Local vibrational modes (LVMs) of carbon-hydrogen (C-H) complexes in proton implanted AlGaN grown on sapphire by metalorganic chemical vapor deposition (MOCVD) were investigated using Fourier transform infrared (FTIR) spectroscopy. The LVMs exhibit five distinctive peaks in the spectral region of 2846∼2963 cm−1, which are due to the symmetric and asymmetric stretching modes of C-Hn (n=1–3). The LVMs intensities in doped AlGaN are increased as irradiation dose is increased in the entire irradiation dose range used without reaching the saturation stage. On the other hand, undoped samples show that LVMs intensity increase then either decreased or saturated as the irradiation dose is increased above 5×1016 cm−2. Proton irradiation causes a drastic increase in the CH3 LVM while electron irradiation causes the opposite effect suggesting strongly that the observed LVMs are truly due to CH complexes.

We report on the optical properties of two dimensional (2D) photonic crystals (PCs) deeply etched in an InP/GaInAsP step-index waveguide. Transmission (T) measurements through simple PC slabs and through one-dimensional (1D) Fabry-Pérot (FP) cavities between PC mirrors are reported and compared to theory. A 2D finite difference time-domain (FDTD) method combined to a phenomenological out-of-plane loss model is used to assess different loss contributions. The PC optical properties are deduced from the FP peak analysis. The origin of the high T level observed inside the stopgap is investigated.

PbSe/PbSrSe multiple-quantum-well (MQW) structures and PbSrSe thin films were grown on BaF2 (111) substrates by molecular beam epitaxy (MBE) and characterized by Fourier transform infrared (FTIR) spectrometer. Strong photoluminescence without Fabry-Perot interference fringes was observed even at room temperature from the MQW structures. The peak energies for the MQW structures with different well widths shifted to high energy with increasing temperature. The absorption edge of PbSrSe layer was determined by transmission spectra. Meanwhile, we designed and fabricated λ=4.1 μm MQW vertical cavity surface emitting laser (VCSEL). A power output of 40 mW was obtained at room temperature. The room temperature threshold pump density is 200 kW/cm2.

It is necessary to clarify the effect of Marangoni convection on single crystal growth from a melt in order to improve the quality of the grown crystal. Particularly, the deviation of crystalmelt (C-M) interface from a planar shape is a major problem because it may deteriorate the quality of the grown crystal. In this paper, we investigated the effect of thermal and solutal Marangoni convection on C-M interface shape in an In-Sb binary system by the horizontal Bridgman (HB) method. The C-M interface concavity strongly depends on the cooling rate and the temperature gradient under uniform concentration distribution conditions in the melt. A large concavity was observed at low cooling rates and high temperature gradient conditions. The concavity was found to be caused by thermal Marangoni convection, by taking Péclet number into account. Then, we varied the composition of the In-Sb binary system to induce solutal Marangoni convection intentionally. The C-M interface was kept planar in case solutal Marangoni convection occurred in the direction opposite to the thermal one. Therefore, we believe that the utilization of solutal Marangoni convection will be a new control technique to make the C-M interface planar for the HB system. From these results, it was clarified that Marangoni convection plays a significant role in the HB crystal growth system.

The ternary chalcopyrite semiconductor Cu(In/Ga)(Se/S)2 is currently used as an absorber layer in high efficiency thin film solar cells. In this study, various types of I-III-VI (I = Cu, III = Ga or In, VI = S or Se) thin films (CuGaS2, CuInS2 and CuInSe2) were prepared from a series of organometallic precursors, M[(S/Se)2CNMeR]n (M = Cu, In, Ga; R = alkyl) by aerosol-assisted chemical vapour deposition (AACVD). In contrast to the metal alkyl compounds, MR3 (M = In and Ga; R = alkyl), which are pyrophoric, the precursors are easy to synthesize by one-pot reactions and are air stable. The optimum growth temperature for the preparation of these films on glass substrates using aerosol-assisted chemical vapour deposition (AACVD) was found to be above 400 °C in terms of crystallinity, although deposition does occur at lower temperatures. The films have been characterised using XRPD, SEM and EDS. SEM analyses show all films are microcrystalline. XRPD results show evidence of the crystalline nature of theses films. The results of this comprehensive study are presented and discussed.

An investigation of the physical mechanisms governing the response of III-V based solar cells to particle irradiation is presented. The effect of particle irradiation on single and multijunction solar cells is studied through current vs. voltage, spectral response, and deep level transient spectroscopy measurements. The basic radiation response mechanisms are identified, and their effects on the solar cell electrical performance are described. In particular, a detailed analysis of multijunction InxGa1-xP/InyGa1-yAs/Ge devices is presented. The MJ cell response is found to be more strongly affected by the internal cell structure than by the In content.

