Rotatable Offner imaging system for ellipsometric measurement

To realize high spatial resolution imaging ellipsometric measurement with large field of view, we developed a rotatable Offner system with unit magnification. When the conventional Offner imaging system is tilted relative to the sample plane for the ellipsometric measurement, only a small region of plane is in focus. The rotatable Offner system developed here renders the entire object in focus through all rotations. The performance of the prototype of the Offner system and imaging ellipsometer is tested by generating maps of the ellipsometric parameters Δ and Ψ for samples such as a silicon wafer and a resolution target made of chromium film evaporated on a glass substrate.

Enhancing the External Quantum Efficiency of Porous Silicon LEDs Beyond 1 % by a Post-Anodization Electrochemical Oxidation

External quantum efficiencies (EQEs) of electroluminescent devices based on porous silicon (PS) reported to date are still below the minimum requirements for practical applications such as display devices (1 %) and optical interconnection (10 %). Post-anodization anodic oxidation of PS to enhance the EQE of electroluminescence from devices based on a thin transparent indium tin oxide contact mounted on either porosified n+-type silicon or p+n+-type silicon has been investigated. Enhancement of EQE by more than 2 orders of magnitude has been achieved on our devices. CW EQE of 0.51% has been obtained by using a single anodically oxidized n+-type porous layer. The device based on the p+n+ substrate yielded a CW EQE of 1.1 %, with a power efficiency of 0.08%. It is the first time that EQE greater than 1% is obtained. Furthermore, anodically oxidized devices show better stability than non-oxidized devices. The anodic oxidation proceeds in such a way that it mainly decreases the size of nonconfined silicon in PS. The dramatic enhancement in EQE can therefore be explained by preferential reduction of leakage carrier flow through non-confined silicon.