Growing InAs/GaAs quantum dots by droplet epitaxy under MOVPE conditions

Technical Physics Letters - Results of studying the formation of InAs quantum dots (QDs) on GaAs(100) substrates by droplet epitaxy using trimethylindium and arsine (AsH3) as precursors are...     

Microstructure characterization of InAs0.93Sb0.07 films grown by ramp-cooled liquid phase epitaxy

InAs_0.93Sb_0.07 alloy thin films were grown by ramp-cooled liquid phase epitaxy on (100) InAs substrate using horizontally sliding multi-wells graphite boats. The systematic microstructural characterizations of the epi-grown films were analyzed by X-ray diffraction, scanning electronic microscopy and energy dispersive spectra. Four typical surface morphologies of the films were observed, which depend sensitively on growth parameters such as the growth temperature, the substrate etching time, the flux of the hydrogen, and the cooling range and rate. The film shows high crystal perfection with (100) orientation, as evidenced by X-ray measurement. The crystal quality of the epilayer was evaluated by the X-ray double axes diffraction, and the dislocation density was estimated through fitting the (200) and (400) rocking curves by Gaussian lineshape.     

Bismuth surfactant mediated growth of InAs quantum dots by molecular beam epitaxy

This paper explores the significance of using bismuth as a surfactant during the molecular beam epitaxy growth of InAs quantum dots (QDs). The results show that Bi-mediated growth provides a practical solution towards achieving lower density QDs with high optical quality. The InAs QDs grown using Bi as a surfactant exhibit a 50 % lower QD density, narrower QD size distribution, and a doubled photoluminescence peak intensity at 16 K compared to those grown without Bi.     

Photoluminescence study of low density InAs quantum clusters grown by molecular beam epitaxy

We report a systematic optical spectroscopy study of low density InAs quantum clusters (QCs) grown by molecular beam epitaxy. The photoluminescence (PL) spectra show emission features of a wetting layer (WL) which contains hybridized quantum well states. The low-energy tail of the QCs' PL profile is actually an ensemble of some sharp lines, originating from the emission of different exciton states (e.g. X, X*, XX*) in a single quasi-three-dimensional (Q3D) cluster as detailed in the micro-PL spectra. The temperature dependence of PL spectra indicates photocarrier distribution and transport in the QC-WL system. Furthermore, this small InAs Q3D cluster is integrated with a distributed Bragg reflector structure, and using optical excitation creates a single photon source with the second-order correlation function of g((2))(0) = 0.31 at 16 K.     

Enhanced radiative efficiency in GaN quantum dots grown by molecular beam epitaxy

Self-assembled GaN quantum dots (QDs), grown on AlN by molecular beam epitaxy, were investigated by time-resolved photoluminescence spectroscopy. We investigate the emission mechanism in GaN QDs by comparing the carrier recombination dynamics in single and multiple period QDs. At 100 K, the PL decay time in single period QD structures is considerably shorter than in stacked QDs. Compared to single period QDs, the room temperature PL efficiency is considerably enhanced in 20 period QDs due to the reduction in nonradiative recombination processes.     

Influence of growth parameters on the surface morphology and crystallinity of InSb epilayers grown by liquid phase epitaxy

Unintentionally doped homoepitaxial InSb films have been grown by liquid phase epitaxy employing ramp cooling and step cooling growth modes. The effect of growth temperature, degree of supercooling and growth duration on the surface morphology and crystallinity were investigated. The major surface features of the grown film like terracing, inclusions, meniscus lines, etc are presented step-by-step and a variety of methods devised to overcome such undesirable features are described in sufficient detail. The optimization of growth parameters have led to the growth of smooth and continuous films. From the detailed morphological, X-ray diffraction, scanning electron microscopic and Raman studies, a correlation between the surface morphology and crystallinity has been established.     

