Acoustic spalling is a promising technique for substrate reuse in the fabrication of gallium arsenide (GaAs) photovoltaic cells. However, the acoustic spalling process can leave the substrate with areas of rough surface morphology that can interfere with subsequent cell growth and processing. In this work, we investigate the use of wet etchants to smooth the surface of acoustically spalled GaAs substrates. We evaluated six different etchants. Of those tested, an 8:1:1 mixture of sulfuric acid, hydrogen peroxide, and water at 30 $^{\circ }$ C and a moderate stirring rate showed the greatest roughness reduction per mass loss while producing the desired morphology. This etchant was then applied to an acoustically spalled 2-inch GaAs wafer. A single-junction GaAs cell was then grown via metalorganic vapor-phase epitaxy on this substrate, an acoustic spalled substrate without a smoothing etch, and an epi-ready substrate. Use of the 8:1:1 $\mathrm{H_{2}SO_{4}}\hbox{:}\mathrm{H_{2}O_{2}}\hbox{:}\mathrm{H_{2}O}$ etchant produced cells an average efficiency of 12.8% as compared to that of 2.0% grown on the unetched acoustically spalled substrate and 16.3% grown on the epi-ready substrate. The results of this work demonstrate that wet etching is a viable method for smoothing the surface of spalled GaAs substrates, paving the way for substrate reuse via acoustic spalling at efficiencies that approach growth on epi-ready substrates.

中文翻译：

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用于基板再利用的声学剥落 GaAs 湿法蚀刻

声学剥落是砷化镓 (GaAs) 光伏电池制造中基板重复利用的一种很有前途的技术。然而，声学剥落过程可能会在基底上留下粗糙表面形态的区域，从而干扰后续的细胞生长和加工。在这项工作中，我们研究了使用湿法蚀刻剂来平滑声学剥落的 GaAs 基板的表面。我们评估了六种不同的蚀刻剂。在这些测试中，硫酸、过氧化氢和水的 8:1:1 混合物在 30$^{\circ }$ C和适度的搅拌速率显示出单位质量损失的最大粗糙度降低，同时产生所需的形态。然后将该蚀刻剂施加到声学剥落的 2 英寸 GaAs 晶片上。然后通过金属有机气相外延在该基板、未经平滑蚀刻的声学剥落基板和外延就绪基板上生长单结 GaAs 电池。使用8:1:1$\mathrm{H_{2}SO_{4}}\hbox{:}\mathrm{H_{2}O_{2}}\hbox{:}\mathrm{H_{2}O}$与在未蚀刻声学剥落基板上生长的 2.0% 和在外延就绪基板上生长的 16.3% 相比，蚀刻剂生产的电池平均效率为 12.8%。这项工作的结果表明，湿法蚀刻是一种平滑剥落 GaAs 衬底表面的可行方法，为通过声学剥落重复使用衬底铺平了道路，其效率接近于外延衬底上的生长。