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Microstructure and Photoluminescence Properties of GeSn/Ge MQWs
and GeSn Film on Ge (001)
T. Liu, L. M. Wang, X. F. Hu, Z. Y. Zhong, X. J. Yang, Z. M. Jiang*
State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
Introduction
 Type-I band energy structure may be
obtained in GeSn/Ge MQWs, which
can enhance the light efficiency in
group-IV semiconductors.
 Si-based optical interconnection technology is
considered to be most promising technology
due to advanced Si IC technology.
 In recent years, lots of efforts have been made in
the epitaxial growth of high-quality GeSn crystals
to achieve direct bandgap light emitting.
 S. Wirths et al., Nature Photonics, 9 (2), 88-92 (2015).
 R. Chen et al., Nano Letters, 14 (1), 37-43 (2014).
Microstructure and photoluminescence properties of GeSn/Ge MQWs and GeSn film
Raman spectra of GeSn/Ge MQWs
(black line), GeSn film (red line)
and Ge substrate (blue line).
Structure schematic of samples: (a) GeSn/Ge MQWs and (b) GeSn film on
Ge(001) substrates.
 Compared to Ge substrate, the Ge-Sn and the Sn-Sn peaks from the GeSn layers were observed
in both samples.
 Two Raman spectra look quite identical, so Raman spectra could not distinguish the difference
in microstructure between both samples.
Cross-sectional HRTEM images of (a) GeSn/Ge MQWs and (b) GeSn film.
 Based on the contrasts in GeSn layers, it can be found that Sn atoms in MQWs
distributed uniformly than in the thicker film.
PL spectra of GeSn/Ge MQWs
(black line) and GeSn film (red line)
at 20 K.
 Two spectra are very close, and the PL peaks are found to be at the same energy of 0.62 eV.
 It is noteworthy that although the total thickness of GeSn layers in the MQWs sample (40nm)
is much smaller than that of the film sample (200 nm), the PL intensities of the two samples
are almost the same.
Conclusions
Two-dimensional x-ray diffraction reciprocal space mappings of (a) GeSn/Ge
multi-quantum wells and (b) GeSn film around Ge (224) Bragg reflection.
 It is clearly seen that the GeSn layers are fully strained.
 The Sn concentrations are calculated to be 2.2 % and 2.7 %, respectively.
 Ge1-xSnx/Ge MQWs and Ge1-xSnx film samples were grown on Ge (001).
 The Sn concentration and the strain in the GeSn layers were characterized by XRD mappings.
 Although the total thickness of GeSn layers in the MQWs (40nm) is much smaller than that
of the film sample (200 nm), the PL intensities of the two samples are very close.
 It means that the optical properties of the GeSn/Ge MQWs are better than that of the GeSn
film, which is explained in terms of crystal quality and quantum confinement effect.