Michael M. Crouse

Self-ordered pore structure of anodized aluminum on silicon and pattern transfer

A practical approach of transferring a hexagonal array of nanosized pores produced in porous alumina into silicon and other substrates is discussed. The alumina pores have dimensions of 25–250 nm pore diameters and 50–300 nm pore spacings depending on the anodization conditions used. The characteristics of the alumina pores and the alumina–silicon interface are studied for different substrate materials and anodizing conditions. The unique structure of the barrier layer allows for the alumina to be directly used as an etch mask for pattern transfer into the silicon substrate.

Nanoporous Alumina Template with In Situ Barrier Oxide Removal, Synthesized from a Multilayer Thin Film Precursor

A nanoporous alumina template made from a multilayer metal film structure has been developed that allows for the in situ removal of the electrically insulating alumina barrier layer, exposing a Pt electrode at the pore bases. This barrier-free nanoporous system is of great use for dc electrodeposition of a wide variety of materials in the alumina pores. This work in particular describes the development of a multilayer thin film precursor consisting of a Si substrate with thin Pt and Ti and a thicker Al layer in that order. After the Al is anodized, producing the porous alumina, the resulting TiO 2 is selectively removed at the base of the alumina pores exposing the Pt electrode. The metals in the precursor perform different roles in the fabrication and allow the alumina template to be fabricated directly on the final substrate with no film transfer technique involved. This allows Si to be used as the substrate, which could then include electronic circuitry. Several techniques are used to analyze the resulting template.

Self-assembled nanostructures using anodized alumina thin films for optoelectronic applications

Anodized aluminum has recently attracted much attention because of its desirable porous structure. The pore structure is a self-ordered hexagonal array of cells with cylindrical pores in an alumina matrix of variable sizes with diameters of 25 to 300 nm with depths exceeding 100 /spl mu/m depending on the anodizing conditions used. These properties make anodized aluminum a desirable material for many optoelectronic devices including polarizers, photonic crystals, low threshold current lasers, and investigation of light-surface plasmon interactions in metals. The conventional approach to fabricate porous alumina is to use bulk or thin sheets of aluminum and then replicate this pattern into the desired substrate by one of several methods involving a tedious film transfer. However, in this work, a more convenient and practical method of fabricating the porous alumina structure using an evaporated film of aluminum on silicon and other substrates, subsequent pattern transfer, and its use in optoelectronic applications will be discussed.

PN junction fabrication of solar cells and integration with metamaterials

Silicon is the primary material used for the fabrication of solar cells and it is responsible for about 40% of the cost. Metamaterials show promise in enhancing the performance of silicon solar cells thus, improving the efficiency. Here we report on the fabrication of a broadband, antireflective, conductive metamaterial capable of channeling light into a solar cell. As a precursor to making the metamaterial, standard p-n junctions were fabricated. Conventional phosphorus oxychloride (POCl3) furnace diffusion was used to create the p-n junction. When the p-n junction was forward biased, the measured current exhibited a diode characteristic. The measured photocurrent response yielded an open circuit voltage for the p-n junction at 0.48 VDC. The metamaterial film was fabricated, placed atop the p-n junction and characterized. Initial tests showed that the metamaterial antireflective properties were on par with those of standard industrial single-layer silicon nitride coatings. Further testing is being performed to assess the full optical and electrical performance of the metamaterial film.

Fabrication, characterization of II-VI semiconductor nanowires and applications in infrared focal plane arrays

The fragile nature of alumina and the intrinsic Al2O3 barrier layer at the pore bases has hindered its use in optoelectronic devices. In this work, these issues have been addressed by the development of a nanoporous alumina template directly on a silicon substrate with platinum electrodes at the pore bases. This template was then used to perform dc galvanostatic electrochemical deposition of II-VI semiconductor heterostructure nanowires that were then used to fabricate pixilated detector arrays.

Design and fabrication of novel II-IV semiconductor quantum wire infrared detectors/sensors

A nanoporous alumina template made from a multilayer metal film structure has been developed that allows for the in situ removal of the electrically insulating alumina barrier layer, exposing a Pt electrode at the pore bases. This barrier free nanoporous system has great potential for DC electrodeposition of a wide variety of materials in the alumina pores. The nanoporous template is fabricated in a more practical way than existing techniques and can be used for the fabrication of nanowires of many materials. Because the template is fabricated directly on the final substrate, no film transfer technique is needed and the substrate can include electrical circuitry. A silicon substrate may be used that provides mechanical stability, facilitates processing, and allows integration with IC components. This will allow for cheap and high efficiency infrared detectors to be fabricated in a practical and cost effective way. The quantum wire devices fabricated in this way can be customized to be used as infrared sensors at a variety of infrared wavelengths.