Comparative analysis of electro-optic properties in monocrystalline and polycrystalline AlN

The crystallinity of a material often plays a significant role in determining its material properties. Aluminum nitride (AlN), which has emerged as a promising material for photonics in the past few decades, can be polycrystalline or monocrystalline in nature. Previously, the electro-optic (EO) coefficient of polycrystalline and bulk monocrystalline AlN has been reported. However, to the best of our knowledge, the EO coefficient of thin-film monocrystalline AlN has not yet been reported. In this work, we report the EO coefficient of thin-film monocrystalline AlN and make a side-by-side comparison with the EO coefficient of polycrystalline AlN. We used the resonant shift of a microring resonator to measure the EO coefficients for both transverse electric (TE) and transverse magnetic (TM) modes in the telecom C-band. For monocrystalline AlN, we observe surface effects that cause bias drift, which can be eliminated through annealing. The EO coefficients we measured for monocrystalline and polycrystalline AlN are comparable, with the EO of annealed monocrystalline AlN being slightly higher.