ZnSe–Si Bi‐coaxial Nanowire Heterostructures

We report on the fabrication, structural characterization, and luminescence properties of ZnSe/Si bi‐coaxial nanowire heterostructures. Uniform ZnSe/Si bi‐coaxial nanowire heterostructures are grown on silicon substrates by the simple one‐step thermal evaporation of ZnSe powder in the presence of hydrogen. Both ZnSe and silicon are single‐crystalline in the bi‐coaxial nanowire heterostructures, and there is a sharp interface along the nanowire axial direction. Furthermore, secondary nanostructures of either ZnSe nanobrushes or a SiO_x sheath are also grown on the primary bi‐coaxial nanowires, depending on the ratio of the source materials. The experimental evidence strongly suggests that bi‐coaxial nanowires are formed via a co‐growth mechanism, that is, ZnSe terminates specific surfaces of silicon and leads to anisotropic, one‐dimensional silicon growth, which simultaneously serves as preferential nucleation sites for ZnSe, resulting in the bi‐coaxial nanowire heterostructures. In addition, the optical properties of ZnSe/Si nanowires are investigated using low‐temperature photoluminescence spectroscopy.     

Electrical,optical, and structural properties of thin films with tri-layers of AZO/ZnMgO/AZO grown by filtered vacuum arc deposition

Transparent conductive oxides (TCO) are indispensable as front electrode for most of thin film electronic devices such as transparent electrodes for flat panel displays, photovoltaic cells, windshield defrosters, transparent thin film transistors, and low emissivity windows. Thin films of aluminum-doped zinc oxide (AZO) have shown to be one of the most promising TCOs. In this study, three layered Al-doped ZnO (AZO)/ZnMgO/AZO heterostructures were prepared by filtered cathodic arc deposition (FCAD) on glass substrates. The objective is to find a set of parameters that will allow for improved optical and electrical properties of the films such as low resistivity, high mobility, high number of charge carriers, and high transmittance. We have investigated the effect of modifications in thickness and doping of the ZnMgO inner layer on the structural, electrical, and optical characteristics of the stacked heterostructures.     

Piezoreflectance characterization of resonant tunneling and modulation-doped heterostructures

We used piezoreflectance, a stress modulation technique, to optically characterize both double-barrier resonant tunneling structures and modulation-doped heterostructures. This technique easily probed the single quantum wells buried below the ∼0.5-μm-thick n⁺ GaAs surface layers required for ohmic contacts. In fact, the positions of salient piezoreflectance spectral features denoted subtle variations of well width and barrier height and width; lineshapes indicated interface roughness. Since piezoreflectance spectra of our modulation-doped samples had sharp features associated with quantum confinement, and the corresponding photoreflectence spectra had Franz-Keldysh oscillations that depended on the built-in electric field, we could calculate energy levels that reflected not only growth parameters but experimentally determined potential profiles as well. Moreover, the sensitivity of piezoreflectance to carbon and silicon acceptor states permitted us to assess the material quality.     

Luminescence and lasing in GaN epitaxial layers and InGaN/GaN quantum well heterostructures under optical and electron-beam excitation

Interrelation between stimulated and excitonic emission intensity of GaN epitaxial layers and yellow luminescence intensity as well as correlation between photoluminescence and laser properties of InGaN based multiple quantum well heterostructures was investigated. It was found among all studied undoped GaN epitaxial layers that the higher intensity of the yellow luminescence and so the higher concentration of the yellow luminescence related centres the higher is the excitonic, electron–hole plasma and stimulated emission intensity. It was shown that a small Stokes shift and a high ratio of the luminescence intensity from InGaN quantum well layers to the photoluminescence intensity from GaN barrier layers indicate high laser quality of the multiple quantum well heterostructures. The lowest full width at half maximum of the laser line was 0.04 nm, the highest operating temperature was 585 K, the lowest threshold was 100 kW cm⁻², the highest characteristic temperature was 164 K and the highest wavelength was 442.5 nm. The far-field patterns of the laser emission from the MQW lasers consist of two approximately symmetrical high brightness spots localized at angles =±30–35°.     

Science and technology of ferroelectric films and heterostructures for non-volatile ferroelectric memories

We present in this article a review of the status of thin film ferroelectric materials for nonvolatile memories. Key materials issues relevant to the integration of these materials on Si wafers are discussed. The effect of film microstructure and electrode defect chemistry on the ferroelectric properties relevant to a high density nonvolatile memory technology are discussed. The second part of this review focuses on approaches to integrate these capacitor structures on a filled poly-Si plug which is a critical requirement for a high density memory technology. Finally, the use of novel surface probes to study and understand broadband polarization dynamics in ferroelectric thin films is also presented.     

The growth and characterization of device quality InP/ Ga1-xinxasyp1-y double heterostructures by atmospheric-pressure MOVPE using trimethylindium

We report on recent developments of the atmospheric pressure OMVPE of InP and In_xGa_1-xAS_yP_1-y using trimethylindium, trimethylgallium, phosphine and arsine. The use of diffuser organometallic sources significantly increased the accuracy of quaternary composition control. This control was achieved in the whole range of quaternary light emitting wavelengths from 1.20 micrometers up to the ternary GaInAs limit. The influence of the carrier gas was further investigated: device-quality heterostructures were obtained for either of the three carrier gases hydrogen, helium and argon. The experimental conditions for growing quaternaries with a given composition agree well with a simple model. This work has permitted the realization of 1.3 micrometer laser heterostructures with low threshold current density. This work was partially presented at the 1985 Electron Materials Conference, Boulder (Colo. USA), June 1985.     

A new LPE growth method of semiconductor heterostructures with thickness profile variation of epitaxial layers

We have investigated and developed a method for the LPE growth of layers with approximately parabolic cross section. The channels were created during the growth process by modulating the liquid phase thickness with W or Mo wires parallel to the substrate. The main parameters of the channel can be controlled by changing the wire’s diameter and its distance from the substrate. This method can be incorporated directly into the growth process of a laser structure with an unstable resonator without the need of additional treatments as chemical etching, to produce the channel structure.     

Indirect band gaps in quantum dots made from direct-gap bulk materials

The conditions under which the band gaps of free standing and embedded semiconductor quantum dots are direct or indirect are discussed. Semiconductor quantum dots are classified into three categories; (i) free standing dots, (ii) dots embedded in a direct gap matrix, and (iii) dots embedded in an indirect gap matrix. For each category, qualitative predictions are first discussed, followed by the results of both recent experiments and state of the art pseudopotential calculations. We show that:

Fabrication of CdS/SnS heterostructured device using successive ionic layer adsorption and reaction deposited SnS

In the present work successive ionic layer adsorption and reaction (SILAR) method has been employed for the growth of SnS films on chemical bath deposited CdS thin films. The as-grown and post annealed CdS/SnS heterostructures were investigated under dark and illuminated conditions. It has been observed that annealing improves the quality of the device. This paper presents the attempt towards realizing SnS based heterostructured devices using SnS films grown by SILAR technique.