2-in-1 red-/green-/blue sensitive a-SiC:H/a-Si:H/a-SiGeC:H thin film photo detector with an integrated optical filter

This paper presents an inventive unipolar amorphous silicon (a-Si:H) two terminal two color photo sensor, featuring two functional modes of operation. The sensor structure is green sensitive at - 8.5 V and reaches a sensitivity maximum of 130 mA/W. At lower absolute bias voltage values the spectral response at 550 nm is suppressed by an internal optical filter. The filter structure consists of an a-Si:H/a-SiGeC:H absorber interface, generating an interior trapping area with high defect densities. The combination of an internal band gap barrier and an area with high defect states causes localized charge recombination. The interface deteriorates transport properties locally to suppress green sensitivity while the detectors blue and red efficiencies exceed. The maximum suppression of the 530 nm response is 32.5 mA/W at - 5.5 V bias voltage. Additionally, we observe a shift of both two color sensitivity maxima. The peak at lower wavelength shifts from 350 nm to 480 nm. In consequence, the device is even able to detect signals in the near ultraviolet spectrum. The second peak shifts from 590 nm to 640 nm. At - 8.5 V the filter is deactivated and the maximum detector response is located at 530 nm. In reverse biased conditions the device's dynamic range remains constantly high and reaches values of 90 dB at 1000 lx white-light illumination. The interior 85 nm a-Si:H layer reduces the dark current density to 10(-8) A/cm(2) at - 8 V. Possible sensor applications may exist in fields of medical diagnostics, fluorescence and spectrophotometrical measurements, chemical analysis or in colorimetric and hyperspectral imagery. (C) 2013 Elsevier B.V. All rights reserved.