Structural defects in InSb quantum well (QW) samples have been investigated by transmission electron microscopy (TEM). Using molecular beam epitaxy, an InSb QW with remotely-doped Al0.09In0.91Sb barriers was grown on a GaAs (001) substrate with buffer layers consisting of, in order from the substrate: 1 μm of GaSb, 1 μm of AlSb, 50 nm of GaSb-AlSb strained layer superlattice (SLS), and 3 μm of Al0.09In0.91Sb. Cross-sectional TEM analysis indicates that high densities of threading dislocations (TDs) are created at the two highly lattice-mismatched interfaces, the Al0.09In0.91Sb/GaSb-AlSb SLS and the GaSb/GaAs interfaces. Pairs of stereo images taken from plan-view TEM (PV-TEM) specimens show that TDs propagate through the InSb QW layer. The densities of TDs and micro-twin (MT) defects measured by PV-TEM are 9×108/cm2 and 4×103/cm, respectively. These values are worse than those in an InSb QW layer grown with a different buffer layer by a factor of ∼4. The different buffer layer contains an InSb interlayer that effectively filters out both TDs and MTs. Adopting an interlayer structure and reducing the GaSb and AlSb layer thickness may make it possible to fabricate a lower-defect-density yet thinner InSb QW sample with the type of buffer layer examined in this study.

This note reports on a surface field effect transistor, SFET, where the electron channel consists of the interface between vacuum and a Cs-doped glass, and an electrode on the back of the glass substrate is used as the gate. The device has a transconductance of 4×10−10 S cm−1. The transconductance is limited by the glass surface roughness, ∼ 0.4 nm RMS. A reduction of surface roughness to 0.1 nm RMS is expected to increase device transconductance.

SiC homo-epitaxial layers have been grown using a halide chemical vapor deposition (HCVD) process. The thermodynamic process of SiC CVD in SiCl4-C3H8-H2 gas system was studied using equilibrium model. The predicted growth rate decreases gradually with the increase in growth temperature, and this trend is consistent with our experimental results. Good quality epitaxial layers with low density of basal plane dislocations could be grown. Some elementary screw dislocations present in the substrate do not seem to be propagating into the epitaxial layer.

Demand for low cost and high density near infrared (NIR) detection has motivated the development and use of germanium on silicon (Ge/Si) heterostructures to extend the optoelectronic application of Si technology. Ge/Si structures are currently being considered for NIR p/n detectors that can be integrated with Si CMOS [1]. Various research demonstrations of integrated Ge/Si diodes with CMOS have been made including using sputtered poly-Ge to form Ge/Si photodiodes after the CMOS transistors were complete. Poly-crystalline germanium (poly-Ge) may be formed by various methods including the use of plasma enhanced chemical vapor deposition. In this work, the formation of poly-Ge/Si heterostructures by inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) is examined as an alternative method to integrate poly-Ge into a CMOS process flow. In this work, 25 nm poly-Ge on Si heterostructures are formed by either recrystallization of ICP-CVD hydrogenated amorphous germanium (α-Ge:H) or direct deposition of ICP-CVD poly-Ge. A rapid measure of the suitability for detectors of the different poly-Ge films is the minority carrier recombination lifetime, which can affect dark current, quantum efficiency and overall detector detectivity. Recombination lifetimes were measured, therefore, in α-Ge:H that was recrystallized using rapid thermal annealing between 400 – 1050 °C in nitrogen ambient. Lifetimes were measured using a non-contact inductively coupled photo-conductance setup and an effective surface recombination velocity is subsequently extracted for each Ge/Si heterostructure that describes the integrated recombination in the Ge layer and at the Ge/Si interface, which separates the Ge contribution from recombination in the bulk silicon and at the silicon surface. The effective recombination velocities for the 25 nm Ge layers are found to be ∼103−104 cm/s.

