COMMAD 2000 Proceedings. Conference on Optoelectronic and Microelectronic Materials and Devices

We have studied the influence of hydrogen plasma treatment and annealing on GaN mms grown by plasma-assisted metal organic chemical vapor deposition (MOCVD). The X-ray diffraction (XRD) pattern of GaN films grown without assistance of hydrogen plasma show misoriented polycrystalline structure, while those grown with the assistance of hydrogen plasma show a crystalline structure with (0001) orientation. Post-growth hydrogenation and annealing reduces the carrier concentration of fUms grown without hydrogen plasma, but does not give a significant effect for mms grown with the assistance of a hydrogen plasma.

High power (265 mW) kink free operation of 4 /spl mu/m wide stripe devices is demonstrated for a 970 nm InGaAs/GaAs/AlGaAs asymmetric structure in CW conditions. The maximum of the optical field distribution is moved towards the n-side of the structure. The structure was designed to allow a higher value of the catastrophic optical damage of the mirror (COD). For devices having uncoated mirrors the COD level is 200 mW / facet. The kink free operation is limited by thermal waveguiding. The same devices operate kink free until 500 mA if operated in pulsed conditions: 1.75 /spl mu/s pulse width / 36 /spl mu/s between pulses.

Misfit stress in MBE grown heterostructures causes these structures to bend. Former theories on semiconductor wafer curvature have been re-examined and errors that have persisted in the literature have been corrected. We present an approach to describe the wafer curvature of strained layer systems using basic physical equations. A description of the position of the neutral plane for epitaxial heterostructures is presented. Wafer curvature has been studied using X-ray diffraction and the results are in good agreement with the theory.

Solid-state thermionic cooling has gained attention recently because of its potential high cooling power. Thermionic devices based on semiconductor heterostructures utilize the band-edge offset at a heterojunction as the thermionic emission potential barrier and a thin layer to separate the cold and hot junction. In this paper, we present the behavior of thermionic coolers with periodic barriers using gallium arsenide/aluminium gallium arsenide (GaAs/Al/sub x/Ga/sub 1-x/As) semiconductor heterostructures. The exact numerical calculation to model the device performance has shown that the thermal efficiency in a multilayer structure is optimised when the effect of phonon scattering is introduced in the model. Besides, the thermal efficiency depends critically on applied bias.

We describe a simple method based on photoluminescence, which allowed us to determine the absorption spectra of InAs/InAlAs quantum dots at low temperatures. The method is convenient when other, more conventional absorption measurements are not feasible, and the sample emits luminescence.

Binary TiO/sub 2/-Ga/sub 2/O/sub 3/ thin films were prepared from the sol-gel process. Titanium butoxide and gallium isopropoxide were used as precursor materials. The mixed solution was spun onto the sapphire and silicon substrates at 2500 rpm for 30 s to prepare thin films. The X-Ray Diffraction (XRD) results revealed that the films annealed at a temperature of 500/spl deg/C for 1 hr is /spl gamma/-Ga/sub 2/O/sub 3/ structure. Scanning Electronic Microscope (SEM) images revealed that the film surface is smooth with grains in a nanometer scale. The film showed good responses to 100 ppm, 1000 ppm and 1% O/sub 2/ at an operating temperature of 470/spl deg/C. The resistance of Ga-doped TiO/sub 2/ film is between the resistances of pure TiO/sub 2/ and Ga/sub 2/O/sub 3/ films. The response of Ga-doped TiO/sub 2/ thin film is sensitive, fast and stable to oxygen gas.

p/sup ++/-GaAs/n-InGaP heterojunction field-effect transistors (HJFETs) with a highly carbon-doped gate and a wide-gap channel were reported. A self-aligned T-shaped gate HJFET exhibits a gate of 0.6 /spl mu/m in length by depositing gate metal of 1.0 /spl mu/m. DC characteristics including a turn-on voltage of 2.0 V at 1 mA/mm, a gate-drain breakdown voltage up to 30 V, a drain-source breakdown voltage exceeding 25 V, a maximum available transconductance of 160 mS/mm and AC performances such as a unit-current gain frequency of 16.8 GHz, and a unit-power gain frequency of 25 GHz were obtained for a non self-aligned HJFET. With a self-aligned processing structure, the transconductance and f/sub max/ were improved to 230 mS/mm and 35 GHz, respectively.

In this paper, the frequency response limited by avalanche buildup time was calculated using a realistic model which reflects a zinc diffusion profile and includes a nonlocal multiplication theory. The dependency of a chip capacitance on the floating guard rings was also investigated. The trade-off relation between the edge gain suppression and the chip capacitance is addressed.

The role of interstitial (mobile) hydrogen in the creation of structural defects in doped hydrogenated amorphous silicon (a-Si:H) is elucidated by first reviewing recent calculations of their electronic states. Two new processes involving hydrogen interstitials are proposed. In the first, a neutral hydrogen atom reacts with a dopant atom to produce a charged dopant-interstitial pair. In the other process, suggested by Muon Spin Resonance (MuSR) experiments, neutral hydrogen diffuses to charged silicon dangling bonds, where charge transfer occurs between the two species. These two chemical processes are then put together to show how dopants may produce charged defects in a-Si:H.

The sol-gel route to thin bimetallic oxide sensor films was studied in terms of the evolution of a viscoelastic Ti gel precursor containing occluded Cr. The influence of Cr:Ti atomic ratio and annealing temperature was related to the resultant microstructure, morphology and oxygen sensing response of the annealed thin films. It was shown that progressive increase in Cr content changed the Ti-O properties from a n-type to a p-type semiconductor film with a commensurate reversal in sensor response.