Crystallinity Evolution of MOCVD-Grown $\beta$-Ga$_2$O$_3$ Films Probed by In Situ HT-XRD under Different Reactor Heights

TL;DR

This study investigates how reactor height affects the crystallinity and surface quality of MOCVD-grown $eta$-Ga$_2$O$_3$ films using in situ HT-XRD, revealing differences in strain, mosaic alignment, and surface roughness.

Contribution

It provides new insights into the influence of reactor geometry on the structural evolution and surface morphology of $eta$-Ga$_2$O$_3$ films during MOCVD growth.

Findings

Short-chamber films have smoother surfaces than long-chamber films.

Reactor height affects the mosaic alignment and initial crystallinity.

Both film types show similar thermally driven strain responses.

Abstract

The crystallinity of $\beta$-Ga$_2$O$_3$ thin films grown by metal-organic chemical vapor deposition (MOCVD) is strongly influenced by reactor design and the resulting growth environment. In this work, we investigate the role of reactor height on the crystallinity evolution of MOCVD-grown $\beta$-Ga$_2$O$_3$ films by directly comparing long- and short-chamber showerhead configurations. Structural evolution was probed by in situ high-temperature X-ray diffraction (HT-XRD) as the MOCVD-grown films were heated from 25~$^\circ$C to 1100~$^\circ$C. Temperature-dependent XRD reveals a consistent redshift of the $\beta$-Ga$_2$O$_3$~($-201$) reflection after HT-XRD heating and subsequent cooling to room temperature for both reactor geometries, indicating a similar thermally driven strain response. Quantitative rocking-curve analysis shows a non-monotonic temperature dependence of the ($-201$) full width at half maximum (FWHM), with minimum values of approximately 2.03$^\circ$ and 2.72$^\circ$ for the short- and long-chamber films, respectively, reflecting differences in mosaic alignment established during growth. Atomic force microscopy further shows that short-chamber-grown films exhibit smoother surfaces, with root-mean-square roughness values of approximately 7.7~nm before and 7.3~nm after HT-XRD heating, compared to 19.3~nm and 12.3~nm, respectively, for long-chamber-grown films. Overall, these results indicate that reactor height influences the initial crystalline and morphological templates of $\beta$-Ga$_2$O$_3$ films and modulates their elevated-temperature structural response, providing practical insights for optimizing MOCVD reactor design for high-quality $\beta$-Ga$_2$O$_3$ growth.