Linear electrooptic coefficient of InP nanowires

A novel fabrication procedure is developed that allows for the direct measurement of the linear electrooptic coefficient of semiconducting nanowires to determine their viability for use in electrooptic devices. Vertically aligned InP nanowires are transferred from their growth substrate to a glass substrate using a host polymer, while still retaining the alignment of the nanowires. The linear electrooptic coefficient of the InP nanowires exhibited a 1-2 orders of magnitude enhancement over bulk InP and ranged from 31 to 147 pm/V. The figure of merit, n3r, exhibited a factor of 20 enhancement over lithium niobate and ranged from 1010 to 4817 pm/V.     

张应变GaAs层引入使InAs/InP量子点有序化排列的机理研究

采用ＬＰ－ＭＯＶＰＥ技术,在（００１）ＩｎＰ衬底上生长的ＩｎＡｓ／ＩｎＰ自组装量子点是无序的。为了解决这个问题,在ＩｎＰ衬底上先生长张应变的ＧａＡｓ层,然后再生长ＩｎＡｓ层,可得到有序化排列的量子点。本文对张应变ＧａＡｓ层引入使量子点有序化排列的机理进行了分析,为生长有序化、高密度,均匀性好自组装量子点提供了依据。     

Wurtzite InP/InAs/InP core-shell nanowires emitting at telecommunication wavelengths on Si substrate

Optical properties of wurtzite InP/InAs/InP core-shell nanowires grown on silicon substrates by solid source molecular beam epitaxy are studied by means of photoluminescence and microphotoluminescence. The growth conditions were optimized to obtain purely wurtzite radial quantum wells emitting in the telecom bands with a radiative lifetime in the 5-7 ns range at 14 K. Optical studies on single nanowires reveal that the polarization is mainly parallel to the growth direction. A 20-fold reduction of the photoluminescence intensity is observed between 14 and 300 K confirming the very good quality of the nanowires.     

VLS growth of alternating InAsP/InP heterostructure nanowires for multiple-quantum-dot structures

We investigated the Au-assisted growth of alternating InAsP/InP heterostructures in wurtzite InP nanowires on InP(111)B substrates for constructing multiple-quantum-dot structures. Vertical InP nanowires without stacking faults were obtained at a high PH(3)/TMIn mole flow ratio of 300-1000. We found that the growth rate changed largely when approximately 40 min passed. Ten InAsP layers were inserted in the InP nanowire, and it was found that both the InP growth rate and the background As level increased after the As supply. We also grew the same structure using TBAs/TBP and could reduce the As level in the InP segments. A simulation using a finite-difference time-domain method suggests that the nanowire growth was dominated by the diffusion of the reaction species with long residence time on the surface. For TBAs/TBP, when the source gases were changed, the formed surface species showed a short diffusion length so as to reduce the As background after the InAsP growth.     

Threshold Fluence Measurement for Laser Liftoff of InP Thin Films by Selective Absorption

We explore conditions for achieving laser liftoff in epitaxially grown heterojunctions, in which single crystal thin films can be separated from their growth substrates using a selectively absorbing buried intermediate layer. Because this highly non‐linear process is subject to a variety of process instabilities, it is essential to accurately characterize the parameters resulting in liftoff. Here, we present an InP/InGaAs/InP heterojunction as a model system for such characterization. We show separation of InP thin films from single crystal InP growth substrates, wherein a ≈10 ns, Nd:YAG laser pulse selectively heats a coherently strained, buried InGaAs layer. We develop a technique to measure liftoff threshold fluences within an inhomogeneous laser spatial profile, and apply this technique to determine threshold fluences of the order 0.5 J cm^?2 for our specimens. We find that the fluence at the InGaAs layer is limited by non‐linear absorption and InP surface damage at high powers, and measure the energy transmission in an InP substrate from 0 to 8 J cm^?2. Characterization of the ejected thin films shows crack‐free, single crystal InP. Finally, we present evidence that the hot InGaAs initiates a liquid phase front that travels into the InP substrate during liftoff.

     

Growth of polycrystalline InP thin films by the pulsed laser deposition technique

The growth of polycrystalline InP films on glass substrates by the pulsed laser deposition technique is reported. Optimal growth conditions as high vacuum and relatively low substrate temperature were necessary to obtain stoichiometric InP layers. Structural and morphological characterizations of the samples are shown. X-ray diffraction shows that the stoichiometric InP films were face-centered cubic with preferred orientation of the crystallites over the (111) plane and mean grain size of about 60 nm. We also discuss the consequences of adverse growth conditions as bad vacuum and high substrate temperature on the film stoichiometry.     

