8 to about 100 h 2 so 4 h 2 o 2 h 2 o is about 1 8 100 and have an etch rate of about 300 nm min in another example the piranha etch solution may be more dilute and may have a volumetric concentration ratio of sulfuric acid to hydrogen peroxide to water of about 1 to about 8 to about 500 h 2 so 4 h 2 o 2 h 2 o is about 1 8 500 and have an etch rate of about 60 nm min in another example the piranha etch solution may be further diluted and may have a volumetric concentration ratio of sulfuric acid to hydrogen peroxide to water of about 1 to about 8 to about 1 000 h 2 so 4 h 2 o 2 h 2 o is about 1 8 1 000 and have an etch rate of about 30 nm min in another embodiment upper portion 208 of gallium arsenide cell 210 may be exposed to a citric acid etch solution for removing gallium arsenide material disposed within the contact layer but not within a passivation layer containing aluminum arsenide while extending apertures 224 the citric acid etch solution may contain citric acid ammonium hydroxide and hydrogen peroxide.