Self-assembled formation of InP nanopore arrays by electrochemical anodization

High density, uniform arrays of ⟨001⟩-oriented straight nanopores were successfully formed on (001) n-InP surfaces in a self-assembled fashion by electrochemical anodization in 1 M HCl+HNO₃ solution. Unlike porous Si, the pores do not have side branches and possessed nearly equal-sized square-shapes defined by four crystalline flat (110) facets. Preferential etching along vertical ⟨001⟩-direction due to slow etching rates on (110) side facets may be responsible for formation of such a uniform structure. At low temperature, the nanopore arrays showed strong red-shifted photoluminescence (PL) emission probably due to a transition involving a broad surface state continuum at the pore wall surfaces. On the other hand, a strong blue-shifted PL emission was observed at room temperature, confirming presence of quantum size effect in the pore walls as expected from the structural observations