Microstructural and preliminary optical and microwave characterization of erbium doped CaMoO$_4$ thin films

TL;DR

This study investigates erbium-doped CaMoO$_4$ thin films grown on different substrates, characterizing their microstructure, optical, and microwave properties to evaluate their potential as quantum emitters for quantum networks.

Contribution

It demonstrates controlled growth of high-quality epitaxial CaMoO$_4$:Er films and provides initial optical and microwave characterization relevant for quantum applications.

Findings

Epitaxial growth on YSZ yields high-quality single crystalline films.

Optical linewidth of 9.1 GHz and excited state lifetime of 6.7 ms measured.

Microwave EPR linewidth of 1.10 GHz observed.

Abstract

This work explores erbium-doped calcium molybdate (CaMoO$_4$) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 $\mu$m Er$^{3+}$ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO$_4$ formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO$_4$ films. We perform preliminary optical and microwave characterization on the suspected $Y_1 - Z_1$ transition of 2 ppm, 200 nm epitaxial CaMoO$_4$ annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.