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RISS 인기검색어
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- 저자 : Hogsed, M.R. (검색결과 2 건)
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Wang, Buguo,Harris, T.R.,Hogsed, M.R.,Yeo, Y.K.,Ryu, Mee-Yi,Kouvetakis, J. Elsevier 2019 THIN SOLID FILMS - Vol.673 No.-
<P><B>Abstract</B></P> <P>Temperature-dependent photoluminescence (PL) of two sets of ternary samples with fixed tin concentrations of ~5.2% (Ge<SUB>0.924</SUB>Si<SUB>0.024</SUB>Sn<SUB>0.052</SUB>, and Ge<SUB>0.911</SUB>Si<SUB>0.036</SUB>Sn<SUB>0.053</SUB>) and ~7.3% (Ge<SUB>0.90</SUB> <SUB>0</SUB>Si<SUB>0.027</SUB>Sn<SUB>0.073</SUB>, and Ge<SUB>0.888</SUB>Si<SUB>0.04</SUB>Sn<SUB>0.072</SUB>) were measured along with their binary counterparts (Ge<SUB>0.948</SUB>Sn<SUB>0.052</SUB> and Ge<SUB>0.925</SUB>Sn<SUB>0.075</SUB>). The variations of direct bandgap emission (E<SUB>D</SUB>) and indirect bandgap emission (E<SUB>ID</SUB>) with temperature were studied for both ternary and binary alloys by means of Gaussian curve fitting, and the results are compared. The bandgap widths of ternaries clearly increase after Si incorporation into the GeSn with similar Sn concentrations. It is found that for the ternaries both E<SUB>D</SUB> and E<SUB>ID</SUB> peak energies are blue shifted, and the energy separation of E<SUB>D</SUB> and E<SUB>ID</SUB> peaks becomes larger than that of binaries for similar Sn concentrations. Moreover, both E<SUB>D</SUB> and E<SUB>ID</SUB> peaks appear at room temperature (RT) in the GeSiSn spectra, but the E<SUB>D</SUB> peak position is greater than E<SUB>ID</SUB>, indicating these ternaries are indirect bandgap materials. Low temperature PL validates the existence of indirect PL emission in Ge<SUB>0.90</SUB>Si<SUB>0.027</SUB>Sn<SUB>0.073</SUB> and direct gap behavior in Ge<SUB>0.925</SUB>Sn<SUB>0.075</SUB>, indicating GeSn becomes a direct bandgap material at lower Sn concentration than GeSiSn. The PL intensities of these ternaries are generally weaker and the spectra become more complicated than those of binaries, probably due to increased strain and defects in the ternaries. Finally, it is found that the effect of large differences in strain of ternary samples on PL peak positions can be greater than that of small Si composition differences in ternaries. A large compressive strain in ternaries can also make splitting of the E<SUB>D</SUB> into E<SUB>D,HH</SUB> (conduction band minimum-Γ valley to heavy hole maximum) and E<SUB>D,LH</SUB> (conduction band minimum-Γ valley to light hole maximum) transitions more observable in the PL spectra.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Temperature-dependent photoluminescence of GeSn and GeSiSn (~5.2 and 7.3% Sn) are analyzed. </LI> <LI> Variations of the direct and indirect bandgap emissions of GeSn and GeSiSn are compared. </LI> <LI> GeSn becomes a direct bandgap material at lower Sn concentration than GeSiSn. </LI> <LI> Strain effects on PL peak energy larger than small Si content variations in GeSiSn. </LI> <LI> Large compressive strain makes light/heavy hole splitting of E<SUB>D</SUB> apparent in GeSiSn. </LI> </UL> </P>
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류미이,Thomas R. Harris,Buguo Wang,Yung Kee Yeo,Michael R. Hogsed,이상조,김종수,John Kouvetakis 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.8
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.
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