Tris-(8-hydroxyquinoline) aluminum III (Alq3) is a stable metal chelate that has received a great deal of attention over the past years due to its use in the fabrication of organic light emitting diodes (OLED).[1,2] Despite all the interest in this remarkable material very little information on its' solid-state properties and packing exists. Nearly all of the available information comes from studies that have been carried out on vacuum deposited thin films.[1]

Single ZnO nanowire metal-oxide semiconductor field effect transistors (MOSFETs) were fabricated using nanowires grown by site selective Molecular Beam Epitaxy. When measured in the dark at 25°C, the depletion-mode transistors exhibit good saturation behavior, a threshold voltage of ∼-3V and a maximum transconductance of order 0.3 mS/mm. Under ultra-violet (366nm) illumination, the drain-source current increase by approximately a factor of 5 and the maximum transconductance is ∼ 5 mS/mm. The channel mobility is estimated to be ∼3 cm2 /V.s, which is comparable to that reported for thin film ZnO enhancement mode MOSFETs and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination.

Ce activated SrS has been prepared from SrSO4:Ce(SO4)2.4H2O by ecologically acceptable carbothermal reduction in the absence of inert gas and hazardous H2S environment. The mixtures were fired at 900°C to find out the feasibility of the reduction reaction. In order to understand the compensator behavior we tried with sulfur and various fluxes viz., NH4Cl, NaCl. The materials synthesized were characterized by XRD, photoluminescence emission (PL) and excitation spectroscopy (PLE) and SEM. The characterization results showed the formation of SrS at 900°C with an increase in luminescence intensity after the addition of sulfur as a co-activator. The bright blue-green emission observed at 480nm and 540nm corresponds to energy bands originating from 2T2g (5d) to 2F7/2, 2F5/2(4f) of Ce3+ transitions. The excitation spectrum shows a fundamental absorption of SrS host crystal lattice in the lower wavelength region at 283 nm and Ce at 430 nm.

Photoluminescence (PL) efficiency of thioglycolic-acid (TGA)-stabilized CdTe nanocrystals in water depends strongly on the amount of TGA upon synthesis. The less the amount, the higher the PL efficiency obtained if the colloid is not precipitated. When the molar ratio of TGA against Cd2+ upon preparation is ca. 1.3, PL efficiency of as-prepared solution becomes the maximum and exceeds 60% in red-emitting region. In this case, the spectral widths of the PL become the minimum. We have encapsulated these highly luminescent nanocrystals into glass matrices by using a sol-gel method. Silane coupling agent having an amino-group is effective to preserve the surface of the nanocrystals. The glass thus prepared is stable and shows PL efficiency as high as 40%.

A method to bond directly Indium Phosphide to Indium phosphide at low temperatures has been realized. The treatment of wafers in HF and oxygen plasma exposure prior to bonding is helpful in activating the surface of the wafers at room temperature. This surface activation is useful to bond the wafers at room temperature. Further higher temperature (220°C) treatment with pressure, aided in the completion of the wafer bonding process. The interface of the bonded structures revealed a very thin amorphous layer of oxide when examined under high resolution TEM. Cross-sectional micro Raman measurements revealed signatures corresponding to some disordered associated layer at the interface. Current-Voltage characteristics exhibited ohmic conduction across the interface. The wafer bonding method developed would serve as a useful tool for the fabrication of photonic and optoelectronic devices.

The performance of detectors and sensors is degraded by dark current generation, which is due to defects and impurities in the materials. Electric fields enhance the generation from the resulting deep levels. When the electric field is in the mid-105 V/cm range, the present work finds enhancements of the order of 100 or more for iron and gold in silicon. The activation energy of the generation rate as a function of temperature is seen to decrease when the electric field increases. Many detectors have pixels that form a charge packet before the detectors are read out. Since the presence of charge decreases the electric field, the electric field enhancement varies with time. This is modeled for iron in silicon with an illustrative charge versus electric field relation. The resulting activation energy is found to be barely affected.

We fabricated a DC inorganic electroluminescent (EL) device whose structure is ITO electrode / ZnS:Mn / ZnO (Mn) nanorods / p−/p++-Si(111) / Au electrode. ZnO nanorods were grown by chemical vapor deposition method combined with laser ablation. ZnS:Mn and ITO were deposited by electron-beam-deposition. We studied on annealing effects of ZnO nanorods on the electrical and electroluminescent characteristics of this device. The device without annealing showed a low breakdown voltage, and any EL emission could not be observed. On the other hand, the device with annealing showed higher impedance and higher breakdown voltage, and the EL emission from the ZnS:Mn layer was observed. An intense EL emission was observed from a peripheral of ITO electrode. An EL emission from the inside area of ITO electrode was very weak.

