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The Synthesis And Band Alignment Of ?-? Semiconductor Heterostructures

Posted on:2020-06-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:T Y ShuFull Text:PDF
GTID:1368330575499124Subject:Radio Physics
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In the history of scientific development,physicists have discovered many novel and important physical phenomena at the semiconductor heterojunction interface.?-? narrow-band gap telluride semiconductors(PbTe,PbSe and SnTe,ect.)with the advantages of high photoelectric conversion efficiency,narrow direct band gap,low thermal conductivity and large Seebeck coefficient,have important applications in mid-infrared optoelectronics and thermoelectric devices and have received much attention from research teams worldwide.The work of this paper is mainly to study the synthesis of ?-? semiconductors and the basic properties of their heterojunctions.The innovations achieved are as follows:(1)CdTe/ZnTe buffer layer,a semiconductor heterojunction material,was used to epitaxially grow a PbTe film on a GaAs(211)substrate using molecular beam epitaxy(MBE).The crystal structure,optical and electrical properties of the epitaxial PbTe indicate that the growth of PbTe on the substrate has a narrow growth window around 250?.In situ RHEED observed a shift in growth mode from 2D to 3D,which is consistent with the results of atomic force microscopy(AFM)and scanning electron microscopy(SEM).High-resolution X-ray diffraction(HRXRD)shows that the growth of the PbTe crystal changes from the[211]substrate orientation of GaAs to the[531]direction.A plurality of phonon modes associated with PbTe were observed by Raman scattering,and mid-infrared luminescence from epitaxial PbTe was observed at a peak of 3.5 ?m of PL.The Hall effect measurement results show that the carrier concentration of the PbTe epitaxial layer is about 5 1017 cm-3,the electron mobility at room temperature is 675 cm2/V.s,and the mobility at 2 K is 4300 cm2/Vs.High-quality PbTe grown on GaAs(211)substrates with CdTe/ZnTe buffer layers has broad application prospects in the fields of optoelectronics and thermoelectrics.(2)X-ray photoelectron spectroscopy(XPS)was used to study the energy band structure of the heterojunction interface formed by MBE grown SnTe and PbTe,and the measured data was used to analyze the arrangement and the factors that influence the arrangement of the energy bands on the heterojunction interface.We reasonably selected the core energy level away from the valence band top and used multiple core energy levels of Pb and Sn to jointly determine the valence band arrangement of the heterojunction.The XPS results show that the band structure is a type ? band structure with a valence band offset of 1.370.18 eV and a conduction band offset of 1.230.18 eV.The results help to understand the carrier transport and energy transfer of the PbTe/SnTe heterojunction interfaces,which is beneficial to the design and improvement of new optoelectronic devices with PbTe/SnTe heterojunctions.(3)MBE was used to grow CdTe/SnTe heterojunction,and XPS was used to determine the energy band structure of CdTe/SnTe(111)heterojunction interface by Kraut method.On the meantime,the valence band offset was further verified by determining the valence band maximum position of the two materials which form this heterojunction by changing the CdTe overlayer thickness.We found that the values from two measurements were consistent The XPS results show that the band structure is an ideal I-type band structure for solar cells,with a valence band offset of 1.330.18 eV and a conduction band offset of 0.090.18 eV.Experimental determination of the band structure of CdTe/SnTe heterojunctions can help improve the photovoltaic performance of CdTe thin film solar cells and facilitate the design and fabrication of other CdTe/SnTe heteroj unction devices.In addition,we combined SnTe into C dTe thin film solar cell as a back contact buffer layer,and it was compared with the battery structure without the SnTe buffer layer.The feasibility of using SnTe as a solar cell back contact is confirmed.On the basis of higher battery stability,the performance of the battery with SnTe buffer layer is close to that of the conventional battery with CuxTe buffer layer and the battery with SnTe buffer layer has a large room for improvement.
Keywords/Search Tags:?-? semiconductor, PbTe, SnTe, molecular beam epitaxy, heterojunction, XPS, band structure, CdTe solar cell
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