Electron non-radiative recombination process of photoexcited carriers in as-grown and annealed n-Al0.2Ga0.8As/GaAs hetero-structure samples are investigated by using a piezoelectric photothermal spectroscopy (PPTS). The PPT signal above the band-gap energy of GaAs substrate decreased when the sample was annealed at 815°C. In the frequency dependent measurements, the deviations from 1/f linear function are clearly observed in the AlGaAs/GaAs samples. This critical deviation frequency was found to shift to the lower frequency region by annealing. Our experimental results are explained by assuming that the sample annealing generates an unknown deep level in AlGaAs epitaxial layer region and this level effectively traps the photoexcited carriers non-radiatively.

MOS-like structures were obtained by chemical deposition of a polycrystalline PbS thin film on top of a silicon dioxide/Si substrate. Gold ohmic electrodes in coplanar configuration were subsequently deposited by vacuum evaporation on PbS surface (drain and source electrodes). The gate aluminum electrode was deposited on the back of the Si substrate. The dependence of the photoconductive signal, generated in the PbS film, on the gate voltage was studied for wavelengths ranging between 800 nm and 3000 nm at room temperature as well as at low temperatures. It was found that the relative variation of the signal could be as high as 50 % for gate voltages ranging between −30 V and +30 V. Two possible mechanisms are proposed to explain the signal variation with the gate voltage: 1) Variation of the depleted region's thickness in the PbS film, that leads to a variation of the conduction channel's resistance (the reference resistance called, also, the dark resistance), 2) The possible variation of the majority carriers (holes) life-time due to the electron blocking at the PbS/oxide interface when positive gate voltages are applied on the back electrode. Integrated IR detectors with controlled sensitivity in the 800–3000 nm range can be manufactured at a relatively low cost using the PbS/oxide/Si MOS-like structure.

Thermal annealing effects on carbon-hydrogen (C-H) complexes defects in AlGaN grown on sapphire by metalorganic chemical vapor deposition (MOCVD) technique have been investigated using Fourier transform infrared spectroscopy (FTIR). The CH complexes in AlGaN, formed either during growth or by proton irradiation, exhibit five local vibrational modes (LVMs) due to the symmetric and asymmetric vibrational stretching modes of C-H in CHn (n=1–;3) defect complexes. It was found that the annealing temperature (Ta) of 500°C is sufficient enough to dissociate most of the C-H complexes in AlGaN samples. A turning point annealing temperature is found around 300°C for un-irradiated Mg-doped sample, below which the total integrated area of the C-H LVMs continued to increase with increasing annealing temperature and reach the maximum value around 300°C. At Ta > 300°C, the total integrated area of the C-H LVMs starts to decrease and the C-H complexes seem to be completely depleted at Ta > 600°C. The depleted C-H LVMs were observed to partially recover after thermal annealing at Ta > 500°C and waiting for aging periods of several days. This recovery behavior is explained in terms of the hydrogen being remained inside the crystal after the dissociation of C-H complexes, subsequent diffusion and recombining again with carbon atom to reform C-H complexes.

The possibility of the solid solutions with MgO provides the opportunity in ZnO/ZnMgO quantum well structures. The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue for p-doping to form p-n junction devices in ZnO.. We report on the synthesis and structural properties of Zn (Mg,Li)O. The possibility of p-doping by P has been explored.

The incorporation of a high percentage of nitrogen in the GaAs lattice has been the subject of recent interest to reduce the bandgap while maintaining the nearly lattice matched condition to GaAs. We will report on the metalorganic chemical vapor deposition (MOCVD) of GaAsN using trimethylgallium (TMG), tertiarybutylarsine (TBA) and dimethylhydrazine (DMHy) organometallic sources in a hydrogen-free carrier gas. A nitrogen concentration as high as ∼8% in GaAsN was achieved. The effect of nitrogen concentration on the structural, optical and surface properties of GaAsN films will be discussed.

In this paper, ZnO with a rich variety of well-defined morphologies have been achieved by solution route using different kind of precursors, which can prepare particles by only one step without calcination. The influences of solvent, and temperature on the particle size and morphology of ZnO were investigated. It was revealed by the scanning electron microscope (SEM) and transmission electron microscope (TEM) images that the morphological feature of ZnO can be controlled as rod-, polyhedron-, fluffy sphere-, snowflake- and flower-like, etc. XRD measurement showed that all of the ZnO samples with different morphologies has the same hexagonal structure, which is well consistent with electron diffraction (ED) characterization. This communication not only provides promising candidates for materials science due to the importance of shape in relationship with materials, but also presents an effective route to synthesize the well-defined inorganic materials.

We present three-dimensional analysis of two-dimensional guided resonances in photonic crystal slab structures. This analysis leads to a new understanding of the complex spectral properties of such systems. Specifically, we calculate the dispersion diagrams, the modal patterns, and transmission and reflection spectra of these resonances. From these calculations, a key observation emerges involving the presence of two temporal pathways for transmission and reflection processes. Using this insight, we introduce a general physical model that explains the essential features of complex spectral properties. Finally, we show that the quality factors of these resonances are strongly influenced by the symmetry of the modes, and the strength of the index modulation.

