Stability of interfaces in pseudomorphic ingaas hemts

Considerable progress is now reported on pseudomorphic InGaAs high mobility transistors (PM. HEMTs). However, structures which exhibit the best performances are thermodynamically metastable. The stabilities of commercially available devices have been studied. Investigations of both GaAs InGaAs and AlGaAs/InGaAs interface vicinities have been performed through deep level characterizations. Life-testing experiments have then been carried out in order to assess the stability of the InGaAs buried strained layer and related interfaces during operation. Deep level studies together with electrical parameter measurements indicate that interfaces of InGaAs strained quantum well HEMTs do not induce particular degradations after 3000 hours into biased ageing tests.     

Effect of stress on interface transformation in thin semiconducting layers

The effect of high pressure (1.2 GPa)–high temperature (up to 1400 K) treatment (HP-HT) on the structural properties of GaMnAs/GaAs, AlGaAs/GaAs and Si/SiO₂/Si (SOI) structures was studied by high resolution X-ray diffractometry. GaMnAs layers remain strained after the HP-HT treatment, while it results in anisotropic strain relaxation of AlGaAs. The change in lattice parameters of A(III)B(V) layers is explained as an effect of relaxation of the misfit strain via creation of misfit dislocations and of other extended defects, as well as by diffusion of Mn or Al to dislocations. The treatment of SOI structures resulted in increased (as compared to the effect of annealing at 10⁵ Pa) strain between the Si top layer and the Si bulk.     

Single-crystalline GaAs, AlGaAs, and InGaAs layers grown by metalorganic VPE on porous GaAs substrates

Conditions for the growth of single-crystalline GaAs, AlGaAs, and InGaAs layers by metalorganic VPE were established and the corresponding semiconductor films were obtained on porous GaAs substrates. Comparative data on the morphology, structure, and electrical homogeneity of the epitaxial layers grown on the porous and monolithic substrates are presented. It was found that passage to the porous substrates leads to changes in the film growth rate and morphology, the concentration of electrically active defects, and their distribution in depth of the epitaxial structures.     

A hydrogen-sensitive structure based on semi-insulating gallium arsenide

The response characteristics of a simple hydrogen-sensitive structure based on semi-insulating single crystal gallium arsenide with planar palladium electrodes deposited onto the oxidized substrate surface are studied. It is demonstrated that such structures exhibit a fast response to hydrogen present in the gas phase. The sensitivity can be increased by growing, prior to the electrode formation, an intermediate epitaxial GaAs film with built-in strained quantum-confined layers of InGaAs and InAs onto the semi-insulating GaAs substrate.     

The effects of ionizing radiation on GaAs/AlGaAs and InGaAs/AlInAs heterojunction bipolar transistors

GaAs/AlGaAs and InGaAs/AlInAs Heterojunction Bipolar Transistors (HBTs) have been exposed to ⁶⁰Co γ-ray doses up to 100 MRad. The d.c. current gain of GaAs/AlGaAs devices showed small increases for doses up to 75 MRad, due to a faster decrease in base current relative to collector current. After 100 MRad, none of the original devices were operational because of failure of the base-collector contact metallization (TiPtAu). Devices with either Be- or C-doped base layers showed the same response to the γ-ray doses. The InGaAs/AlInAs HBTs showed a small decrease (<10%) in current gain after a total dose of 88 MRad and appear to be somewhat more resistant to damage from accumulated doses of radiation than comparable GaAs devices. GaAs/AlGaAs devices exposed to transient (120 nsec) pulses of high energy electrons show rapid recovery of both collector and base currents, with no long transient responses observed. Numerical simulations of the recovery of both GaAs- and InP-based HBTs after transient doses of ionizing radiation suggest that both are relatively immune to damage up to dose rates of 10¹¹ Rad s⁻¹ with faster recovery of the GaAs devices because of the shorter recombination times in this material.     