The optical band gap related to the electronic structures as well as the refractive index function of the electronic polarizability of the network can be tailored by changing the nature and the number of anions into the vicinity of cations. New routes have been developed in order to prepare new divided Ti(IV)-based oxyfluorinated compounds. In these compounds, the optical absorptions appear at the UV-Vis frontier and the refractive index is always smaller than the one of equivalent oxides. The chemical bonding, the hybridation and the density of the network play key roles in the variation of the optical band gap and the refractive index. For this family of titanium-based oxyfluorides containing mixed anions, chemical compositions and structural features have been correlated to the optical band gap and the refractive index, i.e. the complex index of materials n(λ) + ik(λ). Several examples will be given in order to illustrate the potentialities of these new inorganic compounds by changing the F/Ti ratio and the cationic substitution.

We have successfully developed a new light-trapping scheme for solar cells that can enhance the optical path length by more than 104 times using a textured photonic crystal structure as a backside reflector. Top-contacted crystalline Si solar cells integrated with the new back reflector were designed, fabricated and characterized. Both external quantum efficiency and power conversion efficiency of the cells have shown significant improvement due to the path length enhancement furnished by the new back reflector despite of the 675 um thick wafers and relatively short minority carrier diffusion length.

The influence on defects of Er implanted Al0.70Ga0.30As was studied, using standard Positron Annihilation Spectroscopy (PAS) and Photoluminescence (PL) technique. The incident energy of mono-energetic positrons was implanted from 0.1 eV to 30 keV. The characterization of un-doped Al0.70Ga0.30As and Al0.70Ga0.30As:Er,Yb as implanted, and Al0.70Ga0.30As:Er,Yb annealed ranging from 500 to 900 °C were successfully studied by using PAS technique. Into the incident energy around 5keV, the shape parameter of Al0.70Ga0.30As:Er,Yb annealed ranging from 500 to 900 °C was decreased and the PL intensity also increased in response to the annealing temperature ranging from 500 to 900 °C.

Zinc oxide (ZnO) quantum dots (QDs) embedded films were fabricated on silicon substrates by metal organic chemical vapor deposition at 350°C. The QDs can be obtained in a matrix of amorphous ZnO films by introducing a large amount of precursors. The size of the QDs ranged from 3 to 12 nm, which was estimated by high-resolution transmission electron microscopy. The photoluminescence measured at 80 K showed that the emission of QDs embedded film ranged from 3.0 to 3.6 eV. The broad near-band-edge emission is due to the quantum confinement effect of the QDs. The quantum confinement effect of the QDs disappears after the post-growth annealing due to the ripening of QDs.

The theoretical study reported here is devoted to diluted GaInNAs nitride alloys, and focuses on correlation between local chemical atomic neighborhood and atomic distances. The model used is Valence Force Field approximation, and we model a periodic Ga1−xInxNyAs1−y alloy film deposited on a GaAs substrate. The surface is dimerised (for simplicity we consider 2×1 anion rich surfaces). First starting from a random film, first and second nearest neighbor distances are calculated, and the corresponding histogram drawn. Then a pseudo-annealing process is simulated by allowing the N atoms to choose their optimal location. This pseudo-annealing strongly enhances the number of In-N bonds, in agreement to experimental studies. From this statistical study, fine structure of each peak of the histograms is shown to be not directly related to a given surrounding chemical distribution up to 3rd nearest neighbors. The positions (in distance) of the peaks appear not to be modified by alloy composition nor alloy segregation, which only alter relative intensities and peak shapes. Last, we consider stripes of In-rich and In-poor zones: calculated energy variations show a strong tendency for N atoms to completely desert In-poor zones.

Efficient mid-IR interband cascade (IC) lasers have been developed based on III-V semiconductor materials with lasing emission covering a wavelength range from 2.7 to 5.6 microns. These IC lasers reuse injected electrons in cascade stages for photon generation with high quantum efficiency to achieve high output powers. Also, IC lasers have a low threshold current density with a very efficient use of applied voltage, resulting in reduced power consumption. Single-mode distributed feedback lasers have been made, and integrated into aircraft and balloon instruments which made atmospheric measurements of CH4 and HCl. In this work, the characteristics of IC lasers and their recent developments are reviewed.

