Dissertation - FTP Directory Listing - University of Surrey

1000Number of Pixels1001013000 3500 4000 4500 5000 5500Pixel Value [DN]Figure 4.23 Histogram of dark pixel values for hard reset operationFrom Figure 4.23 it can be seen there is quite a large range of pixel values in the dark, the FWHM isapproximately 400 DN. The noise of LAS was found to be 47e- operating in hard reset mode, whichis quite high but this is due to the 3T structure of the pixel as no noise reduction is taking place.From the noise value and the full well capacity the dynamic range of the sensor can be found, theresults give a dynamic range of 63.3dB.The results for conversion gain, full well capacity, noise and dynamic range agreed quite well withexpected values however the measured quantum efficiency was much lower than expected, thepixels have quite a high fill factor and quantum efficiency was expected to be around 60%. Furthertests on the Aspect system at wavelengths of 470nm and 635nm also showed low QE around 20%.An idea for the cause of this low QE result was that the multiple insulating layers above the substratewere causing a variable level of reflection of incident light dependent on the wavelength. This wouldcause peaks and troughs in QE at different wavelengths, it was postulated that the wavelengthsavailable on the Aspect system all lay in those troughs resulting in a lower QE than expected. To testthis idea more wavelengths needed to be investigated than could be provided by the Aspectsystems, so a second system was set up using a halogen lamp and monochromator to greatlyincrease the wavelengths available, frame capture was performed using an optodaq system. First61