  Atomic short-range order (SRO) in direct-bandgap GeSn for infrared photonics
has recently attracted attention due to its notable impact on band structures.
However, the SRO in GeSn thin films grown by different methods have hardly been
compared. This paper compares SRO in GeSn thin films of similar compositions
grown by molecular beam epitaxy (MBE) and chemical vapor deposition (CVD) using
atom probe tomography. An $\sim$15% stronger preference for Sn-Sn 1$^{st}$
nearest neighbor (1NN) is observed in MBE GeSn than CVD GeSn for both thin film
and quantum well samples with Sn composition ranging from 7 to 20%.
Interestingly, samples grown by different deposition tools under the same
method (either MBE or CVD) showed remarkable consistency in Sn-Sn 1NN SRO,
while MBE vs. CVD showed clear differences. Supported by theoretical modeling,
we consider that this difference in SRO originates from the impact of surface
termination, where MBE surfaces are exposed to ultrahigh vacuum while CVD
surfaces are terminated by H to a good extent. This finding not only suggests
engineering surface termination or surfactants during the growth as a potential
approach to control SRO in GeSn, but also provides insight into the underlying
reasons for very different growth temperature between MBE and CVD that directly
impact the strain relaxation behavior.
