[16p-304-1~13] Photovoltaic 4.0 －高効率・低コスト太陽光発電がもたらす次世代再生可能エネルギーシステム－

▲ [16p-304-5] Fabrication of p-i-n GaAs solar cells grown by hydride vapor phase epitaxy

〇Oshima Ryuji¹、Makita Kikuo¹、Ubukata Akinori²、Sugaya Takeyoshi¹ (1.AIST、2.TNSC)

キーワード：Solar cells, III-V semiconductors, Hydride vapor phase epitaxy

To date, highly efficient III-V multi-junction solar cells are limited to both space and terrestrial high-concentration systems due to their extremely expensive manufacturing costs. Our target is to develop low costs, high throughput growth techniques for the implementation of large scale terrestrial III-V/Si modules with low-concentration (up to 10 suns) systems [1]. In particular, hydride vapor phase epitaxy (H-VPE), in contrast with metal-organic vapor phase epitaxy, can attain significantly high growth rates (~100 mm/h), and enables very low material costs by replacing the expensive metal-organic sources with cheaper elemental Group III metals. This work focuses on the growth of simple p-i-n GaAs homojunction solar cells grown by H-VPE with a horizontal reactor design. A p-i-n GaAs solar cell was grown on p-type GaAs(001) just substrates in a custom-build, atmospheric pressure, horizontal, hot wall reactor. Two growth chamber and a preparation chamber are utilized in a quartz tube to form abrupt junctions through mechanical transfer of the wafer between each chamber. A source and a substrate region are independently heated at 850 °C and 710 °C, respectively. Gaseous HCl in a H₂ carrier is introduced to react with liquid Ga and In contained within quartz boats resulting in the formation of GaCl and InCl, while the AsH₃ was used for group V transport agents. Growth rate for the GaAs was ~8 mm/h with a HCl flow of 5.0 sccm, while V/III ratio was 5~10. From SIMS measurements, a relatively narrow transition depth of less than 40 nm was obtained for doped layers using DEZn or H₂S. In I-V measurements under AM1.5G at 1 sun, in spite of the lack of window and back surface field layers, we were able to obtain J_SC of 11.6 mA/cm² without an anti-reflection coating and V_OC of 0.90 V with our low-cost H-VPE, which are very comparable with results for H-VPE grown GaAs solar cells without any passivation layers reported previously by J. Simon et al. [2]. Dark current measurements showed an ideality factor of 1.34 at the J_SC point. Consequently, the conversion efficiency of 8.57% was obtained. [1] K. Makita et. al, 26th PVSEC, 1.2.3b (2016, Singapore). [2] J. Simon et al., J. Photovolt. 6, 191 (2016).