The results of the work on the technology and characterization methods of resonant cavity enhanced (RCE) photodiode heterostructures with strained InxGa1–xAs quantum wells (0.65≤x≤0.82), designed for the 1.8 - 2 μm spectral range, are presented. The heterostructures grown on InP by metalorganic chemical vapor deposition have been investigated by high-resolution X-ray diffraction with synchrotron source, transmission electron microscopy, photoluminescence and reflectivity spectra measurements. Non-resonant photodiodes fabricated from these epitaxial structures exhibit dark current densities below 10-6 A/cm2 and quantum efficiencies above 1 % (even without bias). These quantum efficiency values are a good basis for the resonant cavity enhancement. The optical field enhancement at quantum wells has been examined in resonant heterostructures before processing.

The formation of InAs self-assembled quantum dots on (110) GaAs substrates is demonstrated. These dots form with significantly lower densities than InAs dots grown on (100) GaAs. The low density growth mode of these InAs nanostructures allows for the fabrication of devices capable of electroluminescence from individual quantum dots. Such a device has been fabricated with conventional photolithography and its emission spectra characterized. Additionally, because GaAs cleaves naturally along the (110) crystal plane, the ability to grow InAs quantum dots on (110) GaAs substrates allows for the growth of these dots on the cleaved edges of GaAs first growth samples containing InGaAs strain layers of varying thickness and In fraction. 100% linear alignment of InAs quantum dots over these InGaAs strain layers is demonstrated.

We present an approach for spectroscopic strain analysis in semiconductor quantum-well devices. This approach is applicable to all types of semiconductor materials, and to spectroscopic techniques which employ the electronic band-structure of the material, such as photoluminescence, photoreflection, photocurrent, and transmittance. The approach is based on two components, namely the theoretical calculation of the strain-sensitivity of the spectral positions of the relevant quantum-confined optical transitions within a particular quantum-well, and the spatially resolved measurement of a substantial part of the optical transition sequence within the quantum-well. The primary experimental technique applied in our approach is photocurrent spectroscopy. InAlGaAs/GaAlAs/GaAs, high-power lasers serve as the model species.

Gratings in GaAs/AlGaAs mid-infrared quantum cascade lasers (QCLs) are fabricated with a structure depth of more than 10 μm. A N2/SiCl4 inductively coupled plasma reactive ion etching (ICP-RIE) process was employed to achieve extremely smooth sidewalls and selectivities to the SiNX etch mask of up to 70:1. EDX spectra measured on as-etched samples show that sidewall etch inhibition is caused by a thin Si containing layer on the sidewalls that is formed simultaneously with ICP etching of GaAs at the bottom of the trenches. To demonstrate device application gratings with a pitch of 1.72 μm are applied to long rib waveguide -based QCLs emitting at λ = 10.7 μm. When etched laterally together with the rib the grating gives rise to stable single mode emission up to 295K from these QCLs. The respective grating coupling coefficient is determined to be κ = 29 cm-1.

Recently, a simple method has been developed to obtain inverted GaAs/AlGaAs quantum dots (QDs) below a quantum well (QW) via multi-step (hierarchical) self-assembly [1]. Here we report on the optical characterization of a series of structures GaAs QDs with different size. The study is performed by means of reflectance (R) down to T=15 K, photo- and thermo-reflectance (T>80 K) and by spectroscopic ellipsometry (at RT). Such measurements allow us to check the thickness and composition of the barrier layers and to complete the study of the electronic states involved in the emission properties of QDs and QW levels. QW states were well identified and their energies and shift with the size parameters well agree with the photoluminescence (PL) data. The identification of QD states seems less straightforward in R measurements and deserves further investigation.

High levels of electrical activation of both p- and n-type dopants are realized by pre-amorphization implantation (PAI) in bulk germanium wafers and germanium-on-insulator (GOI) substrates. In bulk germanium, p-type dopant yields an electrical activated concentration of 1.5×1020 /cm3 after a 400°C rapid thermal annealing (RTA), which is one order higher than obtained for samples without PAI. N-type dopants also show comparable improvement as 1×1020 /cm3 after 600°C RTA. Both results are the highest ever being reported and are sufficient for advanced CMOS applications. PAI was also employed in dopant activation for GOI substrates. Carrier concentrations of 6×1020 /cm3 and 5×1019 /cm3 were observed for p- and n-type dopants respectively after identical RTA conditions as for bulk germanium counterparts. Hydrogen incorporated in GOI wafers which were prepared by Smart-Cut™ approach may be responsible for the discrepancy of activated concentrations between bulk germanium and GOI. Nevertheless, PAI shows the promise of dopant activation in germanium and can be readily adopted in current CMOS processes.

