Pseudomorphic GaAs1-xSbx quantum-well (QW) structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD) have been studied with various barrier materials to investigate the energy band lineup. To determine the band lineup of these structures, we have performed low-temperature current-dependent cathodoluminescence (LT-CL) measurements at 10K. For the structure with GaAs barriers, the data show strong evidence of Type-II staggered band lineup, which means that holes are confined in the valence band heavy-hole level of the GaAs1-xSbx quantum well and electrons are confined in the conduction band of the GaAs barrier.

For the InGaP barriers, however, we observed only one peak that is related to transitions of a Type-I band lineup. From the LT-CL results, we find that the valence-band discontinuity ratio (Qv) between the GaAs0.73Sb0.27 double quantum wells (DQWs) and the GaAs barriers is ∼1.20. Furthermore, to improve the carrier confinement, we propose that InGaP barriers provide a Type-I band lineup with the GaAsSb QW.

We have studied the effects of hydrogen plasma treatment on the defect characteristics in single crystal ZnO grown at Eagle-Picher by chemical vapor transport. Depth-dependent cathodoluminescence (CL) spectra, temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence (PL) spectra reveal significant changes resulting from unannealed exposure of n-type ZnO to a remote hydrogen plasma. Low temperature PL spectra show that this hydrogen exposure effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a new peak feature at 3.366 eV possibly related to a neutral donor bound exciton. A simple thermal analysis of the activation energy for the 3.366 eV line yields 5–10 meV. Hydrogenation also produces a violet 100 meV-wide peak centered at 3.16 eV. Remote plasma hydrogenation produces similar changes in room-temperature CL spectra: near-band edge emission intensity increases with hydrogenation. Furthermore, this new emission increases with proximity to the free ZnO surfaces, i.e., with decreasing the energy of the incident electron beam from 3.0 down to 0.5 keV. Subsequent annealing at 450 °C completely restores both the PL and CL spectra in the sub-band gap range. The appearance of a new bound-exciton feature at 3.366 eV with H plasma exposure, the near-surface nature of the spectral changes, and the reversibility of spectral features with annealing indicate a direct link between H indiffusion and appearance of a shallow donor.

The microstructure of epitaxial InAs thin films grown by MOCVD on mask-patterned “LEO” (lateral epitaxial overgrowth) GaAs and on unpatterned GaAs substrates was studied using double-crystal x-ray diffraction, scanning electron microscopy and cross-sectional transmission electron microscopy. This paper describes the improvement in crystal quality (factor of 20 reduction in x-ray rocking curve width), the order of magnitude reduction in dislocation density, and the rearrangement of the remaining extended defects that were observed in the LEO material when compared to the film grown on the unpatterned wafer.

Alloyed metal contacts to <100> and <111> p-type silicon (Si) were investigated using doped self-aligning metallization techniques [1]. The contact allows the formation of a pn-junction and provides metallization for photovoltaic applications via thick film technology [2]. A formulated screen-printable thick film was annealed above Ag/Si eutectic temperature of 830°C. The annealing process resulted in a junction depth of 0.3–1.2 μm and improved adhesion by the reduction of native oxide layer through use of a wetting agent. The technique inhibits shunts (high conductivity paths through the solar cell pn-junction caused by excessive metallization penetration). The technique also reduces the interfacial resistance due to dissimilar materials in contact – a parasitic resistance that also limit solar cell performance. The use of metallic Mg as a wetting agent additive in the thick film silver matrix was explored. Studies were carried out on screen printable thick films and the reducing effects of Mg were investigated using both air and reducing atmosphere (H2) annealing furnaces. We observed a correlation between increased alloying with reduced series resistance.

We present a far-infrared spectroscopic ellipsometry study of the phonon properties of partially CuPtB -ordered (AlxGa1-x)0.52In0.48P with x =0, 0.32, 0.7, and 1.0 and degrees of ordering η = 0 … 0.63, determined from generalized ellipsometry measurement of the near-band-gap order birefringence. An anharmonic oscillator approach is used to model the ordinary and extraordinary dielectric functions and determine the infrared-active longitudinal and transversal phonon modes of the thin film samples. Besides the isotropic GaP-, InP- and AlP-like phonon modes, we observe alloy-induced modes with low polarity for η ∼ 0. The evolution of lattice like and alloy-induced modes with increasing η is reviewed for Ga0.52In0.48P. With increasing η all phonon modes split in E- and A1 -type vibrations with polarization perpendicular and parallel to the sublattice ordering direction, respectively, and the mode frequencies shift continuously. Our observations extend recently published phonon frequencies from experiment and theory for CuPt-ordered Ga0.52In0.48P, which are compared and discussed. The phonon modes of highly ordered (AlxGa1-x)0.52In0.48P, η ∼ 0.6, are compared to the modes observed in the highly disordered quaternary solid solution. We propose the far-infrared dielectric anisotropy as a sensitive measure for sublattice ordering in multinary III-V alloys.

