Robert W. McClelland

A technique for producing epitaxial films on reuseable substrates

Using a new technique, which we have named the CLEFT process (cleavage of lateral epitaxial films for transfer), we have grown single‐crystal GaAs films by vapor phase epitaxy (VPE) on reusable GaAs substrates. A carbonized photoresist mask with narrow, widely spaced stripe openings is first deposited on a (110) GaAs substrate. Epitaxial growth initiated within the openings, followed by lateral growth over the mask, produces a continuous single‐crystal GaAs film. The upper surface of the film is bonded to a glass substrate, and the film is then cleaved from the GaAs substrate, leaving the surface of the latter in condition for repeating the procedure. The same GaAs substrate has been used for successive growth of four GaAs films, each about 4 cm2, ranging in thickness from 5 to 10 μm. The electrical properties of a CLEFT film were found comparable to those of conventional VPE layers. The CLEFT process should also be applicable to other semiconductors.

Low‐dislocation‐density GaAs epilayers grown on Ge‐coated Si substrates by means of lateral epitaxial overgrowth

Single‐crystal GaAs layers have been obtained by means of lateral epitaxial overgrowth seeded within stripe openings in a SiO2 mask over GaAs layers grown on Ge‐coated Si substrates. Transmission electron microscope and scanning cathodoluminescence studies indicate that the laterally overgrown GaAs layers have a dislocation density of less than 104 cm−2, compared to 107–108 cm−2 for the GaAs layers grown directly on the Ge/Si substrates. Initial experiments indicate that the electrical properties of the laterally overgrown layers are comparable to those of conventional GaAs epilayers grown on single‐crystal GaAs substrates.

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than 5 have been obtained. The lateral growth is due to surface‐kinetic control for the two‐dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 μm thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

Low‐loss GaAs optical waveguides formed by lateral epitaxial growth over oxide

We report the successful demonstration of a new type of single‐mode semiconductor waveguide, an oxide‐confined optical waveguide, that has lower loss and should have a smaller allowable bend radius than previously reported structures. The waveguides are formed by a new technique of lateral epitaxial growth of single‐crystal GaAs over an SiO2 film. Rib waveguides formed on these epitaxial layers have SiO2 as the lower confining layer and thus have better confinement than comparable all‐semiconductor structures. Losses of only 2.3 dB/cm (0.54 cm−1) have been measured at 1.06 mm.

Lightweight tandem GaAs/CuInSe/sub 2/ solar cells

High-efficiency, ultralightweight, mechanically stacked 4-cm/sup 2/ thin-film tandem solar cells are discussed. The tandem stack consists of a single-crystal, thin-film Ga(Al)As cell fabricated by the cleavage of lateral epitaxy for transfer (CLEFT) process and adhesively bonded to the top of a CdZnS/CuInSe/sub 2/ polycrystalline thin-film cell deposited on glass. Maximum tandem efficiency in a four-terminal configuration of 21.6% AM0 have been demonstrated. This represents the highest thin-film cell efficiency reported to date. Individual subcells with efficiencies of 19.5% for CLEFT GaAs and 3.0% for CuInSe/sub 2/ have also been achieved. Cell specific power as high as 600 W/kg has been achieved with a 4-cm/sup 2/ cell weight of 188 mg without coverglass, at an efficiency of 20.8% AM0. >

Video I/O interface for wearable computers

This paper is a report of work in progress toward the development and testing of a computer interface mounted in eyewear, and capable of both input and output functions. The unique feature of this interface is the use of advanced embedded optical techniques to form eyeglass lenses capable of relaying images internally, without significant optical components in front of the users face. These optical techniques make possible the incorporation of both a camera and display within eyeglasses. The interface also includes audio input and output. The paper discusses methods of constructing such an interface, design considerations, and will describe work in progress to realize working models.

Planar GaAs p‐i‐n photodiode with picosecond time response

A high‐speed planar GaAs p‐i‐n photodiode has been fabricated on a semi‐insulating GaAs substrate. The time response and sensitivity have been characterized in the wavelength range typical of GaAlAs diode lasers. An optoelectronic correlation measurement technique was used to determine the time response. The device exhibits an impulse response of 19 ps full width at half‐maximum to 4‐ps near‐infrared dye laser pulses with an external quantum efficiency of 15%. The device is operated at the low bias voltage of −2 V. The planar electrode design and fabrication on a semi‐insulating substrate make the diode suitable for incorporation in monolithic optoelectronic circuits.

Electronic Properties of Grain Boundaries in GaAs: A Study of Oriented Bicrystals Prepared by Epitaxial Lateral Overgrowth

Abstract : The electronic properties of grain boundaries in GaAs have been investigated. The optoelectronic properties of melt-grown polycrystalline GaAs were studied by cathodoluminescence. This analysis showed that grain boundary properties are influenced by both the boundary structure and the composition of the matrix. For a systematic investigation of the relationship between grain boundary structure and electronic behavior, a technique has been developed for the growth of oriented GaAs bicrystal layers by vapor-phase epitaxy using lateral overgrowth. Using this technique, a series of n-type bicrystal layers containing 110/(111) tilt boundaries with selected misorientation angles ranging from 0 to 30 degrees were grown.

Toward eyeglasses-based electronic displays

The development of a head mounted display concealed within eyeglasses has been a long term objective of many head mounted display (HMD) development efforts. This paper will review design concepts from the literature, with a view toward assessing the practical merits of the various approaches. The factors of importance in miniaturizing a HMD will be summarized. Finally, we will briefly summarize some new approaches including the use of alternative display technology that may lead to a display system hidden within eyeglasses frames.

Eyewear-based displays for personal electronics

This paper addresses the development of eyewear based displays for portable, personal electronics. The personal electronic system applications include the wearable personal computer, portable digital video disk player, and the cellular telephone. We describe progress on integrated eyewear systems, as well as on clip-on systems that can attach to ordinary eyewear. We conclude with a short description of a system that will include a camera, display, and audio system.