TY - GEN
T1 - Molecular Beam Epitaxy Growth of CdSe for Si-based Tandem Cell Application
AU - Schaefer, Stephen
AU - Ju, Zheng
AU - McMinn, Allison
AU - Qi, Xin
AU - Zhang, Yong Hang
N1 - Funding Information:
ACKNOWLEDGMENT This work is partly supported by the NSF I/UCRC SPF2050 (Award number: IIP-2052814) and First Solar. The authors acknowledge the use of facilities within the Eyring Materials Center at Arizona State University supported in part by NNCI-ECCS-2025490.
Publisher Copyright:
© 2022 IEEE.
PY - 2022
Y1 - 2022
N2 - The II-VI compound semiconductor CdSe has a bandgap energy of 1.71 eV [1] and 1.68 eV [2] in the wurtzite (hexagonal) and zincblende (cubic) crystal structures, respectively, making it an ideal candidate material for the top cell in tandem application with a Si bottom cell. However, the growth of monocrystalline CdSe and control of its phase, wurtzite or zincblende, remains a challenge. Molecular beam epitaxy (MBE) growth of CdSe thin films nearly lattice matched to InAs (100), (111)A, and (111)B oriented substrates is investigated. Growth temperature ranges from 250 to 350 °C, Cd/Se flux ratio ranges from 0.74 to 1.35, and the growth rate ranges from 0.14 to 0.84 monolayers per second. Single crystal zincblende material luminescing at 1.668 eV is demonstrated on the (100) substrates, while polycrystalline mixed-phase material luminescing from 1.589 to 1.726 eV is demonstrated on the (111) substrates. In-situ reflection high energy electron diffraction (RHEED) patterns show a clear transition from zincblende 1 times 1 surface reconstructions with four-fold symmetry to wurtzite 1 times 1 reconstructions with six-fold symmetry. The results indicate that CdSe crystal phase and thin film morphology is highly sensitive to growth temperature, Cd/Se flux ratio, and polar (111) surface preparation.
AB - The II-VI compound semiconductor CdSe has a bandgap energy of 1.71 eV [1] and 1.68 eV [2] in the wurtzite (hexagonal) and zincblende (cubic) crystal structures, respectively, making it an ideal candidate material for the top cell in tandem application with a Si bottom cell. However, the growth of monocrystalline CdSe and control of its phase, wurtzite or zincblende, remains a challenge. Molecular beam epitaxy (MBE) growth of CdSe thin films nearly lattice matched to InAs (100), (111)A, and (111)B oriented substrates is investigated. Growth temperature ranges from 250 to 350 °C, Cd/Se flux ratio ranges from 0.74 to 1.35, and the growth rate ranges from 0.14 to 0.84 monolayers per second. Single crystal zincblende material luminescing at 1.668 eV is demonstrated on the (100) substrates, while polycrystalline mixed-phase material luminescing from 1.589 to 1.726 eV is demonstrated on the (111) substrates. In-situ reflection high energy electron diffraction (RHEED) patterns show a clear transition from zincblende 1 times 1 surface reconstructions with four-fold symmetry to wurtzite 1 times 1 reconstructions with six-fold symmetry. The results indicate that CdSe crystal phase and thin film morphology is highly sensitive to growth temperature, Cd/Se flux ratio, and polar (111) surface preparation.
KW - CdSe
KW - II-VI
KW - molecular beam epitaxy
KW - photovoltaic
KW - tandem cell
KW - thin film
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U2 - 10.1109/PVSC48317.2022.9938810
DO - 10.1109/PVSC48317.2022.9938810
M3 - Conference contribution
AN - SCOPUS:85142772657
T3 - Conference Record of the IEEE Photovoltaic Specialists Conference
SP - 1288
EP - 1290
BT - 2022 IEEE 49th Photovoltaics Specialists Conference, PVSC 2022
PB - Institute of Electrical and Electronics Engineers Inc.
T2 - 49th IEEE Photovoltaics Specialists Conference, PVSC 2022
Y2 - 5 June 2022 through 10 June 2022
ER -