Analysis of high indium concentration in interdiffused In0.65Gs0.35As/GaAs multiple quantum well (MQW) structure on GaAs Substrate is being studied. This material can achieve operating wavelengths around 1.5gtm Ifor applications in fiber optics communications. The large lattice mismatch problem (over 4.5% in this study) can be solved by using a linearly-graded InGaAs buffer layer for reducing any dislocation between the adjacent layers. Interdiffusion in the MQW structure can modify the composition profile in order to tailor the optical absorption and refraction properties. Results show that this system can have promising device performance operates at around 1.55μm and which base on the more matured and reliable GaAs technology.

Using the fundamental transition state, we will investigate the two phase interdiffusion of group V sublattice in a strained lattice matched InGaAs/InP quantum well (QW) structures. The model employs three parameters namely the diffusion coefficients in the barrier (Db)and in the well (Dw)and the concentration ratio (k) of the diffused species at the heterstructure. The QW model includes the effects of strain and the exciton. A pseudo time dependent calculation is also considered and results are fitted to the reported experimental data. These parameters which characterize the diffusion mechanism can be measure to form a better understanding of the interdiffsion process for group V sublattice.

We examine the microstructure of short-period (14–31 Å) composition modulations in epitaxial ZnSel-xTex (x@0.5) films grown by molecular-beam epitaxy (MBE) on vicinal (001) GaAs. Transmission electron microscope (TEM) images of cross-sections reveal highly-periodic contrast along the growth direction throughout the full thicknesses of the films (over 2 μm) that corresponds to a nearly sinusoidal variation between Se- and Te-rich compositions. Growth of ZnSe1-xTex at 285°C on substrates tilted 4° toward [1111 maximizes the strength and regularity of the modulation. Using dynamical electron-diffraction simulations, we estimate a modulation amplitude of r@0.184(7) in a sample showing strong modulation. We assume a small amplitude of strain modulation to fit the experimental data.

Extremely flat layers of GaP were grown on 4° miscut (100) Si substrates by selective Metal- Organic Vapor Phase Epitaxy. An enhancement of Re@3 was measured at the growth edges, which corresponds to a Sherwood number of 12.5. Defect-free growth is obtained at the edge of the silicon nitride mask. A gradual transition to growth with a large defect density is observed with increasing distance from the mask edges. In the defect free areas, a recovery of the (100) crystal plane is consistently measured on top of the grown mesas. This seems to indicate a pure layer-bylayer homoepitaxial mode (Frank-van der Merve mode) after the island mode nucleation (Volmer- Weber mode) on Silicon is completed, forming a thin smooth seed layer. High Resolution TEM shows a uniform Si-GaP transition. Micro-Raman Spectroscopy with spatial resolution of ˜1 micrometer was performed to assess the crystal quality as a function of the distance from the growth edge.

An emission line which depends on the simultaneous presence of excitons and < 2×1010 cm−2 free photoexcited electrons in a 20 nm quantum well is shown to be due to the recombination of free negatively charged excitons ( “trions”). The binding energy is 1.3 meV and the lifetime is 1/4 that of the exciton. The increase in the radiative decay times of excitons and trions with increasing bath temperature is consistent with that of free particles. More directly, from time- and spatially-resolved measurements, we find that trions are localized at 5 K, and with increasing bath temperature both excitons and trions become mobile. The diffusivity of trions and excitons increases linearly with bath temperature, and at 10 K, the trion diffusivity is found to be factor of two lower than the exciton diffusivity. Our results are the first direct experimental evidence for free trions in GaAs quantum wells.

We have developed a Multi-component Zone Melting method to grow a ternary compound crystal which has a uniform composition. A 4.5 mm long InGaAs bulk crystal with a uniform InAs composition of 0.3 has been successfully grown using this method. InGaAlAs/InGaAs strained quantum well lasers were fabricated on an In0. 2Ga0.8As substrate which was grown by this method. A minimum threshold current density of 280 A/cm2 was achieved.