Native-oxide-based selective area growth of InP nanowires via metal-organic molecular beam epitaxy mediated by surface diffusion

The growth of InP nanowires on an InP(111) B substrate is reported. The substrate native oxide was not removed from the surface prior to growth. Nanowires were grown at 400 °C from gold catalysts in a selective area manner, without bulk growth. Unlike SiO(2)-based metal-organic molecular beam epitaxy selective area growth, the growth reported here is mediated by surface diffusion with a characteristic diffusion length of 4 μm, about an order of magnitude larger than values for diffusion on bare substrates. A pre-growth heating treatment at 450 °C was found to increase the yield of nanowire nucleation from the gold catalysts.     

Growth of InAs/InP core-shell nanowires with various pure crystal structures

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (～500?°C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460?°C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.     

A high-coverage nanoparticle monolayer for the fabrication of a subwavelength structure on InP substrates

Subwavelength structures (SWSs) were fabricated on the Indium Phosphide (InP) substrate by utilizing the confined convective self-assembly (CCSA) method followed by reactive ion etching (RIE). The surface condition of the InP substrate was changed by depositing a 30-nm-thick SiO2 layer and subsequently treating the surface with O2 plasma to achieve better surface coverage. The surface coverage of nanoparticle monolayer reached 90% by using O2 plasma-treated SiO2/InP substrate among three kinds of starting substrates such as the bare InP, SiO2/InP and O2 plasma-treated SiO2/InP substrate. A nanoparticle monolayer consisting of polystyrene spheres with diameter of 300 nm was used as an etch mask for transferring a two-dimensional periodic pattern onto the InP substrate. The fabricated conical SWS with an aspect ratio of 1.25 on the O2 plasma-treated SiO2/InP substrate exhibited the lowest reflectance. The average reflectance of the conical SWS was 5.84% in a spectral range between 200 and 900 nm under the normal incident angle.     

InP substrate protection and cleaning in liquid phase epitaxy

The interest in single mode lasers for the 1.3–1.55 μm wavelength region prepared by liquid phase epitaxy requires the growth onto non-planar structured InP substrates. A technique for substrate protection to eliminate thermal degradation prior to growth, together with a thermal oxide desorption, is shown to be very effective for this purpose. Characterization of the InP+Sn protection system and results of substrate protection with different techniques are reported. The effectiveness of the method is demonstrated by SEM observations, X-ray double crystal diffraction measurements and results on DH broad area lasers.     

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180?°C for 24 h by using a P source of P(N(CH(3))(2))(3). The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.     

Investigations on the nucleation parameters of InGaAs grown on InP during LPE

The initial stages of LPE growth of the InGaAs ternary compound on an InP substrate were analysed using the classical heterogeneous nucleation theory, incorporating lattice mismatch between the grown alloy and the substrate. The explicit expression for the lattice mismatch induced supercooling for the growth of the chosen system was established, and it was used to evaluate the nucleation parameters. It has been proved theoretically that the nucleation barrier for the formation of InxGa_{1 –x} As on InP depends very strongly on the composition of the alloy; the condition for the growth of good quality InGaAs on InP was calculated.     

Mechanisms of molecular beam epitaxy growth in InAs/InP nanowire heterostructures

InAs/InP axial nanowire heterostructures were grown by the Au-assisted vapour-liquid-solid method in a gas source molecular beam epitaxy system. The nanowire crystal structure and morphology were investigated by transmission electron microscopy for various growth conditions (temperature, growth rate, V/III flux ratio). Growth mechanisms were inferred from the InAs and InP segment lengths as a function of the nanowire diameter. Short InAs segment lengths were found to grow by depletion of In from the Au particle as well as by direct impingement, while longer segments of InAs and InP grew by diffusive transport of adatoms from the nanowire sidewalls. The present study offers a way to control the lengths of InAs quantum dots embedded in InP barriers.     

Effect of deposition conditions on the InP thin films prepared by spray pyrolysis method

InP thin films were prepared by spray pyrolysis technique using aqueous solutions of InCl₃ and Na₂HPO₄, which were atomized with compressed air as carrier gas. The InP thin films were obtained on glass substrates. Thin layers of InP have been grown at various substrate temperatures in the range of 450–525°C. The structural properties have been determined by using X-ray diffraction (XRD). The changes observed in the structural phases during the film formation in dependence of growth temperatures are reported and discussed. Optical properties, such as transmission and the band gap have been analyzed. An analysis of the deduced spectral absorption of the deposited films revealed an optical direct band gap energy of 1.34–1.52 eV for InP thin films. The InP films produced at a substrate temperature 500°C showed a low electrical resistivity of 8.12 × 10³ Ω cm, a carrier concentration of 11.2 × 10²¹ cm⁻³, and a carrier mobility of 51.55 cm²/Vs at room temperature.     

