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The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etched stripe-patterned substrates were investigated. Footprint-like patterns, located directly above the inclined groove sidewalls, were found on the as-grown LED surface. Cross-sectional transmission electron microscopy (TEM) showed that ‘tumor’-like structures with poor crystal quality were initiated on the inclined sidewalls, seeding dislocation bundles in the subsequently grown crystal. The high dislocation density slowed down the growth above the inclined sidewall, resulting in the uneven morphology. The fabricated devices showed over 30% enhancement in light output power as a result of improvements in both internal and extraction efficiencies.

We studied electrodeless photoelectrochemical (ELPEC) etching of GaN in a K2S2O8/KOH solution irradiated either continuously or periodically with ultraviolet (UV) light. The rate of recombination of electrons and holes at dislocation defects is greater than for crystalline GaN. The ELPEC etching with a continuous UV light resulted in a selective etching between dislocations and crystalline GaN and a rough etched surface. To reduce the recombination of the photo-generated carriers, the GaN was irradiated with periodical UV light modulated by a chopper during ELPEC etching. The shorter the interval of UV irradiation, the smoother is the etched GaN surface. A uniform and smooth etched surface was obtained with a root-mean-square (RMS) roughness 0.37 nm in solution (0.01 M KOH, 0.05 M K2S2O8) with a chopper frequency 2500 Hz. The p-GaN etching was also realized by ELPEC etching with a chopped UV source (ELPEC-CS etching) using an Au mask in K2S2O8/KOH solution. The etching rate of p-GaN was 2.8 nm/min at a chopper frequency of 3000 Hz and a power intensity of 63 mW/cm−2 in solution (0.5 M KOH, 0.05 M K2S2O8).

Damage-free etching of GaN by Cl2, assisted by an ArF (193 nrm) excimer laser, is demonstrated. At low temperatures, photo-assisted etching can provide a better etch rate and largely improve the surface morphology and quality. AFM results show that the etched GaN surface is obtained with a root-mean-square roughness of 1.7 nm. As compared with the photoluminescence spectra of photoelectrochemical wet etched GaN, the photo-assisted cryogenic etching is proved to be a damage-free dry etching technique.

The intrinsic response of quantum dash lasers are measured using a pulse optical modulation technique. Our results show fast well-to-dash carrier capture and intra-dash carrier relaxation with K-factors independent on the pump wavelengths.

We demonstrate bandgap tuned InAs/InAlGaAs quantum-dash-in-well lasers grown on InP material using postgrowth quantum heterostructure intermixing. Compared to the control (non-intermixed) lasers, the light-current characteristics of lasers with emission wavelength tuned by over 100 nm shows insignificant changed suggesting that the quality of the intermixed material is well-preserved.

Three LOCOS-type isolations, viz. modified Scaled LOCOS (MSL), Sidewall Sealed MSL (SSMSL), and Recessed SSMSL (RSSMSL) are evaluated for the 0.6 /spl mu/m-pitch isolation of 256 Mbit DRAM. About 4000 /spl Aring/ field oxide grown in a 1100/spl deg/C wet ambient is found to be optimal for field oxide thinning and bird's beak "punch-through" effects. At a given pad oxide thickness of 100 /spl Aring/ the end-of-line encroachment is the largest for MSL isolation, which essentially rules out MSL as a possible candidate. Although both SSMSL and RSSMSL have similarly good isolation characteristics and diode leakages, only RSSMSL has the undesirable subthreshold double-hump effect and reduced gate oxide integrity, both of which are due to the sharp corners associated with the silicon recess etch of the RSSMSL structure. Therefore, for the three structure studied, only SSMSL is a viable candidate for the 0.6 /spl mu/m-pitch isolation of 256 Mbit DRAM.

The design, fabrication, and characteristics of a 350-V, 100-A buried-gate static induction transistor (SIT) as a power switching device for applications in military and space environments because of its potential for radiation hardness, high-frequency operation, and the incorporation of on-chip smart power sensor and logic functions are described. The potential radiation hardness of this class of devices was evaluated by measurement of SIT characteristics after irradiation with 100-Mrad (2-MeV) electrons and up to 10/sup 16/ fission neutrons/cm/sup 2/. High-temperature operation and the possibility of radiation damage self-annealing are discussed. >

The measured short-circuit current density in bifacial dendritic web silicon solar cells has been found to decrease with decreasing base resistivity, particularly under back illumination. In addition, the ratio of short-circuit current under back illumination to short-circuit current under front illumination was observed to vary with light intensity. These observations reflect the fact that the minority-carrier lifetime in the base of these cells is a function of the base resistivity and the illumination level. The dopant was assumed to play only an indirect role in determining lifetime. This decrease in lifetime is shown to follow from a distribution of defect levels in the bandgap. These levels are a consequence of extended defects that have been observed in the web material, namely oxide precipitates and the dislocation cores that they decorate. The dopant, acts only in the indirect role of moving the Fermi level over an existing background distribution of defect levels that arise from the extended defects. Assuming a parabolic distribution of defect levels in the bandgap, the minority-carrier lifetime was calculated as a function of doping density and excess carrier concentration (illumination level) using the Shockley-Reed-Hall theory. The short-circuit current densities that were calculated using these lifetimes agreed reasonably well with measured values for bifacial dendritic web silicon solar cells. The measurements were made over a range of doping densities (6*10/sup 14/ to 3*10/sup 16/ cm/sup -3/) and illumination levels (0.001 to 1 sun) for both front and back illumination of the bifacial cells. >

In ionizing-radiation environments, oxide charge buildup in the buried oxide of SIMOX SOI material causes an increase in the back-channel leakage current, resulting in an instability in electronic circuits formed on SIMOX wafers. We report the measured distributions of radiation-induced oxide charge density in buried oxides formed by oxygen implantation. These are obtained by etch-back experiments including C-V measurements using a mercury probe and ellipsometer measurements. The results show a region of higher charge density about 1500A from the top interface with a lower density region within a few hundred angstroms of the top interface. The results also show that the oxide charge density decreases with annealing temperature. Some unusual optical properties of SIMOX oxide observed in ellipsometer measurements are discussed comparatively with thermal oxide.