AlxGa−xAs/GaAs heterostructure characterization by wet chemical etching

Selective wet chemical etching of the Al_xGa_1−xAs/GaAs system has been applied to heterostructure characterization. Samples of LPE grown AlGaAs/GaAs laser double-heterostructures and separate confinement heterostructures as well as antiresonant reflecting optical waveguides heterostructures were treated with “I2 solution” (I₂:KI:H₂O) and hydrochloric acid. These compounds selectively etch the ternary Al_xGa_1−xAs layers, but with different “threshold composition” x_th values (the x value is that above which the etching rate of a given compound increases sharply). Selectively etched samples have been examined by SEM. The experimental dependence of etching rate on the x value for I2 solution has been derived. From this dependence, the x composition of any ternary layer can be estimated simply. Observations were made of the “microscopic” properties of the heterostructure, such as the smoothness of the interfaces and the uniformity of layers. All imperfections resulting from the growth process, such as interface perturbations or compositional nonuniformity of layers, are clearly seen. An additional advantage of this etching technique is its simplicity. It allows quick examination of grown heterostructure for the selection of wafers for further processing.     

Shape control of InGaAs nanostructures on nominal GaAs(001): dashes and dots

A method for fabricating self-assembled InGaAs quantum dashes on a nominal GaAs(001) substrate is presented. InGaAs layers were grown on nominal GaAs(001) substrates at a low temperature to suppress the Stranski-Krastanov transition as well as indium segregation and indium desorption, then annealed at high temperatures to induce self-assembly. While typical direct growth at the annealing temperature has yielded only quantum dot shapes, our approach has enabled us to control the shape of self-assembled nanostructures from quantum dashes to quantum dots and eventually quantum dot-chains. The major factor controlling the shape of InGaAs nanostructures was found to be the thickness of the pseudomorphic In(0.4)Ga(0.6)As layer.     

XPS定量测量三元合金ZnS1-xTex薄膜组分x的研究

利用XPS定量测量分子束外延生长的三元合金碲硫锌ZnS1-xTex(0 相似文献   

In situ optical monitoring of layer composition in the chemical beam epitaxy of AlGaAs from amine-alane sources

Normal incidence in situ laser reflectometry (LR) was used to give reliable quantitative composition and thickness information during epitaxial growth of GaAs, AlGaAs, and AlAs by chemical beam epitaxy. AlGaAs layers grown using amine-alane sources showed variations in growth rate and composition arising from instabilities in the source. In the case of dimethylethylamine-alane, the growth rate varied from run to run, between layers in a multilayer structure and during the growth of thick AlGaAs layers. The use of LR gave a rapid indication of the problem, which was solved by using trimethylamine-alane as a source.     

Effect of a modified cover layer on the properties of hydrogen-sensitive Pd/GaAs/InGaAs diode heterostructures with quantum wells

The influence of a developed surface relief of an overgrowth (cover) layer modified by anodic oxidation and/or etching on the characteristics of hydrogen-sensitive Pd/GaAs/InGaAs diode heterostructures with quantum wells has been studied. The modified structures exhibit a significant increase in sensitivity and response speed, which is related for the most part to a decrease in the effective distance from the surface, on which atomic hydrogen is chemisorbed, to an elastically strained layer of the InGaAs quantum well. This layer retards the diffusion of hydrogen, which leads to an increase in the hydrogen concentration at the interface.     

The effect of helium ion implantation on the relaxation of strained InGaAs thin films

Previous work on pseudomorphic SiGe on Si has shown that a significant reduction in the threading dislocation density can be achieved through appropriate ion beam processing. Helium ion implantation was used in an analogous study to induce strain relaxation within strained pseudomorphic InGaAs layers on GaAs through the intentional introduction of subsurface damage without the introduction of surface nucleated dislocations and their associated threading segments. Wafers of fully-strained 28 nm thick films of In_0.24Ga_0.76As were separately implanted with helium doses of 5 × 10¹⁴, 2 × 10¹⁵, and 1 × 10¹⁶ cm⁻² at 25 keV. These wafers became substrates for additional InGaAs film growth. The final InGaAs films always exhibited lower residual strain as compared to films grown directly on a control substrate of non-implanted GaAs. The broadening of the X-ray peaks indicates an increase in dislocation density within the InGaAs films and the strain relaxation was found to occur with a significant increase in surface roughness. This result stands in contrast to related work on SiGe films on Si where a reduction of the threading dislocation density within a SiGe film was observed. The reaction of the InGaAs/GaAs structure and materials to ion irradiation, with local disturbance to the stoichiometry, could preclude the use of ion beam techniques for realizing a reduction in threading dislocation density during strain relaxation.     

