Formation and crystal structure of GaSb/GaP quantum dots

The atomic structure of GaSb/GaP quantum dots grown via molecular beam epitaxy on a (100) GaP surface at epitaxy temperatures of 420–470°C is investigated. It is established that, depending on morphology of the GaP growth surface, the deposition of 1 ML of GaSb leads to the formation of strained Ga(Sb, P)/GaP or fully relaxed GaSb/GaP quantum dots. The obtained heterostructures exhibit high photoluminescence efficiency.     

Optimization of growth parameters for MOVPE-grown GaSb and Ga1−xInxSb

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520 °C at atmospheric pressure. Trimethylindium was added in the case of Ga_1−xIn_xSb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga_1−xIn_xSb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga_1−xIn_xSb vapour composition and solid composition has been studied at a V/III ratio of 0.78.     

Growth of gallium nitride epitaxial layers and applications

The lack of appropriate substrates has delayed the realisation of devices based on IIInitrides. Currently, the heteroepitaxial growth of GaN by metal organic vapour phase epitaxy (MOVPE) produces GaN layers which, despite huge densities of dislocations, allow the fabrication of highly efficient optoelectronic devices. Henceforth, a new technology in heteroepitaxy of GaN, the epitaxial lateral overgrowth (ELO) has produced GaN layers in which the density of dislocations has been reduced by several orders of magnitude. With the ELO, nitride based laser diodes (LDs) working at room temperature in cw mode with a lifetime of 10,000 hours have been demonstrated by Nichia. In addition to LDs, IIInitrides presently offer a wide range of applications in optoelectronics (high brightness light emitting diodes (LEDs), from amber to UV, solar blind detectors); in electronics, high temperature/high power field effect transistors (FETs). The development of molecular beam epitaxy (MBE) of nitrides has been hindered during several years by the lack of an efficient nitrogen source. This problem being solved, MBE has recently demonstrated state-of-theart quantum well and quantum dot heterostructures, and 2D electron gas heterostructures.     

Growth of strain-compensated InGaAs/GaAsP multiple quantum wells by MOVPE

InGaAs/GaAsP strain-compensated multiple quantum wells (SCMQWs) and strained InGaAs/GaAsmultiple quantum wells (MQWs) were grown on GaAs substrates by metal organic vapor phase epitaxy(MOVPE). The results of double crystal X-ray diffraction (DCXRD) revealed that strain relief had beenpartly accommodated by the misfit dislocation formation in the strained MQW material. It led to thatthe full width half maximums (FWHMs) of superlattice satellite peaks are broader than those of SCMQWstructures, and there was no detectable room temperature photoluminecence(RT-PL)for the strained     

Scanning tunneling microscopy of InAs/GaSb superlattices with various growth conditions

Cross-sectional scanning tunneling microscopy (STM) is used to characterize InAs/GaSb superlattices, grown by molecular beam epitaxy (MBE). Previous STM studies have found an interface asymmetry, with the interfaces of InAs grown on GaSb being rougher than those of GaSb on InAs. In the present work, a comparison is made between samples grown under various conditions, using elevated growth temperature or using atomic layer epitaxy (ALE). In both cases, the interface asymmetry is found to decrease compared to MBE growth at 380°C. In addition, Sb incorporation in the InAs layers is observed directly in the STM images. It is argued that the additional roughness seen at the InAs on GaSb interfaces arises in part from incorporation of excess Sb into the growing InAs layers. Elevated temperatures reduces this incorporation, and hence produces smoother interfaces.     

Ultrathin InAs and modulated InGaAs layers in GaAs grown by MOVPE studied by photomodulated reflectance spectroscopy

Photomodulated reflectance spectroscopy (PR) and X-ray diffraction (XRD) were used for the characterization of highly strained ultrathin InAs quantum wells and modulated InGaAs layers in GaAs grown by metal-organic vapor phase epitaxy (MOVPE). Structures were grown in AIXTRON 200 reactor at 500 °C on (1 0 0) oriented GaAs substrates by sequential growth of InAs and GaAs layers. Various PR spectral features corresponding to optical transitions between ground and excited states in the layers were identified by means of simulation of electronic states in these structures using nextnano³ quantum simulator. Different models of InAs layer growth were used to explain both the XRD and PR data. Results show that the Gaussian distribution of In atoms within few monolayers gives the best fit for our MOVPE grown ultrathin InAs layers.     

