Departmental Bulletin Paper SPV 法を用いた GaAs 歪緩和層挿入 InGaAs/GaAsP系量子井戸太陽電池のキャリア輸送評価

武田, 秀明  ,  中村, 翼  ,  魯, 家男  ,  K, Toprasertpong  ,  杉山, 正和  ,  碇, 哲雄  ,  福山, 敦彦

46pp.89 - 94 , 2017-07-31 , 宮崎大学工学部
We investigated carrier transport properties in three types of strain-balanced InGaAs/GaAsP quantum well solar cells by using the surface photovoltage (SPV) spectroscopy. First absorbing layer was multiple quantum well (MQW) and second was super-lattice (SL). Last one was GaAs-interlayer-inserted SL structure to relax the strain caused by the lattice mismatch. Distinct SPV signals were observed below the GaAs bandgap energy for all samples. In addition, the SPV signal intensities of SL and GaAs-interlayer samples were larger than that of MQW sample. From the computational calculation by using 3-D nano device simulator, the 1st quantum level of electron (e1) in SL sample and 2nd quantum level of electron (e2) and 1st quantum level of light hole (lh1) in GaAs-interlayer sample were found to form minibands because of the overlapping of wave functions. In these case, carriers can transport by tunneling through minibands without recombination. Since the SPV detects the surface potential change caused by carrier collection, large SPV signals obtained for SL and GaAs-interlayer samples represented that the carrier transport properties were improved by the formation of miniband. On the other hand, the SPV spectrum of SL sample showed two distinctive peaks corresponding to the mini-Brillouin zone center and edge of e2-miniband. The usefulness of SPV for investigating the carrier transport properties in quantum well solar cells was clearly demonstrated.

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