Self-assembling InAs and InP quantum dots for optoelectronic devices

Stranski–Krastanov growth in molecular beam epitaxy allows the preparation of self assembling InAs and InP quantum dots on GaAs and Ga_0.52In_0.48P buffer layers, respectively. InAs dots in GaAs prepared by slow growth rates and low temperature overgrowth provide intense photoluminescence at the technologically important wavelength of 1.3 μm at room temperature. Strain induced vertical alignment, size modification and material interdiffusion for stacked dot layers are studied. A blue shift of the ground state transition energy is observed for the slowly deposited stacked InAs dots. This is ascribed to enhanced strain driven intermixing in vertically aligned islands. For very small densely stacked InP and InAs dots the reduced confinement shift causes a red shift of the ground state emission. The InP quantum dots show intense and narrow photoluminescence at room temperature in the visible red spectral range. First InP/Ga_0.52In_0.48P quantum dot injection lasers are prepared using threefold stacked InP dots. We observe lasing at room temperature in the wavelength range between 690–705 nm depending on the size of the stacked InP dots.     

Thermal conductivity of InAs quantum dot stacks using AlAs strain compensating layers on InP substrate

The growth and thermal conductivity of InAs quantum dot (QD) stacks embedded in GaInAs matrix with AlAs compensating layers deposited on (1 1 3)B InP substrate are presented. The effect of the strain compensating AlAs layer is demonstrated through Atomic Force Microscopy (AFM) and X-ray diffraction structural analysis. The thermal conductivity (2.7 W/m K at 300 K) measured by the 3ω method reveals to be clearly reduced in comparison with a bulk InGaAs layer (5 W/m K). In addition, the thermal conductivity measurements of S doped InP substrates and the SiN insulating layer used in the 3ω method in the 20–200 °C range are also presented. An empirical law is proposed for the S doped InP substrate, which slightly differs from previously presented results.     

InP量子点的掺杂及其光学性能

采用原位成核掺杂法合成了Li、Zn金属离子掺杂的InP量子点(分别记为Li: InP和Zn: InP), 并研究了掺杂剂对量子点的结构、尺寸和光学性能的影响。研究结果表明, Li⁺、Zn²⁺掺杂的InP量子点结晶度较高且尺寸均匀。虽然Li⁺掺杂未引起InP量子点的结构发生变化, Li⁺未进入InP晶格, 但是抑制了InP量子点的成核与长大, 使其吸收谱和荧光谱均发生大幅度的蓝移。Zn掺杂同样也抑制InP量子点的成核与长大, 并且形成InP/Zn₃P₂/ZnO复合核壳结构, 显著增强了InP量子点的荧光, 尤其是当Zn掺杂浓度(Zn/In原子比)为0.2时, InP量子点的荧光强度增加近100多倍, 这对短波长InP量子点的合成具有一定的参考价值。     

Site-controlled growth of InP/GaInP quantum dots on GaAs substrates

A technology platform for the epitaxial growth of site-controlled InP quantum dots (QDs) on GaAs substrates is presented. Nanoholes are patterned in a GaInP layer on a GaAs substrate by electron beam lithography and dry chemical etching, serving as QD nucleation centers. The effects of a thermal treatment on the structured surfaces for deoxidation are investigated in detail. By regrowth on these surfaces, accurate QD positioning is obtained for square array arrangements with lattice periods of 1.25?μm along with a high suppression of interstitial island formation. The optical properties of these red-emitting QDs (λ?～?670?nm) are investigated by means of ensemble- and micro-photoluminescence spectroscopy at cryogenic temperatures.     

On the location of the misfit dislocations in InGaAs/InP mbe single heterostructures

The depth location of the misfit dislocations in InGaAs/InP single heterostructures grown by molecular beam epitaxy has been studied; selective chemical etching and defect observation by cathodoluminescence have been used. It has been found that the misfit dislocations are located inside the InP substrate over a region of a few μm. This result is the opposite of that predicted by the commonly accepted theoretical models for the calculation of the misfit stress in heterostructures.     

Hexagonal geometric patterns formed by radial pore growth of InP based on Voronoi tessellation

To fabricate ordered geometric patterns consisting of InP nanoporous structures, a photoresist mask with periodic opening arrays was prepared by sphere photolithography. The diameter and interval of the openings of the photoresist mask could be controlled independently by adjusting the diameter of silica spheres used as a lens and the exposure time. Through this resist mask with a two-dimensional (2D) hexagonal array of openings, the pore growth of InP during anodic etching was investigated. The isolated openings could act as initiation sites for the radial growth of pores, resulting in the formation of hexagonal geometric patterns based on Voronoi tessellation in 2D space. With further anodic etching, inside the substrate, the growth direction of the pores changed from radial to perpendicular relative to the substrate. Moreover, by removing domains consisting of nanopores by anisotropic chemical etching, the fabrication of InP microhole arrays with circular and triangular cross sections was also achieved.