We report the optical characteristics of 100 A˚ thick GaAs/Ga0.521n0.48P single quantum wells grown by Metal Organic Vapor Phase Epitaxy. We have confirmed from the 77 K photoluminescence (PL) that an optimum growth sequence is necessary to achieve the emission from the well (1.52 eV), otherwise only the deep emission band (1.46 eV) is observed. From the time-resolved photoluminescence and temperature dependent PL measurements, we assign that this 1.46 eV deep emission is a recombination of electron-hole pair in a vacancy-related defect which is spatially distributed at the imperfect GaAs/Ga 0.521n0.48P interface.

Semiconductor superlattices have been studied by grazing incidence x-ray scattering and x-ray diffraction. For superlattices of 100-period InGaAs/GaAs, lateral structural ordering has been found to occur in the material. For one particular sample (M1400), periodic thickness modulations have been observed in the InGaAs layers. X-ray results also provide evidence for an improvement of interface quality by using interrupt-growth method for 55-period AlAs/GaAs superlattices grown by MBE.

Distributed Bragg reflectors composed of InGaAs/InAlAs alternating layers have been grown on InP substrates by MOCVD. To obtain high performance, the growth condition has been traded off between surface roughness and crystal quality. Using in-situ laser reflectometry, the precise control of layer thickness and composition has been achieved for reproducible DBR growth. The optimal mirror performance and sharp interfaces have been observed in the DBR grown at 650'C. In order to avoid band-edge absorption 6% of Al has been added to In 0.53Ga0.47As to produce quarternary In0.53Ga 0.41Al 0.06As/InAlAs Bragg reflector exhibiting high reflectivity at 1.55 μm.

Single layers of ZnSe, ZnSxSe1−x., and Znl−y.MnySxSe1−x., were grown on the GaAs(001). Realtime reflection high energy electron diffraction was used to study the initial growth of ZnSe(001) on GaAs(001) under different conditions. Exposure of the GaAs substrate to Se flux before growth led to three-dimensional growth, whereas exposure to Zn flux led to two dimensional-growth. ZnSxSe1−x., and Znl−y.MnySxSe1−x., (energy gap less than 2.9 eV) layers with the lattice constant closely matched to that of GaAs have been grown with a good reproducibility.

In this paper we have studied, the Burstein-Moss shift (BMS) in quantum wires (QWs) and quantum dots (QDs) of ternary and quaternary types of optoelectronic materials on the basis of a newly formulated electron dispersion law which occours as a result of heavy doping. It has been found, taking Hg1−xCdx.Te and In1−x.Gax.AsyP1−y lattice matched to InP as examples, that the BMS increases with :Lncreasing electron concentration and decreases with increasing film thickness in oscillatory manners for both types of quantum confinements, although the variations are totally band structure dependent. The numerical values of BMS is greatest in QDs and least in QWs together with the fact that the BMS in quaternary materials is greater than that of ternary comupounds. In addition the theoretical analysis is a quantitative agreement with the experimental datas as given elsewhere.

Availability of tensilely strained GaInP/AIGaInP quantum well, which is essential to laser diodes operating at 635–650nm, is investigated by combining conventional and time-resolved photoluminescence measurements. It is found that optical characteristics are improved by introducing tensile strain into barrier layers in addition to well layers, while samples with unstrained or compressively strained barrier layers reveal inferior characteristics. Experimantal data indicate that these optical characteristics are not determined by interfacial stress, but by the energy band discontinuity between well and barrier layer.

