A method for locally controlling an electrical potential of a semiconductor structure or device, and thus locally controlling lateral and/or vertical photoelectrochemical (PEC) etch rates.
PEC etching uses above-bandgap illumination to generate carriers (specifically holes) needed to etch III-nitrides. The electrochemical potential of the semiconductor material surface relative to the electrolyte causes holes to be drawn toward the semiconductor-electrolyte interface in n-type (unintentionally-doped or doped) material, allowing them to participate in the electrochemical reactions necessary for material removal. Because the etching mechanism relies heavily on the absorption of incident light and the electrochemical potential of the semiconductor material relative to the electrolyte, PEC etching can be defect-selective, dopant-selective, and bandgap-selective. Most applications of PEC etching have pertained to vertical etching of the material, either through direct illumination of the material surface, or by illumination through a masking layer. However, specific descriptions of local control of the etch process through modifications of the electrochemical component of etching have not been presented. Previously published and patented techniques that apply to III-nitride PEC etching suffer from certain limitations.
This invention describes a scheme for fabricating III-nitride semiconductor structures wherein a highly selective photo-induced etch is achieved through strategic modification of the local electrochemical potential of the semiconductor structure relative to the electrolyte. This is accomplished through:
PEC etching is a viable method for producing specific geometries in the III-nitride material system, forming three-dimensional structures that would be extremely challenging to produce with gas-phase etching processes or more standard wet chemical etching. The existence of a controlled three-dimensional etch process can give rise to numerous useful device geometries. Specifically, an undercut geometry is desirable in several applications including but not limited to microdisk resonators, air-gap DBRs, semiconductor membranes and cantilevers, electrical and optical apertures, and in substrate removal.
|United States Of America||Issued Patent||7,550,395||06/23/2009||2005-207|
PEC etching, indPEC, indssl