The growth of InGaAs/GaAs quantum dots by MOCVD has been optimized to obtain defect-free solar cell structure. The material and device properties of QDSC structures have been studied, and the 10-layer QD device showed improved photocurrent in comparison to a GaAs control cell. However, the overall efficiency was not improved due to the reduction of open-circuit voltage. The fundamental mechanism for this observation was explored by the investigation of temperature dependent I-V measurements. Especially, we have performed a comparative study on the temperature dependent dark
Chapter 3 Growth and properties of InGaAs/GaAs quantum dot solar cells
77
current properties of GaAs p-i-n reference and InGaAs/GaAs QD solar cells. The QD devices exhibit much more complicated dark I-V behaviour due to the temperature and bias dependent carrier capture, occupation and recombination via QD bound states.
Two-photon absorption has also been investigated for 10-layer QDSC. There is a clear trend that inter-subband photocurrent declines with increasing temperature and cannot be observed at temperatures greater than 70 K. Because at higher temperatures the thermal energy is stronger and thermal transition becomes the dominant excitation path compared to optical excitation (2nd photon excitation).
In addition, QDSCs with different number of QD layers were grown and analyzed. With the increasing number of layers, light absorption in the QD structures is increased however with degraded photocurrent and efficiency, because of non-radiative recombination and poor carrier extraction. EL emission of the solar cell devices under various injection densities was also studied showing that progressive filling of QD states, where the injected carriers fill the states of larger QDs first and then occupy the confined states of smaller dots which have higher ground state energy. This phenomenon implies that the larger size distribution of QDs will result in the non-uniform filling of carriers.
The results obtained in the chapter indicates that further careful design and growth of QDSC is necessary to maximize light absorption while maintaining good carrier extraction and minimization of defect related recombination. It is necessary to provide more carriers occupied in the QD/WL states to improve the photo-generated carrier collection efficiency. A possible effective approach is n-type modulation doping applied within QD layers. The investigation of modulation doping effects on QDSCs will be discussed in Chapter 4.
References
[1] da Silva, M.J., A.A. Quivy, P.P. Gonzalez-Borrero, N.T. Moshegov, and E. Marega, Correlation between structural and optical properties of InAs quantum dots along their evolution.Journal of Crystal Growth, 2001. 227: pp. 1025-1028.
[2] Leon, R. and S. Fafard, Structural and radiative evolution in quantum dots near the InxGa1-xAs/GaAs Stranski-Krastanow transformation. Physical Review B, 1998. 58(4): pp. R1726-R1729.
[3] Sugaya, T., S. Furue, H. Komaki, T. Amano, M. Mori, K. Komori, S. Niki, O. Numakami, and Y. Okano, Highly stacked and well-aligned In0.4Ga0.6As quantum dot solar cells with In0.2Ga0.8As cap layer.Applied Physics Letters, 2010. 97(18): pp. 183104.
Chapter 3 Growth and properties of InGaAs/GaAs quantum dot solar cells
78
[4] Heyn, C. and C. Dumat, Formation and size evolution of self-assembled quantum dots.Journal of Crystal Growth, 2001. 227: pp. 990-994.
[5] Heinrichsdorff, F., A. Krost, M. Grundmann, D. Bimberg, F. Bertram, J. Christen, A. Kosogov, and P. Werner, Self organization phenomena of InGaAs/GaAs quantum dots grown by metalorganic chemical vapour deposition. Journal of Crystal Growth, 1997. 170(1-4): pp. 568-573.
[6] Lever, P., Interdiffusion and Metalorganic Vapour Phase Epitaxial Growth of Self-Assembled InGaAs Quantum Dot Structures and Devices. 2004, Australian National University: Canberra, Australia. pp. 42-51.
[7] Stringfellow, G.B., Organometallic Vapor-Phase Epitaxy: Theory and Practice. 2012: Elsevier Science.
[8] Lever, P., Interdiffusion and Metalorganic Vapour Phase Epitaxial Growth of Self-Assembled InGaAs Quantum Dot Structures and Devices. 2004, Australian National University: Canberra, Australia. pp. 49.
[9] Hubbard, S.M., C. Plourde, Z. Bittner, C.G. Bailey, M. Harris, T. Bald, M. Bennett, D.V. Forbes, and R. Raffaelle. InAs quantum dot enhancement of GaAs solar cells. in Conference Record of the 35th Ieee Photovoltaic Specialists Conference. 2010. New York: IEEE.
[10] Takata, A., R. Oshima, Y. Shoji, K. Akahane, and Y. Okada. Fabrication of 100 layer-stacked InAs/GaNAs strain-compensated quantum dots on GaAs (001) for application to intermediate band solar cell. in Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE. 2010.
[11] Wasilewski, Z.R., S. Fafard, and J.P. McCaffrey, Size and shape engineering of vertically stacked self-assembled quantum dots. Journal of Crystal Growth, 1999. 201–202: pp. 1131-1135.
[12] Okada, Y., N.J. Ekins-Daukes, T. Kita, R. Tamaki, M. Yoshida, A. Pusch, O. Hess, C.C. Phillips, D.J. Farrell, K. Yoshida, N. Ahsan, Y. Shoji, T. Sogabe, and J.F. Guillemoles, Intermediate band solar cells: Recent progress and future directions.Applied Physics Reviews, 2015. 2(2): pp. 021302.
