Conductive distributed Bragg reflector fabricated by oblique angle deposition from a single material

Abstract

Oblique angle deposition allows the fabrication of nano-structured porous thin films of high optical quality. By selecting the incident angle, the porosity - and thereby, the refractive index - of the deposited film can be tuned to a specific desired value. This makes it possible to fabricate multi-layer optical thin film components consisting entirely of a single material which is chosen for its properties other than refractive index, such as optical absorption or conductivity. As an application for this technique we demonstrate a conductive distributed Bragg reflector (DBR) designed for 460 nm. Common material choices in this wavelength range are SiO₂ and TiO₂; however, both materials are insulating. Conductive DBRs are limited to epitaxially grown doped semiconductors, which generally have low index contrast. The DBR reported here is composed entirely of indium tin oxide (ITO), chosen for its conductivity and low absorption. By varying the deposition angle a refractive index contrast of &Delta;<i>n</i> = 0.4 is achieved, which yields a measured reflectivity of 72.7% for a three-period low-porosity-ITO/high-porosity-ITO DBR. The reflectivity is in excellent agreement with theory.