We prepared β-FeSi2 thin-films by using a Pulsed Laser Deposition (PLD) method and succeeded to observe photoluminescence (PL) around 1.5 μm corresponding to β-FeSi2 band from the long-time and high-temperature annealed β-FeSi2 thin-films. The β-FeSi2 thin-films were ablated on Si(111) substrates heated at 550°C. After ablation, long-time and high-temperature thermal annealing was performed in order to improve the crystal-quality. Annealing times were 5, 10, 20 and 40 hrs, and annealing temperature was kept at 900 °C. Crystallinity was evaluated by an X-ray diffraction (XRD) measurement. We have observed eminent improvement on crystal-quality of β-FeSi2 thin-films. Annealed samples show (220) or (202) X-ray diffraction signals of β-FeSi2 and the full width at half maximum (FWHM) of these peaks were 0.27° although the thickness of the samples decreased with annealing time. Thermal-diffusion of Si atoms was observed from substrate to thin-films. Fe atoms in the ablated thin-films also diffused into the substrate. The relationship between the thickness of β-FeSi2 thin-films and the thermal-diffusion were investigated with rutherford backscattering (RBS) measurement. Maximum photoluminescence intensity around 1.5 μm was observed from the thickest β-FeSi2 thin-film with only 5 hrs annealing.

A microchip-sized InSb photodiode based infrared sensor (InSb PDS) that operates at room temperature was developed. The InSb PDS consists of 700 photodiodes connected in series and consumes no power, because it works in photovoltaic mode to output an open-circuit voltage. The InSb PDS has a typical responsivity of 1,900 V/W and an output noise of 0.15 μV/Hz1/2. A detectivity of 2.8×108 cmHz1/2/W was obtained at 300 K. The InSb PDS has performance high enough for applications such as mobile electronic equipment, personal computers, and consumer electronics

Dilute-nitrogen GaNAs epitaxial layers grown by metal-organic chemical vapor deposition were characterized by deep-level transient spectroscopy (DLTS). For all samples, the dominant DLTS signal corresponds to an electron trap having an activation energy of about 0.25 to 0.35 eV. The minority-carrier trap density in the p-type material is quantified based on computer simulation of the devices. The simulations show that only about 2% of the traps in the depleted layer are filled during the transient. The fraction of the traps that are filled depends strongly on the depth of the trap, but only weakly on the doping of the layers and on the conduction-band offset. The simulations provide a pathway to obtain semi-quantitative data for analysis of minority-carrier traps by DLTS.

We studied on effects of laser ablation on morphology of ZnO nanorods fabricated by low-pressure thermal chemical vapor deposition combined with laser ablation of Mn. In this paper, we studied on the effects of laser-ablation time period and energy density of laser beam at an initial stage of growth of ZnO nanorods. Both of laser ablation and chemical vapor deposition are started simultaneously and the laser ablation is stopped on the way of growth of ZnO nanorods. After the laser ablation is stopped, only chemical vapor deposition is continued. It is concluded from the experimental results that even if laser-ablation time period is only 30 sec and energy density of laser is only 0.023 Joule/cm2/pulse, the laser ablation shows remarkable effects on growth of ZnO nanorods.

We report on the material preparation and optical characterization of transition metal (Cr, Co) doped ternary cadmium chalcogenides for possible applications in mid-infrared (MIR) light source development. Cr2+ doped II-VI's (e.g. ZnSe, ZnS) have received significant attention for MIR solid-state laser development in the 2-3 μm region. Transition metal (TM) doped II-VI thin films are also currently being studied for the development of broadly tunable MIR sources pumped through electrical carrier-injection. In this paper, we present results of the material synthesis and IR spectroscopy of several Cr and Co doped cadmium chalcogenides including CdTe, CdMnTe, CdZnTe, CdMgTe, CdCaTe, and CdSrTe. Following the synthesis and purification of undoped II-VI materials, TM doping was achieved during in-situ Bridgman growth or through a thermal diffusion process. The Cr2+ doped II-VI materials were characterized by broad IR absorption bands centered at ∼1800–1900 nm and MIR emission extending from ∼2000–3500 nm. The emission lifetimes varied between 1-5 μs, depending on the Cr concentration and host composition. Co2+ doped cadmium chalcogenides exhibited several absorption bands in the infrared region and broad emission extending from ∼3-5 μm. Compared to Cr2+ doped II-VI's, the emission from Co2+ doped chalcogenides was significantly quenched at room-temperature due to the onset of non-radiative relaxations.

