The conventional phenomenological approach describes the response time of semiconductor photodiodes to short laser pulses as time required for collection of non-equilibrium carriers via processes of drift and diffusion. The effect of displacement currents due to dielectric relaxation of majority carriers in the charge-neutral region of semiconductor photodiode is usually neglected. This paper shows that dielectric relaxation of majority carriers may dominate the slow response of not fully depleted photodiodes and has to be taken into account for correct analysis of silicon photodiode response to a brief laser pulse. A phenomenological expression for the photodiode response time that accounts for the displacement current effects is proposed and used to compare with experimental results.
The effect of displacement currents due to dielectric relaxation of majority carriers in the charge-neutral region of a semiconductor photodiode is discussed. The dielectric relaxation is often neglected when treating the response time of photodiodes. We show that this component may dominate the slow response of not fully depleted photodiodes and has to be taken into account for correct analysis of silicon photodiode response to a brief laser pulse. A phenomenological expression for the photodiode response time that accounts for the displacement current effects is proposed and used to compare with the experimental results.
The photosensitivity linearity of a back-illuminated, pin photodiode arrays built on 75-&mgr;m thick single silicon dies is
discussed. Photosensitivity linearity measurements were performed in the range of input light fluxes above ~1nW/pixel
and the linearity was found to be better than 0.01% within the spectral range from 450 to 1000 nm. For lower light
fluxes, the non-linearity of the photo-sensitivity was smaller than the noise current of the array pixels and different
methods should be applied to measure the photosensitivity linearity with an accuracy of better than 0.1%. The theoretical
limits for the sensitivity linearity measurements are discussed. This work describes also the automatic probe system for
opto-electrical testing of the front- and backside illuminated photodiode arrays. The system allows 100% testing of
wafers and dies before die attach. The system is configured to work on wafers up to 150 mm in size or single multi-pixel
dies.
KEYWORDS: Back illuminated sensors, Resistance, PIN photodiodes, Temperature metrology, Diffusion, Photodiodes, Imaging systems, Silicon, Chemical elements, Medical imaging applications
Noise characteristics of the backlit, pin photodiode arrays having different vertical structures were studied. We showed that in many cases, the non-optical crosstalk between adjacent elements determines the noise performance and detectivity of the array pixels. For the arrays with the structure described in our recent works, the crosstalk always remained well below 0.01%, which allowed reaching the minimum noise level of ~ 10-15 A/&sqrt;Hz determined by the thermal noise. In contrast, for the arrays built applying conventional structures the crosstalk was two orders of magnitude higher, which noticeably decreased the sensitivity of the pixels increasing their noise and switching their operation towards background-limited performance. The background signal originated from the non-optical crosstalk and produced a noise level significantly higher that the thermal noise. We also compared the temperature coefficients for different arrays. For the structures with improved electrical crosstalk, the measured value of the shunt resistance temperature
coefficient was typically below 8 %/C and the responsivity temperature coefficient value did not exceed +0.02%/C within the spectral range from 450 through 800 nm. The advantages and drawbacks of application of the reported in this work photodiode arrays in high quality imaging systems are discussed.
Noise characteristics of the backlit, pin photodiode arrays having different vertical structures were studied. We showed that in many cases, the non-optical crosstalk between adjacent elements determines the noise performance and detectivity of the array pixels. For the arrays with the structure described in our recent works, the crosstalk always remained well below 0.01%, which allowed reaching the minimum noise level of ~ 10-15 A/&sqrt;Hz determined by the thermal noise. In contrast, for the arrays built applying conventional structures the crosstalk was two orders of magnitude higher, which noticeably decreased the sensitivity of the pixels increasing their noise and switching their operation towards background-limited performance. The background signal originated from the non-optical crosstalk and produced a noise level significantly higher that the thermal noise. We also compared the temperature coefficients for different arrays. For the structures with improved electrical crosstalk, the measured value of the shunt resistance temperature coefficient was typically below 8 %/C and the responsivity temperature coefficient value did not exceed +0.02 %/C within the spectral range from 450 through 800 nm. The advantages and drawbacks of application of the reported in this work photodiode arrays in high quality imaging systems are discussed.
Key features of a novel pin photodiode array structure built on 30-μm, 75-μm, and 100-μm thick single Silicon dies are discussed for the first time. Results of comparative studies of opto-electrical properties for a wide range of element sizes from ~ 200 μm square to ~ 1 mm square with the gaps between the adjacent elements as small as <20 μm are presented. The internal quantum efficiency was close to 100%, crosstalk was smaller than 0.01% within the spectral range 400 to 800 nm. The crosstalk remained lower than 0.1% even in the case when the illuminated element was electrically isolated (open contact). Furthermore very low leakage current and high shunt resistance (above 1 GΩ) are characteristic for these devices. The results are imperative for creating of high quality imaging systems.
Results of comparative studies of opto-electrical properties of photodiode arrays built on 30-um, 75-um, and 100-um thick single Silicon dies are presented. The size of the square pixels varied from 1.5 mm to 250-um for different arrays with the gaps between adjacent elements as small as 20 um. The internal quantum efficiency was close to 100%, DC and AC cross talks were smaller than 0.01% within the spectral range 400 to 800 nm. The arrays were characterized with very low leakage currents and high shunt resistance - above 1 GΩhm. The features of the array structure are discussed for the first time.
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