Self-organization of quantum dots in multilayer InAs/GaAs and InGaAs/GaAs structures by submonolayer migration-stimulated epitaxy

Multilayer structures of InGaAs/GaAs quantum dots fabricated by submonolayer migrationstimulated epitaxy have been studied experimentally by scanning tunneling microscopy and results are presented. These results clearly show that in multilayer structures, ordering of nanoobjects into rows occurs in InAs and InGaAs heteroepitaxial layers. Pis#x2019;ma Zh. Tekh. Fiz. 23, 80–84 (November 26, 1997)     

Microhardness of silicon layers grown by liquid phase epitaxy

The microhardness of silicon epilayers grown from Sn fluxes is found to be lower than that of the silicon substrates and to significantly depend on the crystallographic orientation of the substrates. The microhardness values follow a Gaussian distribution in all of the epilayers. Unintentional impurities are shown to have a significant effect on the microhardness of the epilayers. The addition of ytterbium to the high-temperature solution reduces the microhardness of the epilayers.     

Yb:CaF2 grown by liquid phase epitaxy

Ytterbium doped CaF₂ crystalline layers have been grown for the first time from high temperature solutions at controlled atmosphere by using the liquid phase epitaxy technique. Doped layers having thicknesses between a few microns to a hundred of microns have been grown onto non-oriented and (1 1 1) oriented CaF₂ substrates. The Yb³⁺:CaF₂ layers show structural properties very close to the undoped substrate without any further thermal treatment. Registration of room temperature emission spectra and fluorescence lifetime measurements performed with epitaxial layers corresponding to different ytterbium concentrations show similar spectroscopic properties as in the bulk crystals.     

Deep levels induced by InAs/GaAs quantum dots

Self-organised InAs/GaAs quantum dots (QDs) were formed by molecular beam epitaxy using the Stranski–Krastanov growth mode. Deep-level transient spectroscopy as well as secondary ion mass spectrometry have been used to characterise structures containing the QDs. DLTS depth profiling procedures indicate that deep level-related defects are localised in GaAs in the vicinity of the QD plane. For the first time, we report the presence of a deep level-related trap with an extremely high thermal activation energy of E_c − 1.03 eV. An electron trap at E_c − 0.78 eV can be identified as the well-known level related to the EL2 family. We conclude that a third trap revealed at E_c −0.57 eV is the familiar PL killer related to the intrinsic point defect-oxygen complex. The latter is confirmed by results of the SIMS study, which indicates that the amount of oxygen accumulated at the InAs/GaAs heterointerface is increased. This paper demonstrates that the EL2 and oxygen-related deep-level centers occur by the presence of InAs/GaAs QDs. We present the hypothesis that deep states could be a factor limiting the efficiency of QD-based devices.     

Simultaneous interface and interband lasing in InAs/InAsSbP heterostructures grown by metalorganic vapor phase epitaxy

Coherent radiation sources have been manufactured based on double heterostructures of the InAs/InAsSbP type grown by metalorganic vapor-phase epitaxy. The mode composition of the lasing spectrum is determined by simultaneous induced recombination at the heteroboundary and in the bulk of the active region, as well as nongenerated modes with intermediate frequencies. Additional optical losses at the intermediate modes decrease the slope of the laser intensity dependence on the current.     

Heterostructures with CdTe/ZnTe quantum dots for single photon emitters grown by molecular beam epitaxy

We report on the molecular beam epitaxy (MBE) of heterostructures with CdTe/ZnTe quantum dots (QDs) with relatively low surface density, which could be used as single-photon emitters. The QDs were formed on the surface of a 3.1- to 4.5-monolayer-thick two-dimensional strained CdTe layer by depositing amorphous Te layer and its fast thermal desorption. Subsequent thermal annealing of the surface with QDs in the absence of external Te flux led to strong broadening and short-wavelength shift of the QD photoluminescence (PL) peak. Measurement of the micro-PL spectra of individual CdTe/ZnTe quantum dots in fabricated mesastructures with a diameter of 200—1000 nm allowed estimation of the QD surface density as ~10¹⁰ cm^–2.     