The formation of highly resistive films of single-crystal ZnO as a result of irradiation with MeV Li, O, and Si ions is demonstrated. Results show that the ion doses necessary for electrical isolation close-to-inversely depend on the number of ion-beam-generated atomic displacements. Results show that an increase in the dose of 2 MeV O ions (up to ∼ 2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼ 300 — 400 °C. For the case of multiple-energy implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Based on these results, the mechanism for electrical isolation in ZnO by ion bombardment is discussed.

Amorphous-microcrystalline Si has been grown with hydrogen dilution using the DC saddle-field glow-discharge deposition technique. The five-electrode saddle-field system allows for independent control of the discharge parameters and of the substrate bias. The film structure was studied using Raman spectroscopy and SEM. We find that the structure of the films depends mainly on hydrogen dilution, substrate bias, electrical conductivity of the substrate, and chamber pressure. The deposition conditions, which promote growth of microcrystals, have been identified. It was found that the local electric field at the substrate surface plays a key role in obtaining microcrystallinity.

Photoluminescence (PL) spectra of interband transitions in GaInNAs/GaAs single quantum wells grown by metalorganic chemical vapor deposition technique on semi-insulating GaAs substrates were measured at 77 K for several samples grown with different In composition and dimethylhydrazine (DMH)/III ratios. The results show that the PL intensity increases as the In mole fraction is increased from 0 to 25%, but the PL intensity is degraded for samples with an In mole fraction of 30% or higher. The peak position energies of the PL spectra were investigated as a function of the DMH/III ratio. Thermal annealing effect induced a blue-shift in the PL spectra peak position energy in samples grown with high DMH/III ratio.

The optical properties of SbBiI3 alloys have been investigated experimentally by absorption measurements and theoretically by a full-potential augmented plane wave (FPLAPW) method within the generalized gradient approximation. The fundamental band-gap energy of these alloys changes from BiI3- to SbI3-like with increasing percentage of Sb content. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results. We present calculated density-of-states as well as the dielectric functions for evaluation of future experiments.

The effect of single-step annealing under GPa hydrostatic pressures on the photoluminescence of Cz silicon samples has been investigated at 450, 650 and 1000°C. It has been demonstrated that the effect of applied pressure begins to be detectable at 650°C and significant at 1000°C, where not only the effect of the applied pressure but also that of the dopants was clearly evidenced. In the first case the presence of a gap level associated to self-interstitial clusters could be argued, while in the second case both the oxide segregation and the dislocation formation was shown to be enhanced by the pressure and selectively addressed to the type of doping, respectively.

In the bulk SrS has an indirect bandgap of ∼ 4.32 eV. When SrS is doped with tellurium, ultraviolet emission occurs at 360 nm (for singlet) and 400nm (for Te-Te dimers) due to recombination from bound exciton states. In this paper we discuss the ultraviolet emission of pulsed laser deposited thin films of SrS:Te grown at room temperature on Si. Deposited film thickness ranged from 0.1 – 1.5 mm, with optimized films grown at ∼0.5 mm to avoid peeling and cracking. Te doping was incorporated by both ion implantation and conventional diffusion of deposited Te capping films. The characteristics of the ultraviolet emission will be discussed along with results from microstructural, chemical and optical characterization techniques.

In this work, ZnO thin films were grown on amorphous fused silica and pre-oxidized silicon substrates by using pulsed laser deposition technique. X-ray diffraction patterns showed that the films were highly crystalline and c-axis oriented. The surface morphologies of the films were observed by using scanning electron microscope and optical microscope. Free exciton absorption was observed at room temperature for the film grown on fused silica substrate. The strong near-UV luminescence peaked at 380 nm were observed for all the films and was attributed to the phonon-related exciton emission. The effect of oxygen partial pressure on the luminescence intensity is also reported.

In order to fabricate good hetero-interface of GaAs/InGaP system by metal-organic vapor phase epitaxy (MOVPE), we studied the indium atom distribution by X-ray photoelectron spectroscopy (XPS). The systematic XPS depth profile analyses of InGaP/GaAs revealed that InGaP surface contains an excess amount of indium atoms. The excess indium atoms diffuse into GaAs layer and cause surface segregation. We have developed a novel gas switching sequence to switch the growth from InGaP to GaAs. That is, after the growth of InGaP, trimethylgallium (TMGa) was pre-introduced to the reactor to terminate the excess amount of indium atoms on InGaP layer. Then tertiarybutylarsine (TBAs) was allowed to flow on the InGaP surface to initiate GaAs growth. This new sequence reduced the amount of indium atoms at the interface and contributed to suppress the inter-diffusion and surface segregation of indium atoms.

InNAs/GaAs multiple-quantum-wells were grown by MOCVD on (100) SI-GaAs substrates using trimethylindium, tertiarybutylarsine, and 95–97.5% of dimethylhydrazine (DMHy) in the vapor phase. The crystalline quality and solid phase composition were evaluated using highresolution x-ray diffraction analysis. Nitrogen content in InNAs wells was determined to be 28%. Electron energy loss spectroscopy was used to confirm the presence of nitrogen in quantum wells. Surface morphology was investigated by atomic force microscopy (AFM) and field emission microscopy (FEM).