We report on a room temperature detector which allows to determine and monitor the state of polarization of terahertz radiation with picosecond temporal resolution. The detector is based on the circular photogalvanic effect recently observed in GaAs/AlGaAs quantum wells. The circular photogalvanic effect yields in response to elliptically polarized radiation a current signal proportional to the degree of circular polarization. The peak current signal occurs in unbiased samples for circular polarization, vanishes at linear polarization and changes sign by switching the helicity from right-handed to left-handed. The detector consists of a (113)A MBE grown p-GaAs/AlGaAs multiple quantum well structure. The response has been measured in the wavelength range between 76 μm and 280 μm at normal incidence of the radiation on the sample.

We have used the variational and fractional-dimensional space approaches in a study of the virial theorem value and scaling of the shallow-donor binding energies versus donor Bohr radiusin GaAs-(Ga,Al)As semiconductor quantum wells and quantum-well wires. A comparison is made with previous results with respect to exciton states. In the case the donor ground-state wave function may be approximated by a D-dimensional hydrogenic wave function, the virial theorem value equals 2 and the scaling rule for the donor binding energy versus quantum-sized Bohr radius is hyperbolic, both for quantum wells and wires. In contrast, calculations within the variational scheme show that the scaling of the donor binding energies with quantum-sized Bohr radius is in general nonhyperbolic and that the virial theorem value is nonconstant.

Experiments on annealing of CdGeAs2-, CdSnAs2- and ZnGeP2-crystals in the vapor of volatile constituents were carried out. Conductivity and Hall effect measurements were performed to characterize the modification of electrical properties, caused by the interaction of the crystal with the gas phase during annealing. Literature data and the results of the present work are discussed based on the results of a quasi-chemical analysis. This yielded that the results of annealing depends essentially on both the conditions of the experiment and the initial imperfection of the crystal. The most probable native structural defects becoming apparent under the annealing were the following: for CdSnAs2 - SnCd, VAs; for CdGeAs2 - VAs, VCd, CdGe, GeCd; for CdSiAs2 - SiAs, VAs ; for CdSiP2 - VCd, VP; for ZnGeP2 - ZnGe, GeZn, VZn, VP; and for ZnSnP2- ZnSn, SnZn, VZn, VP.

The past few years have seen considerable efforts in growth and device application of selfassembled quantum dots. However, the photoluminescence (PL) linewidth, which represents structural fluctuations in dot sizes, is still in the range of 30–50 meV. This large linewidth has deleterious effects on devices such as lasers based on self-assembled dots. In this paper we will examine the configuration-energy diagram of self-assembled dots. Our formalism is based on: (1) an atomistic Monte Carlo method which allows us to find the minimum energy configuration and strain tensors as well as intermediate configurations of dots; (2) an 8-band k·p method to calculate the electronic spectra. We present results on the strain energy per unit cell for various distributions of InAs/GaAs quantum dots and relate them to published experimental results. In particular we examine uncovered InAs/GaAs dots and show that in the uncovered state a welldefined minimum exists in the configuration energy plot. The minimum corresponds to the size that agrees well with experiments.

Growth kinetics and thermodynamic equilibrium can both be determining factors at different stages of III-V semiconductor heteroepitaxy. We study their interplay, employing kinetic Monte Carlo simulations for the InAs(001) surface. The simulation contains atomistic details of both species, including the stability of different reconstructions and their kinetics. The behavior of the surface in thermodynamic equilibrium, including different reconstructions, is determined exclusively by extensive total energy calculations employing ab initio density functional theory. The continuous phase transition between the α?(2×4) and β?(2×4), predicted by theory, is confirmed by experiment. At full layer coverage, a recovery of the stable reconstruction is observed. The different time scales associated with As2 and In are discussed with respect to equilibrium and kinetics.

The main aim of this work is to study electron scattering in imperfect semiconductor heterostruetures. The source of unintentional disorder is the interface roughness at the heterojunctions occurring during growth. In order to achieve this goal we solve numerically the two–dimensional Ben Daniel–Duke equation for the electron scattering problem. Our model assumes open boundary conditions along the growth direction and periodic ones parallel to the heterojunctions. We then compute the reflection and transmission matrices that govern channel mixing due to interface roughness scattering. The knowledge of the mixing matrices allow us to calculate the transmission coefficient in any heterostruc-ture made of wide gap semiconductors. As an example, we compute the transmission coefficient in resonant tunneling devices based on double-barrier structures.

Doping of the lead telluride and related alloys with the group III impurities results in appearance of unique physical features of the material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. We review physical principles of operation of the photodetecting devices based on the group III-doped IV-VI including possibilities of fast quenching of the persistent photoresponse, construction of a focal-plane array, new readout technique, and others. Comparison of performance of the state of the art Ge(Ga) and Si(Sb) photodetectors with their lead telluride-based analogs shows that the responsivity of PbSnTe(In) photodetectors is by several orders of magnitude higher. High photoresponse is detected at the wavelength 116 micrometers in PbSnTe(In), and it is possible that the photoconductivity spectrum covers all the submillimeter wavelength range.