The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

An improved human user computer interface system, wherein a user characteristic or set of characteristics, such as demographic profile or societal “role”, is employed to define a scope or domain of operation. The operation itself may be a database search, to interactively define a taxonomic context for the operation, a business negotiation, or other activity. After retrieval of results, a scoring or ranking may be applied according to user define criteria, which are, for example, commensurate with the relevance to the context, but may be, for example, by date, source, or other secondary criteria. A user profile is preferably stored in a computer accessible form, and may be used to provide a history of use, persistent customization, collaborative filtering and demographic information for the user. Advantageously, user privacy and anonymity is maintained by physical and algorithmic controls over access to the personal profiles, and releasing only aggregate data without personally identifying information or of small groups.

Database access system

The systems and methods described herein relate to LED systems capable of generating light, such as for illumination or display purposes. The light-emitting LEDs may be controlled by a processor to alter the brightness and/or color of the generated light, e.g., by using pulse-width modulated signals. Thus, the resulting illumination may be controlled by a computer program to provide complex, predesigned patterns of light in virtually any environment.

Multicolored led lighting method and apparatus

Light emitting displays and lamps are produced by photo pumping UV excitable phosphors with UV emitting GaN-based light emitting diodes (LEDs). Resonant cavities are incorporated into the LED structures to both narrow and heighten the emission spectrum. Color displays are produced from arrays of individual LED-phosphor combinations of different colors. Such LED pumped phosphor devices do not require a vacuum environment and operate at much lower voltages than the electron beam pumped phosphor screens of cathode ray tubes (CRTs).

Visible light emitting devices including uv-light emitting diode and uv-excitable, visible light emitting phosphor, and method of producing such devices

Using infrared and Raman spectroscopy, we have observed two local vibrational modes related to H bonded to N acceptors in ZnSe samples grown by metalorganic vapor phase epitaxy. We assign the new mode seen at 3194 cm−1 to a N—H stretching vibrational mode and tentatively assign the mode found at 783 cm−1 to a N—H wagging vibrational mode. Polarized Raman spectroscopy was used to determine that the symmetry of the defect complex is C3 v, which implies that the H atom is in either a bonding or antibonding position.

Local vibrational mode spectroscopy of nitrogen‐hydrogen complex in ZnSe

Light efficient packaging configurations for LED lamps using high refractive index encapsulants. The packaging configurations including dome (bullet) shaped LED's, SMD (surface mount device) LED's and a hybrid LED type, including a dome mounted within a SMD package. The packaging configurations increase the LED's light emission efficiency at a reasonable cost and in a commercially viable manner, by maximizing the light efficiency while minimizing the amount of high refractive index encapsulant used.

Light efficient packaging configurations for LED lamps using high refractive index encapsulants

We report a novel technique to obtain p‐type ZnSe layers doped with nitrogen. The layers were grown in a low‐pressure metalorganic vapor phase epitaxy system using ammonia as the dopant source. A rapid thermal anneal was used to enhance the activation of the nitrogen acceptors. Net acceptor concentration values as high as 3×1016/cm3 were obtained from capacitance‐voltage measurements and the profile was uniform over the thickness of the epitaxial layers. The 7 K photoluminescence spectrum was dominated by the acceptor bound exciton peak; the donor‐acceptor pair spectra were also observed.

Novel technique for p‐type nitrogen doped ZnSe epitaxial layers

When an atomic impurity is incorporated in a nanoparticle of size 2 to 10 nm, the quantum-confinement provided by the dielectric-boundary of the host-nanoparticle modulates the properties of the atom. This Quantum Confined Atom (QCA) shows extraordinary changes in its luminescent properties and is associated with the modulation of the excited states of the caged atom. These “atomically engineered nanomaterials,” pioneered and developed by Nanocrystals Technology, yield several novel properties and are expected to be a major contributor to the future of nanotechnology. Efficient QCA-Nanophosphors that emit different colors depending on the specific choice of the 'caged atom' are being developed for applications to solid-state lighting. We have made two key contributions to development of SSL. (1) By embedding nanoparticles in the encapsulant, the refractive index is enhanced to 1.8 that allows us to enhance Light Extraction Efficiency (LEE) of the LED chip. (2) Incorporation of appropriate nanophosphors enables efficient down-conversion with high color-quality. The combination of an optically transparent downconverter and high refractive index in an encapsulant has yielded Phosphor-Converted LEDs (PC-LEDs) that yield higher package optical efficiency at lower package-level cost. The LEE and wall plug efficiency enhancement due to the HRI encapsulant is applicable across the entire visible spectrum of monochromatic HB-LED lamps.

Quantum-confined-atom-based nanophosphors for solid state lighting

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