Method and device for wavelength-sensitive photo-sensing

A semiconductor device includes a conducting channel ( 130 ) formed beneath a substrate surface with a pre-determined photo-conductivity spectral response. The channel is formed between two pn-junctions ( 126, 128 ) defining first and third photo-electric depletion regions at respective depths relative to the surface corresponding to penetration depths of light of different wavelengths. The first region ( 106 ) which has the light absorbing surface ( 104 ) above the first pn-junction ( 126 ) is specific to a first colour. The channel region ( 130 ) between the two pn-junctions ( 126, 128 ) is photo-conductive to a second colour. The third region below the second pn-junction ( 128 ) is sensitive to a third colour. Electrical contacts ( 118, 120, 122, 124 ) are disposed on the source ( 112 ), the top gate ( 106 ), the drain ( 114 ) and the bottom gate ( 116 ) for receiving the electrical currents induced by the presence of the absorbed wavelengths.