| Wet etching of slicon substrate enables fabrication of sophisticated patterned silicon substrate?PSiS?for a number of applications,such as solar cells,LED and MEMS devices.PSiS with random or periodical micro/nano structures has been fabricated and extensively used in solar cells to achieve lower reflectivity and higher cell efficiency.However,the detailed anisotropic etching behavior and mechanism of PSiS in the alkaline TMAH solutions were still not well understood.Therefore,in this study,insights into the wet etching behaviors of silicon substrate with circular hole/cylinder SiO2 masks?circular hole/cylinder PSiS?in TMAH solutions of varying concentrations were obtained.The morphological evolutions of circular hole/cylinder PSiS in TMAH solution with different concentrations were studied by controlling TMAH concentration,etching time,and the shape of SiO2 mask.Etching circular hole PSiS in 1 mass%TMAH revealed the widest spectrum of morphological evolutions including the circular-like holes,inverted octahedral frustums,octahedral pyramids,and pyramids;etching in 5–25mass%TMAH revealed the inverted octahedral frustums,pyramidal frustums,and pyramids.In contrast,etching circular cylinder PSiS in 1 mass%TMAH revealed the cone frustums,prismatic stacking structures,and pyramids;etching in 5–15 mass%TMAH revealed the prismatic stacking structures and octagonal pyramids;etching in20–25 mass%TMAH revealed the prismatic stacking structures,pyramidal-prismatic stacking structures,and octagonal pyramids.A series of crystallographic planes formed due to the anisotropic crystallographic etching when the PSiS samples were etched in TMAH solution.The etching rates and Miller indexes of exposed crystallographic planes were accurately determined using SEM and AFM to explain the morphological evolution and anisotropic etching mechanism.Etching circular hole PSiS in TMAH revealed C1-,C2-,C3-,C4-,and C5-pl<sub>an<sub>es,the Miller indexes of which were indexed as—C1{3<sub>40},C2{<sub>110},C3{<sub>11<sub>1},C4{211},and C5{1 14 0}.The etching rates of C1-,C2-,and C3-planes increased with the increase of TMAH concentration,while the etching rates of C5-and?100?planes decreased with the increase of TMAH concentration.When circular cylinder PSiS was etched in TMAH solution,P1-,P2-,P3-,P4-,and P5-planes were exposed,the Miller indexes of which were indexed as—P1{221<sub>},P2{11<sub>1},P3{1<sub>31<sub>},P4{131<sub>},and P5{140}.The etching rates of P1-and P3-planes increased firstly and then decreased with the increase of TMAH concentration,while the etching rates P4-and P5-planes decreased with the increase of TMAH concentration.This work contributes to the controllable fabrication of sophisticated silicon microstructures for Si-based optoelectronic devices with potentially enhanced performance. |
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