We employed the postgrowth impurity-free vacancy diffusion technique to selectively tune the bandgap of the InAs/InGaAlAs dots-in-well laser structure grown on (100) InP substrate. A blueshift up to 170 nm with a significant decrease in the photoluminescence linewidth has been observed. Spatial control of the bandgap shifts has been achieved using SiO2 and SixNy layers as annealing caps. A differential wavelength shift of 76 nm has been observed after a rapid thermal annealing step at 750 °C for 30 s. In contrast to most reported results in other material systems using similar process, we observed a larger bandgap shift from the SixNy capped samples than from the SiO2 capped samples. Our theoretical calculation indicates that the unusual intermixing behavior in this material system is governed by different interdiffusion rates of group-III atoms.

In this study, single crystal ZnO films are grown by pulsed laser deposition and ion beam processing is used alter the resistivity of the films. A 3He ion beam was chosen with a specific energy to transmutate oxygen into nitrogen. Analytical ion beam techniques were used to monitor the transmutation process, and changes in film characteristics were monitored by making resistance, photoconductivity and luminescence measurements before and after ion beam processing. The amount of nitrogen produced by this method was estimated to be ∼ 1014 cm−3, and was too low to be observable as a p-type dopant due to compensation by the naturally n-type material. However, the ion beam processed films improved dramatically in resistivity, defect luminescence was reduced and photoconductivity increases consistent with the improvements with resistivity were observed. These improvements were attributed to ion beam annealing of the crystal resulting in a reduction of point defects. In some films, blistering of the surface occurred and was attributed to the formation of gas bubbles which causes delamination of the film from the substrate.

We report a method to amplify the electron current of carbon nanotube field emitter cathode using an electron multiplier and synthesis of thin multiwall carbon nanotubes by thermal chemical vapor deposition. A commercial microchannel plate which is an array of microscopic electron multipliers was used for this purpose. A microchannel plate placed between the cathode and anode amplified the current and also acted as protection shield for nanotubes during vacuum arcing. The turn-on field was approximately 1 V/µm for both cases, but current obtained was 3 times higher and the field was also lower. The increase in current is attributed to the electron multiplication, and to the increase in field enhancement factor from 9296 to 12815 (37%) with microchannel plate. The thin multiwall carbon nanotubes were synthesized using Mo/Fe catalyst solution. The inner and outer wall diameters of the nanotubes were in the range of 2.5-5 nm and 7-15 nm respectively, determined by Raman spectroscopy and transmission electron microscopy. The nanotubes had excellent field emission property which is attributed to their thin wall diameters ∼10 nm, high aspect ratio of 1500 and the high field enhancement factor of 9296. The emission current was stable with an average fluctuation of 2%.

Metal-induced lateral crystallization of amorphous Si has been investigated under a wide range of electric fields (0-4000 V/cm). In the low field region (<100 V/cm), lateral growth velocity at the cathode side was enhanced by applying an electric field. This achieved formation of poly-Si with a large area (∼50 μm) during low-temperature annealing (525°C, 25 h). When the electric field exceeded 100 V/cm, the lateral growth velocity decreased with increasing the electric field strength. Under the extremely high electric field (>2000 V/cm), directional growth aligned to the electric field was observed. This new findings will be a powerful tool to achieve new poly-Si with highly controlled structures.

Zincblende semiconductor materials such as GaAs and ZnSe are very promising for the generation of tunable IR signals by quasi phase-matched nonlinear optical frequency conversion. Orientation patterned GaAs crystals (OP-GaAs) were grown by low-pressure hydride vapor phase epitaxy (HVPE) on lithographically prepared templates.. Cathodoluminescence (CL) imaging was used to study these epitaxial films, which consist of periodic domains of inverted crystallographic orientation. The challenge is to achieve thick, vertical domains and to minimize sources of optical loss. Both the domain walls and crystal defects may contribute to transmission losses, therefore, a characterization of both is necessary to improve the OP-GaAs crystal performance. The stress and non radiative recombination activity of the domain walls were investigated. The presence of dislocation glide was revealed and CL spectral imaging was used to observe the stress distribution around both the domain walls and the dislocations.

