Electrochemical formation of uniform and straight nano-pore arrays on (001) InP surfaces and their photoluminescence characterizations

Recently, (001)-oriented nanometer-sized pores (nano-pores) without side br anches, unlike porous Si, have been realized by our group on (001) n-InP su rfaces by means of electrochemical anodization in 1M HCl solution. However, they exhibit large structural nonuniformity including the presence of an i rregular top layer, random pore positioning and wavy pore walls. In this st udy, attempts have been made to improve pore uniformity and to clarify thei r optical properties. Anodization in 1M HCl + HNO3 solution realized highly uniform nano-pore arrays consisting of square-shaped straight pores define d by four crystalline (011) facets. This improvement is explained in terms of preferential etching along the vertical (001)-direction at the pore tip due to the slow etching rate along the lateral (011)-direction as well as t he uniform supply of reactant species to pore tips realized by the removal of the irregular top layer during the anodization process. The nano-pore ar rays show strong blue- and red-shifted photoluminescence emissions at high and low temperatures, respectively. These are assigned as emissions due to the transition between electron and hole quantum states inside the pore wal ls and that involving a broad surface state continuum at pore wall surfaces , respectively.