[13] Fu, L., I. McKerracher, H.H. Tan, C. Jagadish, N. Vukmirovic, and P. Harrison, Effect of GaP strain compensation layers on rapid thermally annealed InGaAs/GaAs quantum dot infrared photodetectors grown by metal-organic chemical-vapor deposition.Applied Physics Letters, 2007. 91(7): pp. 073515.
[14] Martí, A., N. López, E. Antolín, E. Cánovas, A. Luque, C.R. Stanley, C.D. Farmer, and P. Díaz, Emitter degradation in quantum dot intermediate band solar cells.Applied Physics Letters, 2007. 90(23): pp. 233510.
[15] Jolley, G., H.F. Lu, L. Fu, H.H. Tan, and C. Jagadish, Electron-hole recombination properties of In0.5Ga0.5As/GaAs quantum dot solar cells and the influence on the open circuit voltage.Applied Physics Letters, 2010. 97(12): pp. 123505.
[16] Lu, H.F., L. Fu, J. Greg, T. Hark Hoe, T. Sudersena Rao, and J. Chennupati, Temperature dependence of dark current properties of InGaAs/GaAs quantum dot solar cells.Applied Physics Letters, 2011. 98(18): pp. 183509.
[17] Lever, P., Interdiffusion and Metalorganic Vapour Phase Epitaxial Growth of Self-Assembled InGaAs Quantum Dot Structures and Devices. 2004, Australian National University: Canberra, Australia. pp. 24.
Chapter 3 Growth and properties of InGaAs/GaAs quantum dot solar cells
79
[18] Gupta, J.A., S.P. Watkins, E.D. Crozier, J.C. Woicik, D.A. Harrison, D.T. Jiang, I.J. Pickering, and B.A. Karlin, Layer perfection in ultrathin InAs quantum wells in GaAs(001).Physical Review B, 2000. 61(3): pp. 2073-2084.
[19] Yu, P.R., K. Zhu, A.G. Norman, S. Ferrere, A.J. Frank, and A.J. Nozik, Nanocrystalline TiO2 solar cells sensitized with InAs quantum dots. Journal of Physical Chemistry B, 2006. 110(50): pp. 25451-25454.
[20] Sears, K., Growth and Characterisation of Self-Assembled InAs/GaAs Quantum Dots and Optoelectronic Devices. 2006, Australian National University: Canberra, Australia. pp. 95-96.
[21] Rai, R. and C. Parsons, Characterizing III–V heteroepitaxial structures. JOM Journal of the Minerals Metals and Materials Society, 1994. 46(9): pp. 50-54.
[22] Hubbard, S.M., C.D. Cress, C.G. Bailey, R.P. Raffaelle, S.G. Bailey, and D.M. Wilt, Effect of strain compensation on quantum dot enhanced GaAs solar cells. Applied Physics Letters, 2008. 92(12): pp. 123512.
[23] Popescu, V., G. Bester, M.C. Hanna, A.G. Norman, and A. Zunger, Theoretical and experimental examination of the intermediate-band concept for strain- balanced (In,Ga)As/Ga(As,P) quantum dot solar cells.Physical Review B, 2008.
78(20): pp. 17.
[24] Okada, Y., R. Oshima, and A. Takata, Characteristics of InAs/GaNAs strain- compensated quantum dot solar cell. Journal of Applied Physics, 2009. 106(2): pp. 024306.
[25] Ekins-Daukes, N.J., K.W.J. Barnham, J.P. Connolly, J.S. Roberts, J.C. Clark, G.
Hill, and M. Mazzer, Strain-balanced GaAsP/InGaAs quantum well solar cells.
Applied Physics Letters, 1999. 75(26): pp. 4195-4197.
[26] Aperathitis, E., C.G. Scott, D. Sands, V. Foukaraki, Z. Hatzopoulos, and P. Panayotatos, Effect of temperature on GaAs/AlGaAs multiple quantum well solar cells. Materials Science and Engineering B-Solid State Materials for Advanced Technology, 1998. 51(1-3): pp. 85-89.
[27] Radziemska, E., Effect of temperature on dark current characteristics of silicon solar cells and diodes. International Journal of Energy Research, 2006. 30(2): pp. 127-134.
[28] Kachare, R., B.E. Anspaugh, and G.F.J. Garlick, Tunneling effects in the current-voltage characteristics of high-efficiency GaAs solar cells. Solid-State Electronics, 1988. 31(2): pp. 159-166.
[29] Ryzhii, V., I. Khmyrova, V. Pipa, V. Mitin, and M. Willander, Device model for quantum dot infrared photodetectors and their dark-current characteristics. Semiconductor Science and Technology, 2001. 16(5): pp. 331-338.
[30] Schroder, D.K., Semiconductor Material and Device Characterization, 3rd ed., in Semiconductor Material and Device Characterization, 3rd ed. 2006, Wiley: New Jersey.