Photoluminescence and secondary ion mass spectroscopy characterization of GaAs-AlGaAs quantum wells grown on GaAs (1 0 0) substrates with different surface treatments

GaAs (1 0 0) substrates prepared in a quartz chamber under a H₂/As₄ flux, and then exposed to air were used for the subsequent growth of GaAs-AlGaAs single quantum wells by molecular beam epitaxy. The substrates prepared by this method showed atomically flat surfaces corroborated by atomic force microscopy analysis. Quantum wells grown directly on these substrates without a GaAs buffer layer exhibited narrow and intense photoluminescence peaks, an indication of a high quality material. The secondary ion mass spectroscopy analysis showed oxygen and carbon traces on the first AlGaAs barrier layer grown after air exposure with no effects on the quantum wells optical emissions. From the results we conclude that the prepared GaAs surfaces are useful for the epitaxial growth of high quality quantum structures.     

GaAs surface passivation by ultra-thin epitaxial GaP layer and surface As-P exchange

The GaAs surface passivation effects of epitaxially grown ultra-thin GaP layers and surface As-P exchange have been investigated. Optical properties of passivated and unpassivated InGaAs/GaAs near-surface quantum wells (QWs) grown by metal organic vapor phase epitaxy (MOVPE) are studied by low-temperature continuous-wave and time-resolved photoluminescence (PL). By optimizing the growth conditions, smooth surface morphologies and significant improvement of optical properties were observed for both passivation methods. Passivation improved the PL intensity more than two orders of magnitude and notably increased the PL decay time.     

Orientation-patterned templates GaAs/Ge/GaAs for nonlinear optical devices. I. Molecular beam epitaxy

GaAs/Ge/GaAs heterostructures in which the GaAs layer lattice on Ge is rotated at a right angle to the substrate plane are grown by molecular-beam epitaxy (MBE). Such heterostructures are grown in different epitaxial setups for GaAs and for Ge with wafer transfer through air tor the first time. It is proposed to use surfactants (Bi, Sb) to control GaAs layer nucleation on Ge.     

Nanoscale ZnCdS/ZnSSe heterostructures for semiconductor lasers

We investigated cathode luminescence of ZnCdS/ZnSSe heterostructures and structures with quantum wells (QW) grown by vapor phase epitaxy from metalloorganic compounds depending on the excitation level, composition, and thickness of the ZnCdS layer. The observed dependences are explained by specific features of the energy band diagram of heterostructures with gaps in type II bands and composition nonuniformity over the ZnCdS layer thickness. A 478-nm laser with transverse optical pumping by N₂-laser was realized at T = 80 K on the ZnCdS/ZnS/ZnSSe structure with QW.     

Examination of the Capabilities of Metalorganic Vapor-Phase Epitaxy in Fabrication of Thin InAs/GaSb Layers

Technical Physics - The capabilities of metalorganic vapor-phase epitaxy (MOVPE) in fabrication of structures with thin (1–2 nm) alternating InAs/GaSb layers on a GaSb substrate are studied....     

GaSb/AlSb/GaAs应变层结构的分子束外延生长

本文以反射式高能电子衍射(RHEED)和其强度振荡为监测手段,在半绝缘GaAs衬底上成功地生长GaSb/AlSb/GaAs应变层结构,RHEED图样表明,GaSb正常生长时为Sb稳定的C(2×6)结构,AlSb为稳定的(1×3)结构,作者观察并记录GaSb,AlSb生长时的RHEED强度振荡,并利用它成功地生长10个周期的GaSb/AlSb超晶格,透射电子显微镜照片显示界面平整、清晰,采用较厚的AlSb过渡层及适当的生长条件,可在半绝缘GaAs衬底上生长出质量好的GaSb外延层,其X射线双晶衍射半峰宽小于 关键词：     

Antimonide-based lasers and DFB laser diodes in the 2–2.7 μm wavelength range for absorption spectroscopy

