skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells

Abstract

Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what wemore » expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.« less

Authors:
; ; ; ;  [1]; ; ;  [2]; ; ; ;  [3]; ;  [4]
  1. Department of Physics, Imperial College, London SW7 2BZ (United Kingdom)
  2. Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79110 Freiburg (Germany)
  3. Department of Electrical Engineering and Information Systems, The University of Tokyo, Tokyo (Japan)
  4. CNR-IMEM Sezione di Parma, Parco Area delle Scienze 37/A, 43010 Fontanini-Parma (Italy)
Publication Date:
OSTI Identifier:
22310978
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION; ANISOTROPY; ASYMMETRY; CURRENTS; GALLIUM ARSENIDES; ILLUMINANCE; INDIUM COMPOUNDS; LAYERS; LIFETIME; NANOWIRES; PHOSPHORUS COMPOUNDS; PHOTOLUMINESCENCE; QUANTUM EFFICIENCY; QUANTUM WELLS; QUANTUM WIRES; SOLAR CELLS; SUBSTRATES; TIME RESOLUTION; TRANSMISSION ELECTRON MICROSCOPY; VISIBLE RADIATION

Citation Formats

Alonso-Álvarez, D., Thomas, T., Führer, M., Hylton, N. P., Ekins-Daukes, N. J., Lackner, D., Philipps, S. P., Bett, A. W., Sodabanlu, H., Fujii, H., Watanabe, K., Sugiyama, M., Nasi, L., and Campanini, M.. InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells. United States: N. p., 2014. Web. doi:10.1063/1.4894424.
Alonso-Álvarez, D., Thomas, T., Führer, M., Hylton, N. P., Ekins-Daukes, N. J., Lackner, D., Philipps, S. P., Bett, A. W., Sodabanlu, H., Fujii, H., Watanabe, K., Sugiyama, M., Nasi, L., & Campanini, M.. InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells. United States. doi:10.1063/1.4894424.
Alonso-Álvarez, D., Thomas, T., Führer, M., Hylton, N. P., Ekins-Daukes, N. J., Lackner, D., Philipps, S. P., Bett, A. W., Sodabanlu, H., Fujii, H., Watanabe, K., Sugiyama, M., Nasi, L., and Campanini, M.. Mon . "InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells". United States. doi:10.1063/1.4894424.
@article{osti_22310978,
title = {InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells},
author = {Alonso-Álvarez, D. and Thomas, T. and Führer, M. and Hylton, N. P. and Ekins-Daukes, N. J. and Lackner, D. and Philipps, S. P. and Bett, A. W. and Sodabanlu, H. and Fujii, H. and Watanabe, K. and Sugiyama, M. and Nasi, L. and Campanini, M.},
abstractNote = {Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.},
doi = {10.1063/1.4894424},
journal = {Applied Physics Letters},
number = 8,
volume = 105,
place = {United States},
year = {Mon Aug 25 00:00:00 EDT 2014},
month = {Mon Aug 25 00:00:00 EDT 2014}
}
  • To investigate the effect of the miniband formation on the optical absorption spectrum, we adopted two non-destructive methodologies of piezoelectric photothermal (PPT) and photoreflectance (PR) spectroscopies for strain-balanced InGaAs/GaAsP multiple quantum-well (MQW) and superlattice (SL) structures inserted GaAs p-i-n solar cells. Because the barrier widths of the SL sample were very thin, miniband formations caused by coupling the wave functions between adjacent wells were expected. From PR measurements, a critical energy corresponding to the inter-subband transition between first-order electron and hole subbands was estimated for MQW sample, whereas two critical energies corresponding to the mini-Brillouin-zone center (Γ) and edge (π)more » were obtained for SL sample. The miniband width was calculated to be 19 meV on the basis of the energy difference between Γ and π. This coincided with the value of 16 meV calculated using the simple Kronig–Penney potential models. The obtained PPT spectrum for the SL sample was decomposed into the excitonic absorption and inter-miniband transition components. The latter component was expressed using the arcsine-like signal rise corresponding to the Γ point in the mini-Brillouin zone that was enhanced by the Sommerfeld factor. The usefulness of the PPT methodology for investigating the inserted MQW and/or SL structure inserted solar cells is clearly demonstrated.« less
  • Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) and radiative and non-radiative carrier recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although the optical absorbance signal intensity was proportional to the number of QW stack, the signal intensities of the SPV and PPT methods decreased at high number of stack. To explain the temperature dependency of these signal intensities, we proposed a model that considers the three carrier dynamics: the thermal escape from the QW, and the non-radiativemore » and radiative carrier recombinations within the QW. From the fitting procedures, it was estimated that the activation energies of the thermal escape ΔE{sub barr} and non-radiative recombination ΔE{sub NR} were 68 and 29 meV, respectively, for a 30-stacked MQW sample. The estimated ΔE{sub barr} value agreed well with the difference between the first electron subband and the top of the potential barrier in the conduction band. We found that ΔE{sub barr} remained constant at approximately 70 meV even with increasing QW stack number. However, the ΔE{sub NR} value monotonically increased with the increase in the number of stack. Since this implies that non-radiative recombination becomes improbable as the number of stack increases, we found that the radiative recombination probability for electrons photoexcited within the QW increased at a large number of QW stack. Additional processes of escaping and recapturing of carriers at neighboring QW were discussed. As a result, the combination of the three non-destructive methodologies provided us new insights for optimizing the MQW components to further improve the cell performance.« less
  • The effects of growth temperature on the properties of InGaAs/GaAsP multiple quantum well (MQW) solar cells on various mis-orientated GaAs substrates were studied using metalorganic vapor phase epitaxy. Thickness modulation effect caused by mismatch strain of InGaAs/GaAsP could be suppressed by low growth temperature. Consequently, abrupt MQWs with strong light absorption could be deposited on mis-oriented substrates. However, degradation in crystal quality and impurity incorporation are the main drawbacks with low temperature growth because they tend to strongly degraded carrier transport and collection efficiency. MQW solar cells grown at optimized temperature showed the better conversion efficiency. The further investigation shouldmore » focus on improvement of crystal quality and background impurities.« less
  • We have investigated the properties of multi-stacked layers of self-organized In{sub 0.4}Ga{sub 0.6}As quantum dots (QDs) on GaAs (311)B grown by molecular beam epitaxy. We found that a high degree of in-plane ordering of QDs structure with a six-fold symmetry was maintained though the growth has been performed at a higher growth rate than the conventional conditions. The dependence of photoluminescence characteristics on spacer layer thickness showed an increasing degree of electronic coupling between the stacked QDs for thinner spacer layers. The external quantum efficiency for an InGaAs/GaAs quantum dot solar cell (QDSC) with a thin spacer layer thickness increasedmore » in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. Furthermore, a photocurrent production by 2-step photon absorption has been observed at room temperature for the InGaAs/GaAs QDSC with a spacer layer thickness of 15 nm.« less
  • No abstract prepared.