In this paper, we present GaAs/Ge heteroepitaxy grown by RIBER32 solid-source Molecular Beam Epitaxy (SSMBE) with initial GaAs nucleation by migration-enhanced epitaxy (MEE) technique. We look at the influence of substrate temperature during the MEE and the influence of Ge surface orientation to the quality of the GaAs layer. Three samples were grown for this study; the first two samples, sample A and B, have surface orientation of (100) 6° offcut towards (111) plane. This surface orientation was chosen as to achieve double-atomic steps surface that is crucial to suppress anti-phase domain (APD) formation. These samples were then subjected to different temperature during the MEE process, 450°C for sample A and 250°C for sample B. The third sample, sample C, has the same MEE substrate temperature as sample A, which is 450°C but with nominal (100) surface orientation. The growth conditions and structure of the layers after the MEE process were kept constant across the three samples.

We examine the structures and the optical quality of the samples by cross-sectional Transmission Electron Microscope (XTEM) and 5K photoluminescence (PL). Analyzing the XTEM images of sample A and B, it is found that the APD still appear in sample A while it is suppressed totally in sample B. It is also observed from sample A XTEM image that two APDs propagating with 45° and 135° angle, as measured from the GaAs/Ge interface, could meet with each other at certain layer thickness leading to self-annihilation. However, some of the self-annihilations took place only after the APDs propagated hundreds of nanometers in the GaAs layer, producing large undulation in the layer. As for sample B, we believe that the APD suppression is mainly due to the much lower nucleation temperature. At such low temperature, As dimers are adsorbed onto the substrate surface more readily with negligible re-evaporation. This ensures complete As coverage on the double-atomic steps Ge surface and minimize As vacancies that may act as defect initiation centers. Furthermore, the low substrate temperature shortens the migration distance of Ga adatoms, minimizing their adsorption into the kinks and step edges, resulting in two-dimensional growth mode instead of step-flow growth mode.

Meanwhile, XTEM image of sample C shows APDs that propagated almost perpendicularly to the GaAs/Ge interface, making it unlikely for the self-annihilation mechanism to take event. It is understood that the direction of propagation of the APD relies on the atomic steps reconstruction of the Ge starting surface. In the case of single atomic-step surface, the APDs propagate almost perpendicularly to the interface. Finally, the 5K PL spectra of the embedded InGaAs single quantum-well in all the samples clearly demonstrate that the best optical quality comes from sample B; which we believe mainly because of the total suppression of APD, leading to much improved layer quality.

The fabrication and properties of ZnO-based rectifying p-n and p-i-n junctions are reported. ZnO films with p-type conductivity were obtained by oxidation of ZnTe grown by MBE on GaAs substrate. Insulating and n-type ZnO films were deposited by magnetron sputtering. The processing of p-n junctions into device structures involved the formation of mesa geometry and preparation of ohmic contacts to p- and n-type regions.

Self-assembled InAs quantum dots (QDs) on GaAs substrate encapsulated with In0.15Ga0.85As1−xNx (GINA) have been grown by solid source molecular beam epitaxy, using optimal growth temperatures and rates for each of the two layers. The photoluminescence (PL) intensity increases for annealed samples. The optimum annealing temperature depends on the nitrogen composition. InAs QDs overgrown with larger nitrogen mole fraction GINA show a smaller PL peak blue-shift after annealing. Intense and narrow PL emission in the 1.5 µm range is achieved for samples annealed at optimal temperature.

GaAs1−xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 °C a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples.