We present first-principles calculated electronic and optical properties of some SiGe alloys. The ground-state, electronic excitations and optical properties have been calculated with Ge and Si atoms arranged in different ways among the sites of a diamond-type lattice. For the ground state a DFT-LDA scheme and for the electronic excitations a DFT-GW approach have been respectively used. For the optical properties the DFT-LDA-RPA scheme has been applied for alloys going in composition from Si(100%) to Ge(100%): obtained results have been compared with existing experimental and theoretical data. For the noticeable Si(50%)Ge(50%) alloy also two-particle effects have been evaluated using the Bethe-Salpeter equation.

This paper presents the results of investigations on the influence of sulfur doping on properties of gallium selenide crystals, grown by the Bridgman method from melts with sulfur content of 0.01–3 mass %, using the Hall effect, optical absorption, photoconductivity and microhardness measurements on GaSe: S. The results obtained are explained by assuming the formation of solid solutions of GaSxSe1−x and the presence of the competitive processes of point defects and structural disorder formation.

A high performance of wavelength 870nm resonant cavity LED (RCLED) was fabricated. The high performance of InGaAs/GaAs multiple quantum wells (MQWs) and distributed Bragg reflector (DBR) were employed to achieve the high transmission rate. Two devices A and B were fabricated in this paper. Device A has an offset of 10nm between active region gain and resonant gain, and device B without it. Due to the wavelength shift of active region gain is faster than that of DBR's resonant gain at higher temperature. Device A shows the better temperature performances than device B. A cutoff frequency of 60MHz, a low forward voltage of 1.6V, a output power of 1mW at 10mA and a output power temperature variation (ΔP/ΔT) of –0.02dBm/ °C with chip dimensions of 220um × 220um and 85um diameter emitting window are obtained.

The emission from bias voltage driven In0.06Al0.08Ga0.86As/Al0.3Ga0.7As edge-emitting diode lasers with cavity lengths of 0.6 and 0.9 mm was measured at 290 K using a high resolution Fourier-transform infrared spectrometer. The light-current (L-I) characteristic curves showed that a threshold current of ∼ 0.5 and 0.8 A was needed to reach the stimulated emission in laser diodes with cavity lengths of 0.6 and 0.9 mm, respectively. The laser diode longitudinal modes were observed in the stimulated emission spectrum for each of the devices. These spectra enabled us to calculate the refractive index, total loss, and gain of the active region. On the other hand, the cavity length was determined by utilizing the interferogram spectrum, longitudinal modes spacing, and direct measurements of the laser dimensions. A good agreement between the cavity length values obtained from the three methods was achieved.

Carbon nanomaterials have been prepared using a simple production method of pulsed arc discharge between pure graphite electrodes in liquid. High-resolution transmission electron microscopy observation revealed that two kinds of nanomaterials can be produced in liquid. One of them is powdery products floating on the water surface, and another one is bulky deposits sank down in the water bottom. Some of them have multi-walled carbon nanofibers. Mean diameter of the nanofibers was approximately 30 nm. Optical emission of C+(426.7nm), Hα(656.3nm), Hβ(486.1nm), Hγ(434.0nm), C2 swan bands and CO(457.1nm) can be observed in the arc discharge by using photonic multichannel spectral analyzer. These results indicate that the carbon nanomaterials have been produced by pulsed arc discharge in liquid.

We report here studies of the thermal stability of InGaAs quantum dots that have been subjected to various thermal treatments. Atomic force microscopy and photoluminescence spectroscopy are used to analyze the effects of the thermal treatments. In this paper we present data that demonstrates a remarkable improvement in the thermal stability of quantum dots that were rapidly cooled down to room temperature following the growth of a GaAs capping layer. The observed thermal behavior is attributed to metastable states formed during post growth thermal cycle.

Structural and electronic transport properties of polycrystalline ZnO thin films, prepared by pulsed laser deposition, have been investigated. The films were deposited on glass and Si3N4/Si substrates using O2 and N2 atmospheres. X-ray analysis revealed preferential c-axis orientation perpendicular to the sample substrate. Films deposited under relatively high O2 pressure were highly resistive. However, the conductivity σ increased while the films were irradiated with ultraviolet light, showing an Arrhenius (In σ ∝ T-1) dependence as a function of temperature. The ZnO film deposited in N2 atmosphere exhibited at room temperature a resistivity ∼ 1 Ω cm, and a sheet carrier concentration ∼ 5 1012 cm-2. The variation of the conductivity with temperature, in the range 60 – 150 K, follows a In σ ∝ T-1/4 dependence characteristic of variable range hopping. An analysis of the experimental results of conductivity as a function of temperature, in terms of possible doping effects, as well as conduction mechanisms is presented.