Measurement of optical constants of TiN and TiN/Ti/TiN multilayer films for microwave kinetic inductance photon-number-resolving detectors

TL;DR

This study measures the optical constants of TiN and multilayer TiN/Ti films to optimize their use in photon detectors, proposing a structure that could achieve near-perfect photon absorption at 1550 nm.

Contribution

It provides the first detailed measurement of optical constants for TiN and multilayer films, enabling improved optical stack design for photon detectors.

Findings

Refractive indices of TiN and multilayer films were successfully measured.

A proposed optical stack can theoretically achieve 100% photon absorption at 1550 nm.

The design enhances the optical efficiency of TiN-based photon detectors.

Abstract

We deposit thin titanium-nitride (TiN) and TiN/Ti/TiN multilayer films on sapphire substrates and measure the reflectance and transmittance in the wavelength range from 400 nm to 2000 nm using a spectrophotometer. The optical constants (complex refractive indices), including the refractive index n and the extinction coefficient k, have been derived. With the extracted refractive indices, we propose an optical stack structure using low-loss amorphous Si (a-Si) anti-reflective coating and a backside aluminum (Al) reflecting mirror, which can in theory achieve 100% photon absorption at 1550 nm. The proposed optical design shows great promise in enhancing the optical efficiency of TiN-based microwave kinetic inductance photon-number-resolving detectors.