For the heterogeneous integration of several layer structures for absorber, gain and passive waveguide sections in a monolithically-integrated mode locked laser diode, the bandgap of the absorber section has to be matched to the emission wavelength of the gain section. Because of the use of a multiple regrowth process for optical butt-coupling, the first grown multiple quantum-well gain material undergoes a quantum-well intermixing process, resulting in a blue shift of the emitting optical wavelength. Experimental results show, that the blue shift is dependent on the process details and cannot be investigated by simple thermal cycling of unprocessed quantum well-structures. With the introduction of an effective quantum-well width computed from the emission wavelength we found a linear relationship between the effective quantum well width shrinkage and the cumulated regrowth heating time of 8.3Å/h at a growth temperature of 630°C. Therefore knowing the cumulated regrowth time for a laser fabrication, we could successfully design the initial quantum well thickness that yields the targeted emitting wavelength and excellent matching to the absorber bandedge.

In this study, we have investigated the structure of nickel-cobalt silicide to understand its behavior at high temperature. Nickel-cobalt silicide was formed after two-step RTP at 500°C and 700°C respectively. We could observe by TEM that nickel-cobalt silicide consists of a structure which seems to be a Ni-Co-Si ternary phase. No nickel silicide phases and cobalt silicide phases were detected in nickel-cobalt silicide by XRD. From XPS depth profile, we could confirm that there is a cobalt composition gradient along the silicide.

A Lagrangian formulation for the valence bands of bulk zinc blende and wurtzite compound semiconductors provides a direct approach to determining derivative operator ordering at layer interfaces in the multiband k·P description of electronic states, in the envelope function approximation. The current continuity condition is obtained through a gauge-variation on the Lagrangian. The principle of least action together with the discretization of the action integral naturally leads into a finite element approach for the modeling and simulation of the multiband Schrödinger equations. Being a variational method, the wavefunctions and energy eigenvalues can be systematically improved with quadratic convergence. By including the Poisson Lagrangian, a self-consistent treatment of the Schrödinger-Poisson band-bending in arbitrarily doped structures is obtained. Numerical examples are presented for the valence band electronic states for quantum wells and superlattices. We have also coupled the finite element method with layer parameter optimizations to design heterostructures for lasers emitting at given wavelengths. It is in this sense that wavefunction engineering goes beyond the notion of bandgap engineering in providing the means for optimizing wavefunction localization in layers, selecting layer thicknesses, enhancing optical matrix elements, and laser gain.

We report growth and properties of GeSn and SiGeSn alloys on Si (100). These materials are prepared using a novel CVD approach based on reactions of Si-Ge hydrides and SnD4. High quality GeSn films with Sn contents up to 20%, and strain free microstructures have been obtained. The lattice mismatch between the films and Si is relieved by Lomer edge dislocations located at the interface. This material is of interest due to the predicted cross-over to a direct gap semiconductor for moderate Sn concentrations. We find that the direct band gap, and, consequently, the main absorption edge, shifts monotonically to lower energies as the Sn concentration is increased. The compositional dependence of the direct band gap shows a strong bowing, such that the direct band gap is reduced to 0.4 eV (from 0.8 eV for pure Ge) for a concentration of 14% Sn. The ternary SiGeSn alloy has been grown for the first time on GeSn buffer layers. This material opens up entirely new opportunities for strain and band gap engineering using group-IV materials via decoupling of strain and composition. Our SiGeSn layers have lattice constants above and below that of pure Ge, and depending on the thickness and composition of the underlying buffer layer they can be grown relaxed, with compressive, or with tensile strain. In addition to acting as a buffer layer for the growth of SiGeSn, we have found that GeSn can act as a template for the subsequent growth of a variety of materials, including III-V semiconductors.

Deep mesa etching and surface roughening have been implemented to InAs flip-chip LEDs emitting at 3300 nm (300 K). Near field and power measurements confirmed the output power enhancement of about 2 and brightness increase with and equivalent to a black body temperature of about 1250 K.

Si Plasma-enhanced chemical vapor deposition (PECVD) at a near-atmospheric pressure (NAP) of 500 Torr has been conducted by using a pulsed-electric-field based NAP-PECVD system. At a growth temperature of 180°C, poly-Si films with a high Raman ratio of 7.4 are obtained on glass substrates, while epitaxial-like growth occurs when Si(100) substrates are employed, as confirmed by Raman-scattering spectroscopy, X-ray diffraction, and a cross-sectional transmission-electron microscopy.