We report on Fabry–Pérot semiconductor lasers and single frequency distributed feedback lasers based on GaInAsSb/AlGaAsSb quantum wells. The laser structures were grown by molecular beam epitaxy on GaSb substrates. The devices were etched either by wet process or by inductively coupled plasma (ICP) process. Electron-beam lithography was used to deposit a metal Bragg grating on each side of the laser ridge to fabricate the DFB lasers. The devices all operate in the continuous wave regime at room temperature with a single frequency emission above 2.6 μm and good tuning properties, making them well adapted to tunable diode laser absorption spectroscopy. PACS 42.55.Px; 42.62.Fi     

Formation and atomic structure of GaSb nanostructures in GaAs studied by cross-sectional scanning tunneling microscopy

GaSb nanostructures in GaAs, grown by metalorganic chemical vapor deposition, were studied with cross-sectional scanning tunneling microscopy. Three different samples were examined, containing a thin quantum well, a quantum well near the critical thickness for dot formation, and finally self-organized quantum dots with base lengths of 5–8 nm and heights of about 2 nm. The dots are intermixed with a GaSb content between 60% and 100%. Also small 3D and 2D islands were observed, possibly representing quantum dots in an early growth stage and quantum dot precursors. All GaSb layers exhibit gaps, which are indications of an island-like growth mode during epitaxy.     

InSb/InAsSb nanostructures for Mid-IR optoelectronics

The technique of preparation of nanostructures with InSb quantum dots in an InAs(Sb) matrix, emitting in the mid-IR range upon optical and injection pumping, by molecular beam epitaxy is considered and the structural and optical properties of these nanostructures are investigated. The characteristics of the first injection lasers based on III–V/II–VI hybrid heterostructures with InSb/InAs(Sb) quantum dots in the active region are reported.     

Infrared photomodulation spectroscopy of an In 0.22Ga 0.78Sb/GaSb single quantum well

Photoreflectance and phototransmittance have been used for the investigation of optical transitions in an In _0.22Ga _0.78Sb/GaSb single quantum well grown by molecular beam epitaxy on a GaSb substrate. High sensitivity of these photomodulation techniques has allowed the observation of excited state transitions including parity forbidden ones, in contrast to standard spectroscopic methods which usually probe only the fundamental transition. The transition energies have been calculated using the envelope function approach and taking into account strains and excitonic effects. Evidence of the great advantage of modulation spectroscopy in the infrared region (1.5–1.8 μ m) in comparison to standard photoluminescence, reflectivity and transmission coefficient measurements has been shown.     

Type II GaSb/GaAs quantum dot/ring stacks with extended photoresponse for efficient solar cells

We report on the fabrication of GaAs based p–i–n solar cells containing 5 and 10 layers of type II GaSb quantum rings grown by molecular beam epitaxy. Solar cells containing quantum rings show improved efficiency at longer wavelengths into the near-IR extending up to 1500 nm and show enhanced short-circuit current under 1 sun illumination compared to a GaAs control cell. A reduction in the open-circuit voltage is observed due to the build-up of internal strain. The MBE growth, formation and photoluminescence of single and stacked layers of GaSb/GaAs quantum rings are also presented.     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

GaInSb/GaSb量子阱结构的低温光致发光谱

ＧａＩｎＳｂ三元合金半导体可用于制作工作于１．５５～５．５μｍ波段范围的光电子器件．在光通讯方面,需要２．５５μｍ波长的激光器和接收器,ＧａＩｎＳｂ半导体合金无疑是一种可选的材料．此外,这种材料也可用于制作高速电子器件,与ＧａＡｓ基异质结构相比,Ｇａ...     

Observation of ultra-broadband terahertz emission from ZnTe films grown by metaloganic vapor epitaxy

ZnTe films were grown on (0001) sapphire substrates by the metalorganic vapor phase epitaxy (MOVPE) method. Single crystalline (111) ZnTe epitaxial layers were confirmed by x-ray diffraction, reflection high-energy electron diffraction, and cathodoluminescence measurements. Emission of THz radiation with a spectral distribution up to 40 THz was clearly observed from the ZnTe film with a thickness of 10 μm. The results show that MOVPE is a promising growth method for obtaining high-quality ZnTe epitaxial films on sapphire substrates, which paves the way for obtaining thinner ZnTe films to provide a flatter frequency response in THz device applications.