Difference in anisotropic etching characteristics of alkaline and copper based acid solutions for single-crystalline Si

The so called inverted pyramid arrays, outperforming conventional upright pyramid textures, have been successfully achieved by one-step Cu assisted chemical etching (CACE) for light reflection minimization in silicon solar cells. Due to the lower reduction potential of Cu(2+)/Cu and different electronic properties of different Si planes, the etching of Si substrate shows orientation-dependent. Different from the upright pyramid obtained by alkaline solutions, the formation of inverted pyramid results from the coexistence of anisotropic etching and localized etching process. The obtained structure is bounded by Si {111} planes which have the lowest etching rate, no matter what orientation of Si substrate is. The Si etching rate and (100)/(111) etching ratio are quantitatively analyzed. The different behaviors of anisotropic etching of Si by alkaline and Cu based acid etchant have been systematically investigated.