Temperature-Dependent Photoluminescence Studies of Ge1−ySny (y = 4.3%–9.0%) Grown on Ge-Buffered Si: Evidence for a Direct Bandgap Cross-Over Point
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The temperature (T)-dependent photoluminescence (PL) from Ge1−ySny (y = 4.3%–9.0%) alloys grown on Ge-buffered Si substrates was studied as a function of the Sn content. The PL from Ge1−ySny alloys with high Sn contents (≥7.0%) exhibited the typical characteristics of direct bandgap semiconductors, such as an increase in the PL intensity with decreasing T and a single PL peak corresponding to a transition from the direct bandgap (Γ-valley) to the valence band at all temperatures from 10 to 300 K. For the Ge1−ySny alloys with low Sn contents (≤6.2%), the PL emission peaks corresponding to both the direct bandgap (ED) and the indirect bandgap (EID) PL appeared at most temperatures and as T was increased, the integrated PL intensities of ED initially increased, then decreased, and finally increased again. The unstrained ED and EID energies estimated from the PL spectra at 75 and 125 K were plotted as functions of the Sn concentration, and the cross-over point for unstrained Ge1−ySny was found to be about 6.4%–6.7% Sn by using linear fits to the data in the range of Sn contents from 0% to 9.0%. Based on the results at 75 and 125 K, the cross-over Sn concentration of unstrained Ge1−ySny should be about 6.4%–6.7% Sn content at room temperature. The ED energies of the Ge0.925Sn0.075 alloys were estimated from the T-dependent photoreflectance spectra, and the ED values was consistent with those obtained from PL spectra.
KeywordsGermanium tin Alloys Photoluminescence Ultra-high vacuum chemical vapor deposition Photoreflectance
PACS numbers78.55.-m 68.55.ag 81.15.Gh 61.66.Dk
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The authors would like to express their sincere appreciation to Dr. Gernot S. Pomrenke of the Air Force Office of Scientific Research for his support of this work. This research (MYR) was also supported in part by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2017 R1A2B4003744). This research (B.W.) was supported in part by an appointment to the Faculty Research Participation Program at AFIT, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and AFIT. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government.
- J. S. Kim et al., J. Korean Phys. Soc. 39, S246 (2001).Google Scholar