We report progress in growing non-polar a-plane III-nitride films and heterostructures over a-plane 4H-SiC. a-plane SiC is more closely lattice-matched to a-plane GaN than is r-plane sapphire. Consequently, better structural quality a-plane nitride films may result over a-plane SiC substrates. By migration enhanced metalorganic chemical vapor deposition (MEMOCVD), an atomically smooth (1120)AlN layer with RMS roughness of 0.3nm was obtained. From the results of XRD, the structural defects in the AlN layer on SiC substrates were strongly reduced compared to those grown on r-plane sapphire. Also by applying our selective area lateral epitaxy (SALE) growth procedure, we achieved high structural and optical quality a-plane GaN films on 4H-SiC with RMS roughness only 0.4nm. Therefore, non-polar III-nitride films and heterostructures on SiC substrates are promising building blocks for realizing high performance polarization-free devices.

(1010) GaN wafers grown on (100) face of γ-LiAlO2 were studied using transmission electron microscopy. Despite good lattice matching in this heteroepitaxial system, high densities of planar structural defects in the form of stacking faults on the basal plane and networks of boundaries located on prism planes inclined to the layer/substrate interface were present in these GaN layers. In addition, significant numbers of threading dislocations were observed. High-resolution electron microscopy indicates that stacking faults present on the basal plane in these layers are of low-energy intrinsic I1 type. This is consistent with diffraction contrast experiments.

We report the growth of GaN films by RF-MBE on SiC, ZnO, and LiGaO2 substrates, without buffer layers. Structural and optical properties of the films were probed by AFM for surface morphology, XRD for crystalline structure, and PL for optical properties. The dependence of GaN layer quality on the substrates and their surface pre-treatment prior to growth was studied within a similar MBE growth parameter matrix for all samples.

With great attention now being given to the wide band gap materials for electronic and optoelectronic device applications, there is interest in using ion implantation to introduce dopants into selected regions of devices. Work on ion implantation into SiC and the III-V nitrides is reviewed, new device concepts are given, and recent results are presented. These include SiC implantations at elevated temperatures, a GaN sample implanted with Si having an electron mobility after annealing of 106 cm2/V-s, and a novel GaN np junction diode created by implantation.

Cubic SiC thin films have been grown by supersonic jet epitaxy of single molecular precursors on Si(100), Si(111) and Separation by IMplanted OXygen (SIMOX) silicon on insulator (SOI) substrates at temperatures in the range 780 - 1000 °C. Real-time, in situ optical reflectivity was used to monitor the film growth. Films were characterized by ellipsometry, x-ray diffraction (XRD), and transmission electron microscopy (TEM). Monocrystalline, crack-free epitaxial cubic SiC thin films were successfully grown at 830 °C on carbonized Si(111) substrates using supersonic molecular jets of dimethylisopropylsilane, (CH3)2CHSiH(CH3)2, and diethylmethylsilane, (CH3CH2)2SiHCH3. Highly oriented cubic SiC thin films in the [100] direction were obtained on SIMOX(100) at 900 °C with dimethylisopropylsilane and on Si(100) at 1000 °C with diethylmethylsilane. A carbonized Si(100) surface was found to enhance SiC deposition from diethylmethylsilane at a growth temperature of 950 °C.

Silicon multiple quantum wells confined by ZnS barriers have been grown by MOCVD. Calculations indicate that well widths must be less than 15Å for visible light emission, basically independent of the band offsets. No near-infrared photoluminescence (except bulk Si band-edge emission) was observed from samples with 70Å or greater Si layers, using stimulation at 325 nm with a He-Cd laser; hole trapping in ZnS may play a role. However, we found evidence of yellow light emission from samples which possibly contain Si quantum dots embedded in ZnS.

GaN was grown by supersonic jet epitaxy(SSJE), seeding triethylgallium in helium carrier gas. Activated nitrogen was supplied by a microwave plasma source. Single crystalline GaN films were deposited on the Si-face 6H-SiC and the c-plane sapphire substrates at 600–670°C. A cubic SiC buffer layer was grown onSi(111) at 800°C by SSJE using dichlorosilane, acetylene, and a high quality GaN crystal was grown on this template at 630°C. The materials high quality was proved by hard rectifying characteristics of a diode with an N-GaN/β-SiC/P-Si(111) structure.

Silicon multiquantum wells ranging in width from 3 to 15 nm were deposited on closely lattice-matched ZnS barriers. MOCVD was used to deposit the ZnS films using diethyl zinc and hydrogen sulfide as the precursors; disilane was used to deposit silicon layers at low temperatures. Single and multiple silicon nano-layers were observed by transmission electron microscopy and secondary ion mass spectrometry. Photoluminesence studies revealed emissions peaks which were blue-shifted with respect to the edge emission from bulk silicon substrates. The observation of emission from silicon nanostructures shifted to wavelengths as short as the 800-850 nm range is consistent with the effects of quantum confinement in silicon nanostructures.

We have investigated the application of ion implantation technique for introducing activator and co-activator ions into host materials such as ZnS and Zn2SiO4, and have produced phosphors with differing emission peaks throughout the visible range. A number of different ions including, Mn+, Al+ and rare-earth metals have been implanted. Zn2SiO4:Mn showed bright yellow cathodoluminescence. We have demonstrated that by varying the parameters for ion implantation and annealing, a single ZnS sample with emission peaks ranging from violet to yellow can be produced; i.e, chromaticity engineering. In one case, our results indicated that photoluminescence (PL) spectrum of ZnS phosphors shifts from blue to green by increasing the dose of implanted A+ ions. The Al+-implanted ZnS samples showed emission peaks shifting from 440 to 510 nm when the aluminum dose was raised from 1 × 1015 to 1 × 1017 A1+/cm2. Therefore, by activating color centers in thin film phosphors using ion implantation, efficient and low-cost full-color field emission displays can be fabricated on a single layer of host material.

We discuss the operation of porous silicon light-emitting diodes prepared as heterojunctions between n-type In2O3:Sn (ITO) and p-type silicon nanostructures, exhibiting quantum confinement effects. The transparent ITO affords light emission through the top surface of the device, as well as providing passivation and hence long term stability. We describe a model for the injection of minority carrier electrons into the porous silicon regions, which results in the emission of yellow-orange DC electroluminescence. A detailed study of the forward bias current-voltage characteristics of the devices will be given, which allows calculations of the densities of interface states. A tendency to pin the hole fermi energy near the neutral level, φ0, is shown to control the extraction of majority carriers. Methods for improving LED efficiency by alleviating a parasitic shunt current path through interface states will be addressed.