Reliability and degradation of 980 NM InGaAs/GaAs strained quantum well lasers

Degradation behaviours of 980 nm InGaAs/GaAs strained quantum well (QW) lasers are clarified and compared with normal AlGaAdGaAs, InGaAsP/InP and GaAs/GaAs QW lasers. Through various ageing tests, it is confirmed that 980 nm InGaAs/GaAs strained QW lasers are applicable to optical fibre transmission systems where the components are required to be highly reliable.     

光阴极材料GaAs/AlGaAs的组分分析

为探索砷化镓光阴极的光电灵敏度的影响因素 ,利用X射线光电子能谱、二次离子质谱和电化学方法测试和分析了国内和国外GaAs光阴极材料GaAs/AlGaAs的C ,O含量和空穴浓度分布。实验发现 ,国内的材料在GaAs/AlGaAs界面及AlGaAs层的O含量分别为 7 6 %和 10 6 % ,C浓度分别为 5 2×10 18atoms/cm3和 1 0× 10 19atoms/cm3,而国外的材料的O含量相应为 1 0 %和 1 5%。国内的材料GaAs和AlGaAs层的空穴浓度分别为 7× 10 18～ 4× 10 19cm- 3和 8× 10 17cm- 3,而国外材料的相应值分别为 (1 8～ 2 0 )× 10 19cm- 3和 5× 10 18cm- 3。分析认为 ,层中及界面的C ,O杂质偏高和空穴浓度分布不尽合理使光电子扩散长度减小 ,后界面复合增大 ,导致了光电灵敏度下降。     

Optical-constant calculation of non-uniform thickness thin films of the Ge10As15Se75 chalcogenide glassy alloy in the sub-band-gap region (0.1–1.8 eV)

Optical-transmission spectra are very sensitive to inhomogeneities in thin films. In particular, a non-uniform thickness produces a clear shrinking in the transmission spectrum at normal incidence. If this deformation is not taken into account, it may lead to serious errors in the calculated values of the refractive index and film thickness. In this paper, a method first applied by Swanepoel for enabling the transformation of an optical-transmission spectrum of a thin film of wedge-shaped thickness into the spectrum of a uniform film, whose thickness is equal to the average thickness of the non-uniform layer, has been employed. This leads subsequently to the accurate derivation of the refractive index in the subgap region (0.1–1.8 eV), the average thickness, as well as a parameter indicating the degree of film-thickness uniformity. This optical procedure is applied to the particular case of freshly-prepared films of the Ge₁₀As₁₅Se₇₅ ternary chalcogenide glassy alloy. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-oscillator model. The optical-absorption edge is described using the ‘non-direct transition' model proposed by Tauc, and the optical energy gap is calculated by Tauc's extrapolation. Finally, the photo-induced and thermally induced changes in the optical properties of the a-Ge₁₀As₁₅Se₇₅ layers are also studied.     

Preparation of thin GaAs suspended membranes for gas micro-sensors using plasma etching

The GaAs/AlGaAs heterostructure layer system grown by MBE on GaAs substrate was designed to be used for micro-mechanical structure fabrication. In the first step, double-side aligned photolithography is carried out to define the etching masks on both sides of the substrate. After this, highly selective reactive ion etching (SRIE) of GaAs from the front side is used to determine the lateral dimensions of the membrane structure. The vertical dimension is defined by deep backside SRIE through a 300 μm thick GaAs substrate to the AlGaAs etch stop layer, hence the structure thickness is precisely determined by the thickness of MBE-grown GaAs layer over this etch stop layer. The last step is selective etching of the AlGaAs etch stop layer. The thermal resistance value of the membrane structure as high as 21 K/mW is achieved.     

