Tailored Laser scanned photodiodes (LSP) for image recognition
- PDF / 224,363 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 32 Downloads / 157 Views
Tailored Laser scanned photodiodes (LSP) for image recognition 1*
M. Vieira ,1M. Fernandes, 1P. Louro, 1Y. Vygranenko, 1R. Schwarz, and 2M. Schubert Electronics and Communications Dept., ISEL, R. Conselheiro Emídio Navarro, P 1949-014 Lisboa, Portugal. 2 Institut fur Physikalische Elektronik, Pfaffenwaldring 47, D-70569 Stuttgart, Germany. 1
ABSTRACT A tailored ZnO:Al/a-p-i-n SiC:H/Al configuration for the laser scanned photodiode (LSP) imaging detector is proposed. The LSP utilizes light modulated depletion layers as detector and a laser beam for readout. When highly resistive a-SiC:H doped layers are used its higher optical gap when compared with the active layer are responsible by charge accumulation at the illuminated interfaces which blocks the carrier collection under illumination. Those insulator-like layers act as MIS structures that prevent excess signal charge from blooming to the nearby dark regions avoiding the image smearing. The optical-to-electrical transfer characteristics show reciprocity between light intensity and image signal intensity only limited by the doped layers composition. Data reveal that the sensitivity, the responsivity and the spatial resolution are limited by the cell configuration while the linearity depends on the light source flux used to map the image onto the sensor. By using tailored SiC:H/Si:H/SiC:H p-i-n heterostructures an increase in the image signal optimized to the blue is achieved with a responsivity of 0.2 mW/cm2 and a spatial resolution of 20 µm. INTRODUCTION Whenever we wish to view images or count photons, we use devices that work by absorbing photons and turning them into information. Any conventional solid state imaging device consists of an array of sensing elements combined with some form of transport mechanism to deliver the sensor output signal to the periphery of the device. Sensors used in commercial devices include photodiode arrays [1], charge-coupled devices (CCD) [2], complementary metal oxide semiconductors (CMOS) [3], and charge injecting devices (CID) [4]. All of these devices use essentially the same light sensing mechanism. Photons penetrating a depletion region generate electron-hole pairs. These carriers are swept away by the electric field across the depletion region and generate a small transverse photocurrent. It is known that a light pattern projected onto a semiconductor junction leads to a distortion of space charge regions giving rise to potential barrier modulation that depends on the spatial distribution of the light pattern [5]. Low local potential barriers are ascribed to illuminated regions and high potential barriers to dark zones [6]. Based on this effect, microcrystalline [7] and amorphous [8] optical TCO/p-i-n/metal image transducers were developed. Those sensors are different from the CCD’s since are based on one single sensing element and use a modulated, low-power beam of laser light to acquire the image directly. By using the amorphous silicon technology it is possible to produce large area sensors thus increasing the image ar
Data Loading...