The effect of ammonium sulfide passivation on InAs/GaSb superlattice infrared detectors was investigated using two complementary techniques, namely, picosecond excitation correlation (PEC) measurement and variable-area diode array (VADA) surface recombination velocity (SRV) measurement. PEC measurements were conducted on etched InAs/GaSb superlattice mesas, which were passivated in aqueous ammonium sulfide solutions of various strengths for several durations. The PEC signal's decay time constant (DTC) is proportional to carrier lifetimes. At 77 K the PEC signal's DTC of the as-grown InAs/GaSb superlattice sample was 2.0 ns, while that of the unpassivated etched sample was reduced to 1.2 ns by the surface states at the mesa sidewalls. The most effective ammonium sulfide passivation process increased the PEC signal's DTC to 10.4 ns. However it is difficult to isolate surface recombination from other processes that contribute to the lifetime using the PEC data, therefore a VADA SRV measurement was undertaken to determine the effect of passivation on surface recombination. The obtained SRV in the depletion region of the InAs/GaSb superlattice and GaSb junction was 1.1×106 cm/s for the unpassivated sample and 4.6×105 cm/s for the passivated sample. At 77 K the highest R0A value measured in our passivated devices was 2540 W cm2 versus 0.22 W cm2 for the unpassivated diodes. The results of the lifetime, the SRV and the R0A measurements indicate that ammonium sulfide passivation will improve the performance of InAs/GaSb superlattice infrared detectors.

In this paper we report non magnetic elements (Al and Cu) doping effect on the structural and magneto-transport properties of Zn0.85Mn0.15O dilute magnetic semiconductors. Thin films of undoped Zn0.85Mn0.15O (ZnMnO), Al doped Zn0.80Al0.05Mn0.15O (ZnMnAlO), and Cu doped Zn0.85Cu0.05Mn0.15O (ZnMnCuO) were grown on sapphire single crystals using pulse laser deposition technique. X-Ray Diffraction and Raman Spectra confirm the epitaxial growth with a strong orientation along the c-axis. Scanning Electron Microscopy and Atomic Force Microscopy reveals surface microstructure of all the films. Magneto transport properties quantify the carrier concentrations and mobilities at room temperature in all the films.

We have fabricated GaAs/GaNAs and GaAs/GaNAs/InGaAs MQWs introduced into the intrinsic region of GaAs p-i-n solar cells by atomic H-assisted RF-molecular beam epitaxy. Compared to the more conventional GaAs/InGaAs MQW cells, GaAs/GaNAs/InGaAs MQW cells exhibited improved external quantum efficiencies in the low energy region. This is due to the extension of band edge into longer wavelengths as achieved by use of GaNAs materials.

In this paper, the effect of substrate on the domain structure growth and electrical and magnetic properties of epitaxial Mn-doped Zn0.8Mn0.15O (ZnMnO) thin films has been investigated. Epitaxial thin films of ZnMnO dilute magnetic semiconductors (DMS) were grown on various substrates such as single crystal sapphire, single crystal silicon, and quartz substrates using Pulsed Laser Deposition (PLD) technique . Structural, surface, magnetic, and optical properties have been observed on these films using X-Ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Raman spectroscopy. X-Ray Diffraction shows that films are highly epitaxial and c-axis oriented with some induced strain. AFM images show that film surface is smooth with RMS roughness of the order of 1-2 nm over 5*5sq.micron. Magnetic characteristic properties such as carrier concentration, mobility, and temperature dependent resistivity were also investigated. Carrier concentration decreases and mobility increases for both the films on silicon and quartz substrates when compared to film on sapphire.

An H-terminated-surface conductive layer of B-doped diamond on a (111) surface was used to fabricate a metal insulator semiconductor field effect transistor (MISFET) using CaF2, SiO2 or Al2O3 gate insulators and a Cu-metal stacked gate. For a CaF2 gate, the maximum measured drain current (Idmax) was 240 mA/mm and the maximum transconductance (gm) was 70 mS/mm, and the cut-off frequency of 4 GHz was obtained. For a SiO2 gate, Idmax and gm were 75 mA/mm and 24 mS/mm, respectively, and for an Al2O3 gate, these characteristics were 86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported DC and RF characteristics for a diamond homoepitaxial (111) MISFET.