A multiple-quantum barrier (MQB) structure has been applied to AlGaAs superluminescent diode (SLD) to suppress the electron overflow from active to cladding region at elevated temperatures. It was found that the presence of MQB in the p-cladding region leads to stagnant hole transport to the active region. To improve the hole transportation, we propose a new quantum structure for active region. In this design, the superlattice structure MQB is located in the middle of active region which allows smooth hole injection to the active from the cladding region. Carriers can reach both side of the MQB structure in the active region by tunneling phenomenon which critically depends on the barrier thickness. Simulation results show that low energy electrons can tunnel through the MQB barriers, while high energy electrons are reflected back by effective barrier. Finally, multiple-quantum well (MQW) structure is integrated at each side of MQB to minimize the possible over-flow of tunneled electrons and to improve the radiative efficiency of the SLD device. Experimental data support the visibility of the proposed ‘MQB+MQW in Active’ structure at elevated temperatures.

We report the crystal growth conditions and lasing characteristics of InGaAs-GaAs strained-layer quantum well vertical cavity surface emitting lasers (VCSELs) grown on GaAs(311)A substrates by molecular beam epitaxy. A significantly smooth surface and high reflectivity of more than 99 % were achieved. Very flat and dislocation-free AlAs/GaAs hetero-interfaces were obtained. Furthermore, a very low threshold of 5.5 mA and current density of 270 A/cm2 have been achieved for the first time under CW operation at room temperature. In addition, we demonstrate stable polarization characteristics at high currents. These results are believed to be a consequence of both the predicted high gain and anisotropic gain distribution on the (311) surface.

In this work we report a systematic study of the effect of oxygen on ytterbium 4f- 4f emission by coimplanting Yb and O into InP. The PL spectra of InP: Yb and InP: (Yb+O) as a function of annealing temperature and duration were studied. In addition the photoluminescence and kinetic processes were investigated as a function of temperature and excitation intensity.The investigation shows that the codoped oxygen reduces drastically the Yb3+ emissioon from SI and n-type InP:Yb under intrinsic excitation. The codoping of Yb and 0 may create a complex involving a YbIn and Op. This structured isoelectronic (YbIn- Op) complex, may behave as a deep trap (or a deep donor) located approximately at the middle of bandgap. Exciton bound to such centers will not have sufficient energy to excite the core Yb 4f electrons by Auger direct energy transfer process.

Dislocations in LiB3O5(LBO) single crystal were investigated by white-beam synchrotron radiation topography(WBSRT). The WBSRT revealed that the grown-in dislocations are mainly pure screw or edge types with the Burgers vectors in the low index directions on (010) lattice plane. Based on the structure analysis, the formation cause of dislocations can be interpreted in terms of the loose packing of B-O rings and the low density of Li+ on (010) lattice plane.

Effects of convective mixing on the concentration homogeneity of the crystal has been demonstrated. Insitu observations of the solid liquid interface shape during crystal growth are presented which can be used to optimize the dopant distribution. Observations of the interface during growth are discussed varying the parameters in a controlled manner to minimize the thermosolutal effects. It has been observed that beyond a critical velocity for the particular dopant level, the interface shape changes. The change in the interface shape can be related to the fluid flow in the melt. Two different instability regions, namely convective and morphological are addressed. Experimentally observed result are compared with the existing convecto-diffusive theories.

Domain inverted structures in LiNbO3 (LN) and LiTaO3 (LT) are fabricated by proton exchange followed by rapid heat treatment. The formation and development of the effects of pyroelectric field on domain inversion are investigated. The proton and lithium profiles are measured by SIMS. The Curie temperature of the proton exchanged LT is evaluated by DSC. An internal electric field model is proposed to explain the domain inversion mechanism.

The influence of water molecules adsorbed at the surface of electrochromic WO3 films on film stability in aqueous electrolyte has been studied by scanning electron microscopy and high energy electron diffraction.

Luminescent a-Si:O:C layers were obtained by magnetron co-sputtering and annealing. Maximum photoluminescence intensity is comparable to that of porous silicon. Luminescence maximum is between 1.8 eV and 2.2 eV. X-ray photoelectron spectroscopy (XPS) finds Si-O, C-Si and C-C bonding. Secondary ion mass spectrometry(SIMS) data are presented.