UV anti-reflection coatings for use in silicon detector design

TL;DR

This paper presents a novel multi-layer anti-reflection coating approach for silicon CCD detectors to achieve high quantum efficiency across the UV spectrum, addressing the limitations of single-layer coatings.

Contribution

It introduces a multi-layer coating strategy optimized for UV wavelengths, improving quantum efficiency in silicon detectors over a broad UV range.

Findings

Achieved theoretical QE > 60% from 120-300nm

Tested various materials and deposition techniques for optimal coatings

Demonstrated coatings on live devices with minimized reflectance

Abstract

We report on the development of coatings for a CCD detector optimized for use in a fixed dispersion UV spectrograph. Due to the rapidly changing index of refraction of Si, single layer broadband anti-reflection coatings are not suitable to increase quantum efficiency at all wavelengths of interest. Instead, we describe a creative solution that provides excellent performance over UV wavelengths. We describe progress in the development of a CCD detector with theoretical quantum efficiencies (QE) of greater than 60% at wavelengths from 120 to 300nm. This high efficiency may be reached by coating a backside illuminated, thinned, delta-doped CCD with a series of thin film anti-reflection coatings. The materials tested include MgF2 (optimized for highest performance from 120-150nm), SiO2 (150-180nm), Al2O3(180-240nm), MgO (200-250nm), and HfO2 (240-300nm). A variety of deposition techniques were tested and a selection of coatings which minimized reflectance on a Si test wafer were applied to live devices. We also discuss future uses and improvements, including graded and multi-layer coatings.