ABSTRACT
Electrochemically etched pores in n-type III-V semiconductors can be divided into two basic classes according to their appearance and properties: crystallographic pores (crystos) and currentline pores (curros). Crystallographic pores have first been observed in InP using an aqueous HCl electrolyte [1, 2]. Crysto pores always grow into the <111> B direction, independent of the substrate orientation. The pore tips and pore walls are typically facetted; a detailed overview can be found in [3]. In the meantime, crysto pores have also been etched into InP with electrolytes rather diff erent to acidic HCl, e.g., solutions of NaF [4], KOH [5], and NaCl [6], and into other III-V crystals such as GaP (H2SO4 [2], H3PO4 [7],
HNO3 [8], and bromine-based solutions [9]) and GaAs (HCl [2], NaCl [10], HF [11], and H2SO4 [2, 12]). Of course, most pores found in Si and Ge have always been of the crystallographic type without this being mentioned in most publications; cf. [13-15] for details. An example of crystallographic pores in InP is shown in Fig. 1.1a.
