http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Jo, Hyun-Jun,Kim, Jong Su,Ryu, Mee-Yi,Yeo, Yung Kee,Kouvetakis, John Elsevier 2018 THIN SOLID FILMS - Vol.645 No.-
<P><B>Abstract</B></P> <P>Temperature-dependent photoreflectance (PR) measurements for Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB>/Ge/Si films treated with a hydrogen inductively coupled plasma (H<SUB>2</SUB>-ICP) have been performed. The Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB> film is grown on Ge-buffered Si substrate by ultra-high vacuum chemical vapor deposition method, and the H<SUB>2</SUB>-ICP treatment was carried out for 5min for the Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB> epitaxial layer. The high-resolution X-ray diffraction results show that the compressive strain of the Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB> layer decreases and the tensile strain of the Ge buffer layer increases after H<SUB>2</SUB>-ICP treatment. The PR spectrum of as-grown Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB>/Ge/Si film at 300K consists of three signals at 0.603, 0.782 and 0.814eV, which are assigned to the direct transitions from conduction Γ valley to the valence bands related to the surface of Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB>, the Ge/Si and GeSn/Ge interfaces, respectively. After H<SUB>2</SUB>-ICP treatment, two PR signals of 0.604 and 0.781eV were obtained at 300K and they are attributed to the direct transition energies of the Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB> and the Ge buffer layer, respectively. As temperature decreases, new weak PR signals appear in the lower energy regions of both PR signals from the H<SUB>2</SUB>-ICP treated GeSn and Ge layers at 210K and 130K, respectively, due to the increase of tensile strain in Ge layer while no new signal appears for the as-grown sample. The PR spectrum of the H<SUB>2</SUB>-ICP treated sample at 10K shows four signals, and these signals are assigned to the surface of GeSn and GeSn at the interface between GeSn and Ge buffer layers, the Ge at the interface between GeSn and Ge buffer layers, and the Ge at the interface between Ge buffer layer and Si substrate, respectively. These PR results indicate that H<SUB>2</SUB>-ICP treatment significantly affects the strain and defects near the interface between GeSn and Ge layers, and thus optical properties of GeSn layer are also altered by H<SUB>2</SUB>-ICP treatment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photoreflectance spectroscopy of a Ge<SUB>0.938</SUB>Sn<SUB>0.062</SUB>/Ge/Si films from 12 to 300K </LI> <LI> In PR spectrum, four direct transitions attributed to GeSn and Ge are observed. </LI> <LI> With decreasing temperature, the tensile strain of Ge buffer layers is changed. </LI> </UL> </P>
Harris, Thomas R.,Ryu, Mee-Yi,Yeo, Yung Kee,Beeler, Richard T.,Kouvetakis, John Elsevier 2014 Current Applied Physics Vol.14 No.1
The electrical properties of p-type Ge, Ge1-ySny, and Si0.09Ge0.882Sn0.028 samples grown on n-type Si substrates using ultra-high vacuum chemical vapor deposition have been investigated as a function of temperature. Degenerate parallel conducting layers were found in all Ge/Si, Ge1-ySny/Si, and Si0.09Ge0.882Sn0.028/Si samples, which are believed to be associated with dislocation defects at the interface produced by the lattice mismatch between the two materials. These degenerate conducting layers affect the electrical properties of all the thin epitaxial films. Additionally, temperature dependent Hall-effect measurements show that these materials exhibit a conductivity type change from p to n at around 370-435 K. The mobilities of these samples are generally lower than that of bulk Ge due to carrier scattering near the interface between the epitaxial layer and the Si substrate and also due to alloy scattering. Detailed behavior of temperature-dependent conductivity of these samples is also discussed. (C) 2013 Elsevier B.V. All rights reserved.
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.
조현준,Geun-Hyeong Kim,김종수,류미이,Yung Kee Yeo,Thomas R. Harris,John Kouvetakis 한국물리학회 2016 Current Applied Physics Vol.16 No.1
Temperature- (T-) dependent photoreflectance (PR) measurements have been made for the tensilestrained, undoped Ge0.985Sn0.015 film grown on n-Si substrate by ultra-high vacuum chemical vapor deposition method. The PR spectra at room temperature consist of two signals at around 0.739 and 1.022 eV, which are assigned to the direct transitions from conduction G valley to valence and spin-orbit split-off bands, respectively. The T-dependent PR measurements show tensile-strain split direct bandgap transitions from the G valley to the light-hole (ELH) and heavy-hole (EHH) bands at energies of 0.772 and 0.803 eV at 12 K, respectively, which are not usually observable from the photoluminescence measurements for relatively high Sn content Ge1-ySny samples. The PR signals for both HH and LH bands are blue shifted and their intensities decrease with increasing temperature, but both LH and HH PR signals persist through 240 K and only one HH PR signal is observed at room temperature. It has been observed that the separation energy between the EHH and ELH increases as T decreases, which clearly indicates an increase in tensile strain as T decreases. From the analysis of the T-dependent separation energy between the ELH and EHH, the T-dependent tensile strain in the Ge0.985Sn0.015 film was obtained, which might not be easily measured using the X-ray diffraction method.
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>