 二维电子气 InAs量子点 载流子浓度 迁移率     

Dislocation distributions and tilts in Al(Ga)InAs reverse-graded layers grown on misorientated GaAs substrates

Compositionally undulating step-graded Al(Ga)In_xAs(x = 0.05–0.52) buffers with the following In P layer were grown by metal–organic chemical vapor deposition(MOCVD) on(001) GaAs with a 15°miscut. The dislocation distribution and tilts of the epilayers were examined using x-ray rocking curve and(004) reciprocal space maps(RSM) along two orthogonal 《110》 directions. The results suggested that such reverse-graded layers have different effects on α and βdislocations. A higher dislocation density was observed along the [110] direction and an epilayer tilt of-1.43°was attained in the [1-10] direction when a reverse-graded layer strategy was employed. However, for conventional step-graded samples,the dislocation density is normally higher along the [1-10] direction.     

Femtosecond laser spectroscopy of In0.53Ga0.47As/InP multiple quantum wells: interfacial roughness and photoexcited carrier relaxation

Interfacial properties and relaxation dynamics of photoexcited carriers in In_0.53Ga_0.47As/InP multiple quantum wells (MQWs) have been investigated by means of cross-sectional scanning tunneling spectroscopy and optical spectroscopy methods (luminescence, absorption and pump–probe experiments). The MQW structure consists of 125 periods of 10-nm-wide well layers and 40-nm-wide barrier layers on an InP(0 0 1) substrate. The observed interfacial roughness of the InGaAs-on-InP is 1–2 monolayers (ML), while that of the InP-on-InGaAs is 3–4 ML. The Stokes shift observed in luminescence and absorption spectra at 77 K corresponds well to the well-width distribution observed by the cross-sectional STM. Differential absorption spectra measured by pump–probe spectroscopy show that relaxation of hot carriers in conduction and valence bands followed by exciton formation takes place in 17–30 ps depending on the excitation photon energy. The excitons formed at the band bottom are localized at thicker areas within a quantum well in 500 ps.     

Lattice damage in InGaN induced by swift heavy ion irradiation

The microstructural responses of In_0.32Ga_0.68N and In_0.9Ga_0.1N films to 2.25 GeV Xe ion irradiation have been investigated using x-ray diffraction, Raman scattering, ion channeling and transmission electron microscopy. It was found that the In-rich In_0.9Ga_0.1N is more susceptible to irradiation than the Ga-rich In_0.32Ga_0.68N. Xe ion irradiation with a fluence of 7× 10¹¹ ions·cm^-2 leads to little damage in In_0.32Ga_0.68N but an obvious lattice expansion in In_0.9Ga_0.1N. The level of lattice disorder in In_0.9Ga_0.1N increases after irradiation, due to the huge electronic energy deposition of the incident Xe ions. However, no Xe ion tracks were observed to be formed, which is attributed to the very high velocity of 2.25 GeV Xe ions. Point defects and/or small defect clusters are probably the dominant defect type in Xe-irradiated In_0.9Ga_0.1N.     

InxGa1-xAs/GaAs量子阱应变量对变温光致发光谱的影响

利用变温光致发光(PL)研究了In0.182Ga0.818As/GaAs应变及应变补偿量子阱在77～300 K温度范围内的发光特性.随着温度T的升高,PL峰位向低能方向移动.在应力作用下In0.182Ga0.818As/GaAs量子阱的价带顶轻空穴带和重空穴带发生了劈裂.通过理论计算推导应变随温度变化对InxGa1-x...     

Interband Stark effects in InxGa1−xAs/InyAl1−yAs coupled step quantum wells

The effects of an electric field on the interband transitions in In_xGa_1−xAs/In_yAl_1−yAs coupled step quantum wells have been investigated both experimentally and theoretically. A In_xGa_1−xAs/In_yAl_1−yAs coupled step quantum well sample consisted of the two sets of a 50 Å In_0.53Ga_0.47As shallow quantum well and a 50 Å In_0.65Ga_0.35As deep step quantum well bounded by two thick In_0.52Al_0.48As barriers separated by a 30 Å In_0.52Al_0.48As embedded potential barrier. The Stark shift of the interband transition energy in the In_xGa_1−xAs/In_yAl_1−yAs coupled step quantum well is larger than that of the single quantum well, and the oscillator strength in the In_xGa_1−xAs/In_yAl_1−yAs coupled step quantum well is larger than that in a coupled rectangular quantum well. These results indicate that In_xGa_1−xAs/In_yAl_1−yAs coupled step quantum wells hold promise for potential applications in optoelectron devices, such as tunable lasers.