Formation of nanoporous InP in KOH and KCl: electrochemistry and electron microscopy

This thesis focuses on electrochemical pore formation in n-InP in KOH. A model for pore growth along the <111>A crystallographic directions was previously developed in our group. It is shown how an understanding of this model can be used to explain the main features of a linear sweep voltammogram of InP in KOH. A computational model of <111>A pore growth is demonstrated. It reproduces the experimentally observed cross sections of porous domains and qualitatively reproduces many other features of porous layer etching. The effect of current density on porous layer etching is investigated. It is shown that mass transport through a surface pit is a key factor limiting porous layer thickness. It is also shown that crystallographic pore etching in InP in KOH is most likely a sixelectron process. The effect of temperature and KOH concentration on porous layer etching is also investigated. A current-line oriented pore morphology is observed at low temperatures in both the highest and lowest KOH concentrations in which pore growth is observed. The variation of pore width with both temperature and concentration, as well as the formation of current-line oriented pores is explained in terms of a model of charge transfer at the semiconductor/electrolyte interface. Porous layers are also formed in KCl, and these are compared with those formed in KOH. These KCl porous layers grow to much greater thicknesses and the pore walls are crystallographically bounded. It is argued that the premature cessation of porous layer etching in KOH is caused by the formation of an insoluble indium oxide during the etching process. This oxide blocks the passage of reactants to the pore tips. Finally, it is argued that the utility of porous etching in KOH is in its unique ability to elucidate the mechanisms of purely electrochemical porous etching.