Mathieu Halbwax

Impact of the firing step on Al2O3 passivation on p-type Czochralski Si wafers: Electrical and chemical approaches

The development of an efficient surface passivation is a key feature of silicon solar cells towards the improvement of €/W ratio. An Al2O3 layer coated by plasma-enhanced atomic layer deposition has proven its efficiency to increase the minority carrier lifetime on p-type silicon. However, the firing step, which is a common part of the manufacturing process that includes metallic pastes for screen-printed contacts, ruins this passivation effect. On the basis of photoelectric, electric, and chemical experimental studies, a correlation is provided in this paper between the different microscopic and macroscopic behaviors that govern the passivation process. To show this correlation, photoconductance decay measurements have been carried out to determine minority carrier lifetime. Following which, the capacitance–voltage measurement results are used to extract electrical parameters, namely, the densities of interface defects and effective charges. In addition, complementing secondary ion mass spectrometry (SIMS) experiments revealed the different chemical species that can be relevant for the explanation of passivation quality and macroscopic electrical measurements.

40 GSPS all-optical ADC with ENOB of 6.6 using EO polymer optical deflector and spatial quantizer

40GSPS analog-to-digital converters (ADC) are required for realization of digital receivers up to 20GHz. An all optical ADC is presented using an optical deflector for spatial sampling. The optimized design of optical deflector is based on optical beam propagation and finite element modeling electromagnetic modeling. An effective number of bits (ENOB) of 6.6 ADC is achieved under a ±20V RF voltage swing and by minimalizing angular resolution with a leaky waveguide of 2cm long. Design and implementation of a polymer waveguide are presented, meeting the leaky waveguide coefficient of 0.1Np/cm and low optical attenuation with quality optical waveguide surface flatness better than 20nm. A broadband (2-40GHz) transition from coplanar waveguide (CPW) to coupled microstrip (CMS) transmission lines is presented that overcomes the RF attenuation to achieve under 0.06Np/cm variation by using a pre-emphasis filter with a flat group delay of less than 70ps.