Mark Gross

Mechanisms of photosensitivity in germanosilica films

Mechanisms underlying the refractive index changes in germanosilica films deposited by hollow cathode plasma enhanced chemical vapor deposition and subjected to UV irradiation are proposed based on observed changes in film thickness, stress, and structure. An increase in refractive index after UV exposure is observed in films deposited under low ion bombardment conditions. This increase in refractive index is accompanied by a reduction in film thickness which is an order of magnitude larger than that expected from the Lorentz–Lorentz relation. This behavior is shown to result from: (i) a significant degree of porosity in the as-deposited material; (ii) oxygen deficiency of the as-deposited material. Upon UV irradiation, the porous structure is compacted, thus accounting for the large decrease in thickness, while the oxygen deficiency is reduced causing a decrease in the material polarizability and counteracting the effect of the thickness reduction. On the other hand, germanosilica deposited under high io...

Effect of reactive ion etching–generated sidewall roughness on propagation loss of buried‐channel silica waveguides

Different mask materials (photoresist and amorphous silicon) and different sample temperatures can influence the roughness of sidewalls produced during reactive ion etching of silica. Buried‐channel waveguides with different microroughness on the core sidewalls (corrugation periods less than 1 μm) have been fabricated and characterized for their propagation loss at 1.3 μm wavelength. An increase in the sidewall roughness amplitude of around 0.05 μm results in an increase in the propagation loss of 0.2 dB/cm. Sidewall roughness with a larger period appears to have smaller effect on loss.

16.4% efficient, thin active layer silicon solar cell grown by liquid phase epitaxy

An energy conversion efficiency of 16.4% is reported for a silicon solar cell of 4.11 cm2 total area with a thin active layer of 32 μm grown by liquid phase epitaxy (LPE). This is the highest ever total area efficiency for a cell of this type and is due to a number of improvements over earlier reported results. The thin active layer was grown by LPE on an inactive silicon substrate from an indium solution in a 20% hydrogen/argon forming gas mixture ambient rather than pure hydrogen. Higher current density and efficiency than previously reported for similar cell structures have been achieved by employing microgroove texturing of the front surface, a very shallow (0.25 μm) and high sheet resistivity (220 Ω□) top surface phosphorus diffusion, an optimized ZnS/MgF2 double layer antireflection coating on top of a 200A thick, high quality passivation SiO2 layer, a large aspect ratio (0.45) for the metal contacts, and a graded doping level within the 32 μm thick LPE active layer. The effect of the improved techniques on the cell performance and the properties of the thin active layers are discussed.

Fabrication of light-turning mirrors in buried-channel silica waveguides for monolithic and hybrid integration

A technique for incorporating a mirror into the core of a silica-based channel waveguide is described. Both up reflecting mirrors for hybrid integration and down-reflecting mirrors for monolithic integration can be fabricated using this technique. The proposed fabrication method is based on a combination of low temperature hollow cathode PECVD for silica-based waveguide deposition and a novel technique for forming a reflecting facet by wet chemical etching of PECVD silica.

Fabrication of low-temperature PECVD channel waveguides with significantly improved loss in the 1.50-1.55-μm wavelength range

By excluding nitrogen-containing gases from the deposition process, silica-based waveguides have been fabricated by PECVD at low temperature with a propagation loss less than 0.2 dB/cm in the 1.50-1.55-/spl mu/m wavelength range. PECVD is performed in a high-plasma-density hollow cathode system from a mixture of oxygen and silane. Carbon tetrafluoride is used as a fluorine dopant to depress the refractive index in the buffer and cladding layers. A controllable refractive index change in the range 0.004-0.02 can be obtained.<<ETX>>

The use of silicon nitride in buried contact solar cells

Silicon nitride offers many potential benefits to the family of buried contact fabrication sequences including improved design flexibility and efficiency. The main device structures of the buried contact family comprise the standard buried contact, the simplified buried contact and the double-sided buried contact cells. The physical properties of silicon nitride allow it to be used for surface passivation, as an anti-reflection coating, as a diffusion source material and as a masking dielectric. The use of silicon nitride in each buried contact fabrication sequence is described in this work.

Measurement of ion induced damage‐profiles in GaAs

In this study, with the use of a sensitive optical technique, we demonstrate the possibility of measuring the depth distribution of damage in GaAs that is generated by various ion‐assisted processes such as ion implantation and ion assisted plasma etching. We have used this technique to measure the depth distribution of damage in both He and Ar implanted GaAs and in inert gas and reactive ion etched GaAs. The sensitivity of the technique allowed us to measure damage profiles over a large range of ion energies and ion doses. We have also confirmed previously published results indicating that damage created by sputter etching is inversely proportional to the mass of the ions used in the etching process.

Very low light-reflection from the surface of incidence of a silicon solar cell

This paper reports very low light-reflection from the surface of incidence of a silicon solar cell. The measured hemispherical front surface light-reflectance of our epi thin film silicon solar cell is 1% over the optimum wavelength range 560 to 860 nm and below 2% in the range 440 to 960 nm. These reflectances are the lowest ever achieved for any silicon solar cell. The low reflection has resulted in a 7.9 mA/cm2 higher current density and a 4.5% higher efficiency than those of our best thin film silicon solar cell prior to the optimisation described.

Novel cantilever-beam field-emission pressure sensor

Due to an increasing interest in the study of field emission emitters for vacuum microelectronic devices a variety of new designs on cold cathodes were reported. In this paper we will report a novel pressure sensor utilizing the field-emission from two cantilever beams on a thin pressure sensitive silicon diaphragm. A simulation of the normalized output current as a funcfion of applied pressure is presented. Results of experimental cantilever-beam field-emission pressure sensor and some of the emission phenomena are reported.

Differential reflectance spectroscopy of semiconductors

Differential reflectance (DR) spectroscopy, applied to semiconductors, is shown to be equivalent in some cases to a contactless electro-reflectance technique. DR spectra are achieved by modifying one half of the sample surface or, in the case of semiconductor alloys, just relying on the inhomogeneities present. Our DR spectra of GaAs reveal sharp critical point structures and are comparable to the known electro-reflectance data. The DR spectra show a marked improvement in signal to noise ratio over photoreflectance spectra of the same samples. This new technique has also been used to characterize 111-V quantum well structures.