Henry W. White

Properties of arsenic-doped p-type ZnO grown by hybrid beam deposition

As-doped ZnO (ZnO:As) films have been characterized. ZnO:As films show p-type characteristics determined by Hall-effect and photoluminescence (PL) measurements. The hole concentration can be increased up to the mid-1017-cm−3 range. The thermal binding energy of the As acceptor (EAth-b) is 120±10 meV, as derived from temperature-dependent Hall-effect measurements. The PL spectra reveal two different acceptor levels (EAopt-b), located at 115 and 164 meV, respectively, above the maximum of the ZnO valence band, and also show the binding energy of the exciton to the As-acceptor (EAXb) is about 12 meV. The values of the ratio EAXb/(EAth-b or EAopt-b) are located in the range from 0.07 to 0.11.

Next generation of oxide photonic devices: ZnO-based ultraviolet light emitting diodes

Results are presented for ZnO-based ultraviolet light emitting diodes (LEDs) that employ a BeZnO∕ZnO active layer comprised of seven quantum wells. Arsenic and gallium are used for p-type and n-type layers. The ZnO-based LEDs show two dominant electroluminescence peaks located in the ultraviolet spectral region between 360 and 390nm, as well as a broad peak at 550nm.

Wide-band gap oxide alloy: BeZnO

A wide-band gap oxide alloy, BeZnO, is proposed and studied in this letter. The BeZnO films were deposited on sapphire substrates by our hybrid beam deposition growth method. The value of the energy band gap of BeZnO can be efficiently engineered to vary from the ZnO band gap (3.4 eV) to that of BeO (10.6 eV). BeZnO can be used for fabricating films and heterostructures of ZnO-based electronic and photonic devices and for other applications. Changes in the measured energy band gap and lattice constant values with Be content are described for BeZnO alloys.

Excitonic ultraviolet lasing in ZnO-based light emitting devices

The authors have fabricated ultraviolet (UV) laser diodes based on ZnO∕BeZnO films. The devices have p-n heterojunction structures with a multiple quantum well (MQW) active layer sandwiched between guide-confinement layers. The MQW active layer comprises undoped ZnO and BeZnO, while the two guide-confinement layers were As-doped p-type ZnO∕BeZnO and Ga-doped n-type BeZnO∕ZnO films, respectively. The exciton binding energy in the MQW region is exceptionally large (263meV). Exciton-related lasing was observed by optically pumping the MQWs. ZnO∕BeZnO-based diodes showed laser action by current injection at room temperature. The lasing mechanism is inelastic exciton-exciton collision.

ZnO devices: Photodiodes and p-type field-effect transistors

The potential use of ZnO-based photonic and electronic devices has been demonstrated by the fabrication of prototype ultraviolet (UV) photodetector and field-effect transistor (FET) devices that contain films of p-type ZnO with arsenic as the p-type dopant. These p-type films have high crystalline quality and show long-term stability. The ZnO UV photodetectors are based on p-n junctions. The FETs are made with metal-semiconductor Schottky contacts on p-type ZnO and are normally off (enhancement) devices. The spectral and electrical characteristics of these devices are presented and explained.

Fabrication of homostructural ZnO p–n junctions and ohmic contacts to arsenic-doped p-type ZnO

We report fabrication of homostructural ZnO p–n junctions that contain arsenic (As)-doped ZnO (ZnO:As) and intrinsic n-type ZnO layers. We also describe the metallization process for forming ohmic contacts to p-type ZnO. ZnO films were synthesized on n-type SiC substrates by hybrid beam deposition. Ni/Au metal contacts show linear I–V characteristics indicative of ohmic behavior, while other metal contacts (e.g., In/Au and Ti/Au) show nonlinear characteristics with rectification that reveal the presence of Schottky barriers. The characteristics for p–n junctions composed of ZnO layers are confirmed by I–V measurements.

A New Method for the Study of Adhesion: Application of Inelastic Electron Tunneling Spectroscopy

Abstract Inelastic electron tunneling spectroscopy provides an incredibly sensitive and versatile method of detecting and identifying molecular species adsorbed on the surface of a metal oxide. IETS spectra have been measured on the components of the commercial adhesive, Hercules 3501. This epoxy system consists of two molecular components; diamino diphenyl sulfone (DPS) and tetraglycidycl 4,4′ diamino diphenyl methane (DPM). IETS spectra of the individual components and of the epoxy mixture adsorbed on aluminum oxide have been obtained and the vibrational modes and frequencies assigned by comparison with computer calculations and existing infrared optical spectra. IETS is a useful tool for the study of molecular adhesion to an oxide. It is one of the most important methods available for determining the interface physics and chemistry of adhesive bondlines. Its usefulness is greatly enhanced by the fact that in situ studies can be made. Spectra have been obtained on the components and mixture of the high ...

Study of the corrosion of aluminum by CCl4 using inelastic electron tunneling spectroscopy

Inelastic electron tunneling spectroscopy (IETS) has been used to determine the molecular species which occur on an aluminum oxide surface during metallic corrosion by carbon tetrachloride. IETS spectra were obtained for CCl4 adsorbed on aluminum oxide and the observed vibration modes were assigned by comparison with infrared and Raman frequencies. Modes were observed which could be associated with the molecular species CCl4, AlCl, AlCl2, AlCl3, ⋅CCl3, C2Cl6, and the complex CCl+3[AlCl4]−. These species are those in the reaction sequence proposed by Stern and Uhlig for the corrosion of aluminum by CCl4. The results do not provide information on whether the reaction is chemical or electrochemical in nature. The fact that no modes were observed which would reflect oxygen–carbon bonding, and the presence of a large number of aluminum–chlorine modes suggest that the corrosion mechanism is by reaction of the solvent with exposed aluminum atoms.

Neutron irradiation and annealing of 10 B doped chemical vapor deposited diamond films

10B doped diamond films grown by hot filament chemical vapor deposition were neutron irradiated at moderately high fluence levels. The as-irradiated and annealed samples. along with an unirradiated sample, were analyzed using Raman spectroscopy and x-ray diffraction. It was found that a non-diamond amorphous phase was formed on irradiation. This phase transformed back to diamond on annealing. No graphite formation was observed. A comparison with nanodiamond powder was made. A similarity between irradiated diamond films and nanocrystalline diamond powder is discussed.

Study of the Molecule-metal Oxide Interface using Inelastic Electron Tunneling Spectroscopyt

Abstract Several examples in the application of inelastic electron tunneling spectroscopy (IETS) to study the molecular species which occur in adhesion, and in the corrosion and corrosion inhibition of aluminum in chlorinated hydrocarbons are reviewed. These examples illustrate some of the common aspects of the phenomena which occur at the metal oxide-organic interface in the areas of adhesion and corrosion. On a molecular level the concept of inhibition can be usefully applied to the areas of corrosion and adhesive failure.