Fine-Tuning of the Spectral Collection Efficiency in a Multilayer Junction Through the LSP Technique
- PDF / 85,462 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 32 Downloads / 202 Views
J8.3.1
Fine-tuning of the spectral collection efficiency in a multilayer junction through the LSP technique M. Fernandes1, A. Fantoni1, M. Niehus, P. Louro1, G. Lavareda2, C. N. Carvalho2, M. Vieira1 1 Electronics Telecommunications and Computer Dept., ISEL, R. Conselheiro Emidio Navarro, 1949-014 Lisbon, Portugal, [email protected] 2 CFM-UTL, Av Rovisco Pais, Lisbon, Portugal.
ABSTRACT We report in this paper the recent advances we obtained in optimizing a color image sensor based on the LSP technique. A device structure based on a a-SiC:H/ a-Si:H pin/pin tandem structure has been tested for a proper color separation process that takes advantage on the different filtering properties due to the different light penetration depth at different wavelengths inside the a-Si:H and a-SiC:H absorbers. Under reverse bias the green and the red images give, in comparison with previous tested structures, a weak response, while this structure shows a very good recognition of blue color, leaving a good margin for future device optimization in order to achieve a complete and satisfactory RGB image mapping. The physics behind the device functioning is explained by recurring to a numerical simulation of the internal electrical configuration of the device in dark and under different wavelength irradiations. Considerations about conduction band offsets, electrical field profiles and inversion layers will be taken into account to explain the optical and voltage bias dependence of collected photocurrent.
INTRODUCTION A black and white image sensor based on the measure of the photocurrent perturbation caused by a laser spot over an image projected on the device surface has been presented. In this sensor the image to acquire is optically mapped onto the sensing photodiode and a low-power light spot scans the device by the opposite side. The photocurrent generated by the moving spot is recorded as the image signal, and its magnitude depends on the light pattern localization and intensity Called Laser Scanned Photodiode (LSP) this sensor has recently shown its potential capability as monochrome image sensing devices [1,2]. The LSP under short circuit is naturally monochromatic. For simultaneous light intensity and color detection, the wavelength filtering property of a-SiC:H (variation of the absorption coefficient with wavelength) can be combined with the asymmetric behavior of the photocurrent profile we observed in tandem structures. Photogeneration from a laser scanner can be tuned to compensate the asymmetry in the photogeneration profile, producing a peak on the resulting photocurrent. The physics behind the device operation is explained by recurring to a numerical simulation of the internal electrical configuration of the device in dark and under different wavelength irradiations. Considerations about the internal electric configuration will be taken into account to explain the dependence of the output produced by the color sensor on the optical and voltage bias. Our interpretation point out the cause of such dependence to be a self b
Data Loading...