Self-assembled InGaAs quantum dots (QD) grown by metal organic chemical vapor deposition (MOCVD) have a natural peak emission wavelength around 1150-1200-nm due to its specific composition, shapes, and sizes. In this work, a new method to engineer the emission wavelength capability of MOCVD-grown InGaAs QD on GaAs to ∼1000-nm by utilizing interdiffused InGaAsP QD has been demonstrated. Incorporation of phosphorus species from the GaAsP barriers into the MOCVD-grown self-assembled InGaAs QD is achieved by interdiffusion process. Reasonably low threshold characteristics of ∼ 200-280 A/cm2 have been obtained for interdiffused InGaAsP QD lasers emitting at 1040-nm, which corresponds to blue-shift of ∼ 85-90-nm in comparison to that of unannealed InGaAs QD laser.

Mid-IR lasers fabricated from narrow bandgap IV-VI semiconductors are proven devices for molecular spectroscopy applications. Wide single-mode tunability, low waste heat generation, and large spectral coverage from about 1000 cm−1 (10 µm) to about 2500 cm−1 (4 µm) have allowed development of laser absorption spectroscopy instrumentation for fast and sensitive measurement of specific gas phase molecules. For example, IV-VI mid-IR lasers with emission in the 5.2 µm spectral range have recently enabled the development of breath analysis instruments for real-time measurement of exhaled nitric oxide (eNO). Laser tunability with current ramping is sufficient for simultaneous measurement of exhaled carbon dioxide (eCO2), a capability that allows highly accurate determination of eNO concentrations in the low ppb range, a sensitivity required for assessing airway inflammation in patients with asthma. After discussing emerging medical diagnostic applications this paper reviews recent progress in the development of liquid-nitrogen-free cryogenic cooling systems for IV-VI mid-IR lasers. A description of continuing research on the development of improved IV-VI lasers, where the primary objective is to fabricate devices with continuous wave (cw) operation at room temperature is then presented. Theoretical and experimental analysis of (111)-oriented multiple quantum well (MQW) IV-VI materials show that it should be possible to reduce lasing thresholds significantly. In addition, results from transferring IV-VI materials from low thermal conductivity growth substrates to higher thermal conductivity copper show that new laser packaging methods can significantly improve active region heat dissipation. Together, these new materials and device packaging methods promise to enable the fabrication of IV-VI mid-IR lasers with cw operation at room temperature.

Powder X-ray diffraction analyses of Mn-and Cu-doped ZnO powders calcined at 500˚C, show shifts in the wurtzite type semiconductor's lattice constants and unit cell volume which correspond to the nominal concentrations of transition metal dopants. Marked reductions in the a-lattice constant and unit cell volume for a small concentration of Cu dopants, which is not maintained upon increased Cu concentration, suggest a change in the copper ion hybridization state due to the dopant concentration. In all the samples, only ZnO and CuO phases were detected, aiding the ascertainment of any ferromagnetic response from the samples as arising from the formation of a true dilute magnetic semiconductor.

A catalyst free, structure-induced heterogeneous nucleation and direct growth of ZnO nanowires on organic and inorganic substrates was prepared by low-temperature solution approach process. The experimental results showed that ZnO nanowires could be directly synthesized upon the concave of substrate without any pre-seeding. In this work ZnO nanowires were grown on both polystyrene bead layer and physical-grinded wafer substrate. ZnO nanowires with a broad aspect ratio of 10−2 ∼ 102 was controlled mainly by adjusting of reactant concentration and pH state of solution. A needle-like ZnO nanotip were also prepared by a two-step limited growth condition as a result that tip diameter is several nanometers only, which may be highly in favor of the field emission. Structure-induced heterogeneous nucleation and growth facilitates the fabrication of ZnO nanowires as the potential photoeletronic units in field-emission displays.

Self-assembled GaInNAs/GaAsN single layer quantum dot (QD) lasers grown using solid source molecular beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. High-temperature operation up to 65°C was demonstrated from an unbonded GaInNAs QD laser (50 × 1060 μm2), with high characteristic temperature (T0) of 79.4 K in the temperature range of 10-60°C. For comparison, temperature-dependent operation has also been studied on the GaInNAs single quantum well (SQW) lasers. Unlike the relation between the cavity length and T0 in GaInNAs SQW lasers, longer-cavity GaInNAs QD laser (50 × 1700 μm2) showed lower T0 of 65.1 K, which is presumably believed due to the nonuniformity of the GaInNAs QD layer.