Theoretical study on controllability of quantum state energy in an InGaAs/GaAs quantum dot buried in InGaAs

We theoretically studied the relationship between quantum energy states and structural parameters of an InGaAs/GaAs quantum dot (QD) buried in strained InGaAs, emitting at 1.1 to 1.4 em. The crystal distortion of the buried QD structure in three dimensions was computed based on the three-dimensional finite element method. Under the computed strain fields, the Schr?dinger equation was solved to obtain wavefunctions and eigenenergies. By calculating the dependence on structural parameters, we investigated the controllable range of the ground state energy and the energy separation between the ground state and the first excited state. We found that the energy separation exhibited a maximum value as a function of QD composition, enabling us to identify the composition of the QD structure. The effects of the burying layer composition and QD diameter were also investigated to expand the controllable range of the state energy. We also showed that the wavefunction symmetry was improved by burying the QD in the InGaAs layer. Our results will be useful in developing advanced devices for optical telecommunications and quantum information technology.     

941nm连续波高功率半导体激光器线阵列

用金属有机化合物气相淀积(MOCVD)技术生长了InGaAs／GaAs／AlGaAs分别限制应变单量子阱激光器材料。利用该材料制成了半导体激光器线阵列,连续波工作条件下的中心激射波长为940．5nm,输出功率高达37．7W(45A、2．0V),斜率效率可达0．99W／A(外微分量子效率为75％),最高转换效率超过45％,阈值电流密度为117A／cm^2,该波长的半导体激光器是Yb：YAG固体激光器的理想泵浦源。     

Investigation of amorphous Ni0.60Nb0.40 diffusion barriers

Interactions of Ni_0.60Nb_0.40 amorphous alloys with polycrystalline overlayers of gold and copper and single-crystal substrates of silicon. GaAs and GaP were observed with Auger depth profiling. The Ni-Nb layer was deposited by r.f. sputtering and was approximately 5000 Å thick. The overlayers were evaporated to a thickness of 1000 Å. The amorphous metal reacted with the gold overlayers and the GaAs and GaP substrates at temperatures well below the nominal crystallization temperature of 650 °C. The Cu/Ni-Nb/Si system, in contrast, was stable at 600 °C for at least 1 h. Samples were also measured that had been contaminated with approximately 5–10 at.% O. Complete separation of the niobium and nickel into distinct layers was seen. For the samples on silicon substrates this separation was accompanied by the formation of a nickel silicide layer.     

Emission wavelength trimming of self-assembled InGaAs/GaAs quantum dots with GaAs/AlGaAs superlattices by rapid thermal annealing

The effects of rapid thermal annealing on InGaAs quantum dots grown by atomic layer molecular beam epitaxy to the structural transformation and optical properties are investigated. No misfit dislocation was observed from either the as-grown or annealed dots. The size and composition of the quantum dots become more uniform upon annealing mainly from the height fluctuation as predicted by the theoretical model. Large bandgap blue shifts, resulted from the In and Ga interdiffusion, were observed with the preservation of three-dimensional carrier confinement. The GaAs/AlGaAs superlattice was found to minimize the defect diffusion and dot interdiffusion during the high-temperature epitaxial overgrowth.     

Carbon doped GaAs and AlGaAs grown by OMVPE: doping properties, oxygen incorporation, and hydrogen passivation

The carbon-doping behavior of GaAs and AlGaAs grown by organometallic vapor phase epitaxy was examined using AsH₃ or tertiarybutylarisine (TBAs) as the arsenic precursors. Carbon tetrachloride was utilized as the carbon dopant precursor for GaAs and AlGaAs. In addition, the intrinsic carbon doping of AlGaAs was also examined for these two As sources. The use of TBAs led to a significant reduction in carbon incorporation, by approximately a factor of 5–10 per mole of As precursor, both with respect to extrinsic and intrinsic carbon incorporation. For the GaAs:C layers grown at temperatures 550°C, significant concentrations (10−6 × 10¹⁹ cm⁻³) of hydrogen were detected. Approximately 25–55% of the carbon acceptors were passivated by the hydrogen, based on Hall measurements and infrared absorption measurements. The CCl₄ source introduced oxygen into the AlGaAs layers. TBAs was more effective in reducing oxygen incorporation compared to AsH₃ and the concentration of oxygen was reduced with either increasing TBAs or AsH₃ flow rate.