Stress reduction and electric properties of InSb thin films grown by metalorganic vapor phase epitaxy on sapphire substrates with an InAs buffer layer

InSb thin films were grown by metalorganic vapor phase epitaxy using an InAs buffer layer on sapphire (0001) substrates. The stresses and strains in InSb were controlled by the thickness of the InAs buffer layer, and it was found that with decreasing compressive stress in InSb, the crystalline quality and the electrical properties improved. The thermoelectric properties of InSb were assessed and it was found that the power factor of InSb with a thickness of 5 μm reached as high as 5.8 × 10⁻³ W/mK² at 600 K.     

Photoconverters based on GaAs/Ge heterostructures grown by low-temperature liquid phase epitaxy

A low-temperature liquid phase epitaxy technique involving rapid cooling of a solution melt has been developed for the growth of epitaxial GaAs films on germanium substrates. Using this method, it is possible to obtain high-quality submicron GaAs epilayers on Ge substrates for photoelectric converters.     

HgCdTe/CdZnTe液相外延材料的倒易空间图研究

采用高分辨X射线衍射的例易空间图研究了HgCdTe／CdZnTe(-0．044％晶格失配)液相外延材料界面处品格结构，结果显示，通常使用的10μm厚的碲镉汞液相外延材料的晶格相对碲锌镉衬底已处于完全弛豫状态，并且外延层和衬底的品向发生了0．01。的偏离，但是，由于外延层中存在着组分梯度以及衬底和外延层热膨胀系数存在着差异，界面处外延层中仍存在着应力和应变。对称衍射和非对称衍射的实验结果均显示外延材料的例易空间图沿垂直于散射矢量方向有所扩展．这一结果表明晶格失配的弛豫使得界面处外延层的晶体结构呈镶嵌结构。实验也发现，外延层的非对称衍射倒易空间图的扩展偏离散射矢量方向，根据弛豫线模型，这也是由于界面处外延层存在组分梯度和应变梯度所造成的。     

Transformation of InAs islands to quantum ring structures by metalorganic vapor phase epitaxy

The transformation of InAs islands to quantum rings (QRs) by metalorganic vapor phase epitaxy is investigated. After covering the InAs islands with a thin GaAs partial capping layer and annealing under tertiarybutylarsine (TBAs) flow, ring-shaped nanostructures with a density of 10(7)-10(9)?cm(-2) are obtained at 500-600?°C. The effects of the growth temperature, annealing process and thickness of the partial capping layer are studied. Optimum values for the annealing time and the partial capping layer thickness were found to be 60-120?s and 0.5-2.0?nm, respectively. Low temperature photoluminescence (PL) emission peaks from islands and QRs grown at 500?°C are observed at 1.04?eV and 1.22?eV, respectively. The annealing temperature affected the QR evolution and the PL emission from the QRs due to the temperature dependence of the diffusion rate of indium atoms.     

Effect of thin intermediate-layer of InAs quantum dots on the physical properties of InSb films grown on (001) GaAs

In this study the formation of a semiconducting InSb layer, preceded by the growth of an intermediate layer of InAs quantum dots, is attempted on (001) GaAs substrate. From the analysis of atomic-force-microscopy and transmission-electron-microscopy images together with Raman spectra of the InSb films, it is found that there exists a particular layer-thickness of ~ 0.5 μm above which the structural and transport qualities of the film are considerably enhanced. The resultant 2.60-μm-thick InSb layer, grown at the substrate temperature of 400 °C and under the Sb flux of 1.5 × 10^− 6 Torr, shows the electron mobility as high as 67,890 cm²/Vs.     

Enhancement of optical properties of InAs quantum dots grown by using periodic arsine interruption

We investigated the morphological and optical properties of InAs quantum dots (QDs) grown by using periodic arsine interruption (PAI) and compared them with QDs grown conventionally. In the conventional growth, the formation of large islands was observed, which suppresses the nucleation and growth of QDs. Furthermore, the growth of capping layers was significantly degraded by these large islands. On the other hand, in the PAI growth, the formation of large islands was completely suppressed, resulting in the increase of the density and aspect ratio of QDs and the uniform growth of capping layers. As a result of photoluminescence (PL) measurements, we found that the emission efficiency was enhanced and the full-width-half-maximum was reduced to 32 meV. The temperature dependence of these optical properties also revealed the enhancement of the uniformity of QDs grown by the PAI method.