Study Of Cu-assisted Chemical Etching For Fabricating Nano-structured Silicon

Fabrication of black silicon and its application on photovoltaic solar cells is vital for decreasing manufacture cost and increasing conversion efficiency. Metal-assisted chemical etching is springing up as a common technique for fabricating black silicon in recent years. Low cost, simple operation and suitable for large-scale manufacture is its best advantage. This thesis makes improvement on former-used metal-assisted chemical etching technique. We used one-step Cu-assisted chemical etching on polycrystalline silicon and monocrystalline silicon to fabricate black silicon and researched on its reaction mechanism systematically. Our main work include following points:On polycrystalline silicon, we regulate and control its surface morphology by adjusting the concentration of HF, H2O2, Cu(NO3)2 and reaction temperature. The samples achieve their lowest surface reflectance when [H2O2]:[HF]:[Cu(NO3)2]= 2M:6M:0.08M at 60℃.In the wave range of 300nm to 1000nm, the average reflectance is as low as 5%.Besides, we studied the relationships between reaction rates and [H2O2], [HF], [Cu(NO3)2] as well as reaction temperature. We used the "hole injection model" to explain the experimental phenomena.On monocrystalline silicon, we fabricated the reverse pyramid pattern on its surface. The corresponding reflectance also gets as low as 5% in broad wave band. We also compared the differences between Ag-assisted and Cu-assisted chemical etching. The differences are mainly owing to the reduction potential of Ag+/Ag and Cu2+/Cu.