This paper proposes a 3D optical interconnect system with the integration of a pair of 1D parabolically Graded Index (GRIN) lens to collimate light for free space propagation in order to reduce loss. High quality thick fluorine-doped silica film for the 1D GRIN lens is deposited by a HC-PECVD system. Its periodical refocusing character was tested by fluorescence technique. A novel fabrication technique has been developed to overcome the challenges of integrating the lens with facing-down 45° micro-mirror. The integrated 3D-optical interconnect system is tested and results show a 25dB loss improvement over the system without lens.

Investigators: Dr. Dirk Konig – Characterisation/Modeling Strand Leader, GCEP, CoE Dr. Eun-Chel Cho – Processing Strand Leader, GCEP, CoE Dr. Tom Puzzer – Professional Officer, GCEP, CoE (part time) Ms. Yidan Huang – Professional Officer, GCEP, CoE Dr. Shujuan Huang – Postdoctoral Fellow, GCEP, CoE Dr. Dengyuan Song – Postdoctoral Fellow, GCEP, CoE Dr. Thorsten Trupke – Associate Professor, GCEP, CoE (part time) Dr. Chu-Wei Jiang – Postdoctoral Fellow, GCEP, CoE (part time) Dr. Patrick Campbell – Research Associate, GCEP, CoE (part time) Mr. Edwin Pink – Research Associate, GCEP, CoE (part time)

Tandem PV cells - with their increased efficiency due to a multi-band gap approach - usually involve expensive materials and fabrication. Thin film approaches, with an engineered variation in band gap through the use of quantum confinement in Si quantum dots, offer a cheaper alternative. Presented are characterisation and modelling data on fabrication of such Si and Sri QD nanostructures in various dielectric matrices by self-organised thin film deposition, with demonstrated confined energy levels of 1.7 eV for 2 nm diameter QDs. This being the optimum energy for an upper tandem cell element. (c) 2008 Elsevier B.V All rights reserved.

Superlattices of silicon nanocrystals or quantum dots (QDs) are fabricated by depositing alternating layers of stoichiometric and sub-stoichiometric silicon nitride by dual-mode PECVD and subsequent high temperature annealing. NH3, SiH4 and Ar are used as processing gases. The formation of QDs is monitored for varying annealing temperatures using TEM and GI-XRD. Samples composed of 50 bi-layers are grown under the same conditions and annealed for two hours at temperatures ranging between 600 and 1150°C. A 50 bi-layer superlattice structure of silicon nanocrystals with an estimated average grain size of approximately 4 nm was achieved at 1000°C. The use of FTIR spectroscopy as a complementary technique for verifying the formation of silicon nanocrystals in a nitride matrix is investigated. The IR absorbance spectra for samples containing silicon nanocrystals show a distinct shoulder at 1080 cm-1 corresponding to the Si-O-Si stretching mode possibly due to oxidation. Preliminary evidence is also presented showing the possible formation of α-Si3N4 nanocrystals at 1100 and 1150°C.

High-resolution scanning electron microscope, focused ion beam (FIB) microscope, and electron-beam induced current (EBIC) images are taken on large-grained polycrystalline silicon thin-film diodes on glass. To aid understanding of the plan-view EBIC images obtained, trenches are cut into the diodes in the FIB microscope, and the p-n junction then located and examined in the diode's cross section using high-resolution EBIC. Diffusion of aluminium atoms from the heavily doped emitter region into the base region of the diode along grain boundaries during material fabrication is found to have locally altered the junction's location and therefore alters the EBIC signal in these regions. Using this method allows a fast and easy location of the p-n junction in these diodes, in addition to aiding in the identification of unusual junction deviations which complicate the interpretation of plan-view EBIC images.

A new silicon parallel multilayer solar cell structure has recently been reported which can give high solar cell energy conversion efficiency from low quality silicon material. Advantages of this structure are described as is recent characterization work which compares the properties of grain boundaries in experimental devices to those predicted by earlier calculations.