Radiation hardness on intersubband transition in proton-irradiated InGaAs/InAlAs multiple quantum wells is investigated using Fourier transform infrared absorption (FTIR) technique and compared to the results observed for the GaAs/AlGaAs multiple quantum wells. It is observed that the intersubband transition remains almost unchanged in samples irradiated with 1 MeV protons and with doses as high as 1×1014 cm-2. This dose on the other hand, was found to completely deplete the intersubband transition in GaAs/AlGaAs multiple quantum wells samples. The intersubband transition in InGaAs/InAlAs multiple quantum wells was almost washed out in samples irradiated with doses as high as 3×1015 cm-2. The partial thermal annealing recovery of the depleted intersubband transition in the proton irradiated InGaAs/InAlAs multiple quantum wells will be reported.

The presence of an internal strain arising from the GaAs/spin-on-glass (SOG)/Si bonding procedure was investigated. In addition, the magnitude of any residual stress at room temperature and the mechanisms that may impose a stress, leading to elastic or plastic deformation of the bonded GaAs films, were identified.

A comparative study of biaxial strain and stress, as a function of temperature in the range of 80- 300 K, in a bonded 2 μm-thick GaAs/SOG/Si sample and in an epitaxial 2 μm-thick GaAs/Si sample, grown by molecular beam epitaxy (MBE), will be presented. The type and magnitude of strain were determined by photoreflectance spectroscopy. In the case of GaAs/SOG/Si, the strain in the GaAs layer was found to be negligible, with compressive character, at room temperature and tensile in all other measured temperatures, whereas for the epitaxial GaAs/Si, the strain was taking significant tensile values in all temperatures. Furthermore, the strain for both samples was increasing with temperature reduction, as it is expected for a thermal strain induced by the different thermal expansion coefficients of GaAs and Si.

The comparative study indicated clearly that the bonded GaAs/SOG/Si films are essentially strain-free at room temperature. This is a very important result for the good reliability of laser diodes that can be processed from such bonded GaAs material, which also has a crystal quality similar to that of the available GaAs substrates.

In this work we report on the lattice site location of rare earths in single-crystalline ZnO by means of the emission channeling (EC) technique. Following low dose (3×1013at/cm2) 60 keV ion implantation of the precursor isotope 169Yb, a position-sensitive electron detector was used to monitor the angular distribution of the conversion electrons emitted from 169Tm* as a function of the annealing temperature up to 600°C in vacuum. An additional annealing at 800°C in flowing O2 was performed. The EC measurements revealed that around 95–100% of the rare earth atoms occupy substitutional Zn sites up to an annealing temperature of 600°C/vacuum. After the 800°C/O2 annealing, the emission channeling effects decreased considerably.

Iron disilicide shows great promise as a silicon based light emitter operating in the 1.3 to 1.5 μm wavelength range. However, there exists a number of questions related to the band structure and the ability to alloy and controllably dope the material both n and p type. In this paper we present Raman and magneto transport studies on β-FeSi2, β-(Fe1-xCrx)Si2, and β-(Fe1-xCox)Si2 grown by MBE. By comparing the spectra obtained for undoped and doped samples we provide a general overview of the effects of doping on the crystallinity of the material. The temperature dependent (4K<T<300K) magneto transport illustrates that Cr is a p-type dopant and Co is an n-type dopant in β-FeSi2.The temperature dependence of the resistivity indicates that the transport properties at higher temperatures are determined by free carriers whereas at lower temperatures impurity band conduction prevails.

Metastable defects are discovered in hydrogen-implanted n-type silicon. Hydrogen implantation was performed with the energy of 80 keV to a dose of 2×10 cm- at 109 K. After implantation, the sample temperature was raised to room temperature. DLTS measurements were carried out in the temperature range 80–290 K for fabricated diodes. When the sample is reverse-biased at 10V for 10 min at room temperature and then is cooled down to 80 K, three new peaks labeled EM1, EM2 and EM3 appear around 150, 190 and 240 K, respectively. The introduction of metastable defects is found to be characteristic of low temperature implantation. We have evaluated properties of EM1 in detail. EM1 with thermal emission activation energy of 0.29 eV has a peak in concentration around the depth of 0.64 μ m, which corresponds to the projected range of 80 keV hydrogen. EM1 is regenerated with the reverse bias applied around 270 K and is removed with the zero bias around 220 K.

Sources for low frequency noise in polycrystalline silicon thin-film transistors are analytically investigated. The grain boundary is modeled as symmetric Schottky barrier and a new device equation for current conduction in thin-film transistors is presented. At lower currents where barrier height is large enough to provide necessary distribution of time constants for 1/f noise, the number fluctuation via barrier height modulation at the grain boundary is found to be the main noise generation mechanism. At higher currents, mobility and diffusivity fluctuation are found to be dominant