[31] Kavasoglu, N., A.S. Kavasoglu, and S. Oktik, A new method of diode ideality factor extraction from dark I-V curve.Current Applied Physics, 2009. 9(4): pp. 833-838.
[32] Gu, T.Y., M.A. El-Emawy, K. Yang, A. Stintz, and L.F. Lester, Resistance to edge recombination in GaAs-based dots-in-a-well solar cells. Applied Physics Letters, 2009. 95(26): pp. 261106.
Chapter 3 Growth and properties of InGaAs/GaAs quantum dot solar cells
80
[33] Luque, A. and A. Marti, Increasing the efficiency of ideal solar cells by photon induced transitions at intermediate levels.Physical Review Letters, 1997. 78(26): pp. 5014-5017.
[34] Ley, M., J. Boudaden, and Z.T. Kuznicki, Thermodynamic efficiency of an intermediate band photovoltaic cell with low threshold Auger generation. Journal of Applied Physics, 2005. 98(4): pp. 044905.
[35] Shockley, W. and H.J. Queisser, Detailed Balance Limit of Efficiency of P-N Junction Solar Cells.Journal of Applied Physics, 1961. 32(3): pp. 510-519.
[36] Araújo, G.L. and A. Martí, Absolute limiting efficiencies for photovoltaic energy conversion. Solar Energy Materials and Solar Cells, 1994. 33(2): pp. 213-240.
[37] Marti, A., L. Cuadra, and A. Luque. Quantum dot intermediate band solar cell. in 28th IEEE Photovoltaic Specialists Conference. 2000. Anchorage.
[38] Aroutiounian, V., S. Petrosyan, A. Khachatryan, and K. Touryan, Quantum dot solar cells.Journal of Applied Physics, 2001. 89(4): pp. 2268-2271.
[39] Laghumavarapu, R.B., M. El-Emawy, N. Nuntawong, A. Moscho, L.F. Lester, and D.L. Huffaker, Improved device performance of InAs/GaAs quantum dot solar cells with GaP strain compensation layers.Applied Physics Letters, 2007.
91(24): pp. 243115.
[40] Guimard, D., R. Morihara, D. Bordel, K. Tanabe, Y. Wakayama, M. Nishioka, and Y. Arakawa, Fabrication of InAs/GaAs quantum dot solar cells with enhanced photocurrent and without degradation of open circuit voltage.Applied Physics Letters, 2010. 96(20): pp. 203507.
[41] Levy, M.Y. and C. Honsberg, Intraband absorption in solar cells with an intermediate band.Journal of Applied Physics, 2008. 104(11): pp. 113103.
[42] Luque, A. and A. Marti, The Intermediate Band Solar Cell: Progress Toward the Realization of an Attractive Concept.Advanced Materials, 2010. 22(2): pp. 160- 174.
[43] Marti, A., E. Antolin, C.R. Stanley, C.D. Farmer, N. Lopez, P. Diaz, E. Canovas, P.G. Linares, and A. Luque, Production of Photocurrent due to Intermediate-to- Conduction-Band Transitions: A Demonstration of a Key Operating Principle of the Intermediate-Band Solar Cell. Physical Review Letters, 2006. 97(24): pp. 247701.
[44] Okada, Y., T. Morioka, K. Yoshida, R. Oshima, Y. Shoji, T. Inoue, and T. Kita, Increase in photocurrent by optical transitions via intermediate quantum states in direct-doped InAs/GaNAs strain-compensated quantum dot solar cell.Journal of Applied Physics, 2011. 109(2): pp. 024301.
[45] Jolley, G., L. Fu, H.F. Lu, H.H. Tan, and C. Jagadish, The role of intersubband optical transitions on the electrical properties of InGaAs/GaAs quantum dot solar cells.Progress in Photovoltaics: Research and Applications, 2013. 21(4): pp. 736-746.
[46] Jolley, G., H.F. Lu, L. Fu, H.H. Tan, and C. Jagadish, Electron-hole recombination properties of In0.5Ga0.5As/GaAs quantum dot solar cells and the influence on the open circuit voltage.Applied Physics Letters, 2010. 97(12): pp. 123505.
[47] Antolin, E., A. Marti, C.D. Farmer, P.G. Linares, E. Hernandez, A.M. Sanchez, T. Ben, S.I. Molina, C.R. Stanley, and A. Luque, Reducing carrier escape in the
Chapter 3 Growth and properties of InGaAs/GaAs quantum dot solar cells
81
InAs/GaAs quantum dot intermediate band solar cell. Journal of Applied Physics, 2010. 108(6): pp. 064513.
[48] Ramey, S.M. and R. Khoie, Modeling of multiple-quantum-well solar cells including capture, escape, and recombination of photoexcited carriers in quantum wells. Ieee Transactions on Electron Devices, 2003. 50(5): pp. 1179- 1188.
[49] Tsai, C.Y. and C.Y. Tsai, Effects of Carrier Escape and Capture Processes on Quantum Well Solar Cells. Nusod '08: Proceedings of the 8th International Conference on Numerical Simulation of Optoelectronic Devices, 2008: pp. 79- 80
Chapter 4 Investigation of modulation doping in quantum dot solar cells
83