Indirect Wafer Bonding and Epitaxial Transfer of GaSb-Based Materials

Results from a study of indirect wafer bonding and epitaxial transfer of GaSb-based materials are presented. Benzocyclobutene (BCB) was used as a bonding agent to bond GaSb and epitaxial structures lattice matched to GaSb onto Si, GaAs, and sapphire carrier substrates. To better understand sources of stress during the bonding process, which can result in cracking and subsurface damage of the GaSb-based materials, BCB’s hardness and reduced elastic modulus were measured at various stages during the curing process. Based on the results of curing experiments, a bonding and epitaxial transfer process for GaSb-based materials was then developed. Following bonding, using an experimentally determined low-stress cure cycle, GaSb substrates were removed from epitaxial layers of InAsSb using a combination of mechanical thinning and polishing followed by selective chemical etching using a hydrofluoric and chromic acid solution. Etch selectivity data are also presented where selectivity greater than 100:1 is achieved for GaSb:InAsSb

High-optical-quality nanosphere lithographically formed InGaAs quantum dots using molecular beam epitaxy assisted GaAs mass transport and overgrowth

Optically active, highly uniform, cylindrical InGaAs quantum dot ͑QD͒ arrays have been fabricated using nanosphere lithography combined with Bromine ion-beam-assisted etching and molecular beam epitaxy ͑MBE͒-assisted GaAs mass transport. Previously fabricated QD nanopillar arrays showed significant degradation of optical properties due to the etch damage. Here, a novel mass transport process in a Riber 3200 was performed to encapsulate the lithographically defined InGaAs disk QDs in a GaAs matrix, resulting in the passivation of the etch-damaged QD sidewall layer. Photoluminescence emission intensity following the mass transport process increased by a magnitude of 4-10 as compared to that from unprocessed nanopillar sample. In addition, a PL peak energy redshift was observed after mass transport, presumably due to the decrease in the lateral barrier potential from vacuum to GaAs, as well as the elimination of the depletion layer. Furthermore, the mass transport process in the high vacuum MBE environment enables GaAs overgrowth with few defects and dislocations following mass transport for surface planarization. PL emission intensity increased by an additional factor of 4 following GaAs overgrowth, bringing the QD intensity to 1 2 of that of the original single quantum well. Thus, the potential of the MBE-assisted mass transport process has been demonstrated to fabricate high optical quality InGaAs quantum dots encapsulated in a GaAs matrix for device applications

Compound Semiconductor Materials and Devices

Contains table of contents for Part I, table of contents for Section 1, reports on fourteen research projects and a list of publications.Defense Advanced Research Projects Agency/National Center for Integrated Photonics TechnologyFannie and John Hertz Foundation Graduate FellowshipJoint Services Electronics Program Grant DAAH04-95-1-0038National Science Foundation Graduate FellowshipNTT CorporationNational Science FoundationU.S. Navy - Office of Naval ResearchToshiba CorporationAT&T Bell Laboratories Graduate Fellowshi

Compound Semiconductor Materials and Devices

Contains table of contents for Part I, table of contents for Section 1, an introduction, reports on fourteen research projects and a list of publications.Defense Advanced Research Projects Agency/National Center for Integrated Photonics TechnologyJoint Services Electronics Program Grant DAAH04-95-1-0038MIT Lincoln LaboratoryNational Science Foundation Graduate FellowshipU.S. Navy - Office of Naval ResearchAT&T Bell Laboratories FellowshipU.S. Army - Ft. MeadeNTT CorporationNational Science FoundationLockheed-Martin Corporatio

Changes in spore chemistry and appearance with increasing maturity

Sporopollenin is the primary biopolymer found in the walls of pollen and spores; during maturation sporopollenin undergoes a number of discrete chemical changes, despite maintaining identifiable morphological features which can be exploited for palynological study. Here we report the results of heating experiments performed using Lycopodium clavatum spores designed to investigate the changes that occur within sporopollenin across a wide range of temperatures (0–350 °C) to simulate different degrees of maturation. Changes in sporopollenin functionality were assessed using Fourier transform infrared (FTIR) microspectroscopy. Our analyses show that the chemical structure of sporopollenin remains relatively stable over a wide range of simulated maturation conditions, until a threshold of 250–300 °C is reached, at which point a reorganisation of chemical structure begins. Comparison of these artificially matured sporeswith fossil material obtained froma Carboniferous-age section in the United Kingdom shows a strong chemical resemblance, suggesting that our experimental procedure accurately reflects the process of maturation and provides an insight into the chemical stability of sporopollenin in the geosphere