I zyxwvutsrqponmlkji IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 39, NO. zyxwvutsrqp 11. NOVEMBER 1992 zyxwvutsrq 2623 zyx 0.0 , 1 I I I I ! I I 0 10 20 30 40 zyxwvutsrqpon 50 60 70 Spatial Frequency -f- (cyc/mm) Fig. 2. Comparisons of MTF calculations using MTF = MTF, . MTF, (indicated by the dashed curves), and the unified model of this work (in- dicated by the discrete points). The expression for MTFD is from Seib [2], and MTF, = sin zyxwvutsrqponm (?rfa)/(?rfa). It should be noted that the MTF increases as the aperture decreases at a given spatial frequency and wavelength for both models. The basic parameters used for both models are zyxwvutsrqp p = 8 pm, yo = 3.5 pm, and zyxwvutsrqp Lo = 50 pm. IV. CONCLUSIONS A physically based, unified model to calculate the MTF of a solid-state imager including the effects of lateral diffusion of car- riers and sampling aperture has been presented. It has been found from this work that these effects cannot be treated independently and then later combined using the convolution theorem to amve at the total sensor MTF as is often done, except for the case where the pixel’s aperture is equal to its pitch. Although a simple aperture function and model for crosstalk were used in this work, others could be used. In any event, it has been shown that the sensor MTF must be calculated using a unified detector model that includes both of these effects (and possibly any or all of those mentioned in Sec- tion XI, or others if appropriate). It was found that as the crosstalk of the sensor increases for a given aperture size andlor as the sampling aperture is reduced with respect to the pixel size, the discrepancy between the MTF’s as calculated by (1) and the unified model presented in this work in- creases. This has implications for devices with small pixels and shallow depletion regions built on materials characterized by low absorption and long diffusion lengths. However, multiplying the diffusion and aperture MTF’s as indicated by (1) may be a reason- able, worst case approximation for situations where the pixel-to- pixel crosstalk is small, and/or the spatial frequencies of interest are low. ACKNOWLEDGMENT The author wishes to acknowledge many useful discussions with Dr. J. P. Lavine of Microelectronics Technology at Eastman Ko- dak Company. The author also wishes to acknowledge conversa- tions with M. J. Marchywka [12] at the Solar Physics Branch of the Naval Research Laboratory that led to this investigation. REFERENCES [ l ] M. H. Crowell and E. F. Labuda, “The silicon diode array camera tube,” Bell Syst. Tech. J., vol. 48, pp. 1481-1528, 1969. [2] D. H. Seib, “Camer diffusion degradation of modulation transfer function in charge coupled imagers, ” ZEEE Trans. Electron Devices, vol. ED-21, no. 3, pp. 210-217, 1974. [3] M. M. Blouke and D. A. Robinson, “A method for improving the spatial resolution of frontside-illuminated CCD’s,” ZEEE Trans. Electron Devices, vol. ED-28, no. 4, pp. 251-256, 1981. [4] J. P. Lavine, E. A. Trabka, B. C. Burkey, T. J. Tredwell, E. T. Nelson, and C. Anagnostopoulos, “Steady-state photocamer collec- tion in silicon imaging devices,” ZEEE Trans. Electron Devices, vol. ED-30, no. 9, pp. 1123-1134, 1983. (JPL has pointed out that the right-most divisor in their equation (1 1) has a sign error, and should read [l/L; - (Y + PI.) [5] D. Levy, S. E. Schacham, and 1. Kidron, “Three-dimensional ana- lytical simulation of self- and cross-responsivities of photovoltaic de- tector arrays,” ZEEE Trans. Electron Devices, vol. ED-34, no. 10, [6] J. P. Lavine, W.-C. Chang, C. N. Anagnostopoulos, B. C. Burkey, and E. T. Nelson, “Monte Carlo simulation of the photoelectron crosstalk in silicon imaging devices,” ZEEE Trans. Electron Devices, vol. ED-32, no. 10, pp. 2087-2091, 1985. [7] For example: D. F. Barbe, “Time delay and integration image sen- sors,” in Solid-Stare Imaging, P. G. Jespers, F. Van de Wiele, and M. H. White, Eds. Leyden, The Netherlands: Noordhoff, 1976, pp. 659-671. [8] N. Teranishi and Y. Ishihara, “Smear reduction in the interline CCD image sensor,’’ ZEEE Trans. Electron Devices, vol. ED-34, no. 5, [9] W. Buchtemann, “Modulatlon transfer function of extrinsic Si-detec- tor arrays affected by optical crosstalk,” ZEEE Trans. Electron De- vices, vol. ED-27, no. l, pp. 189-193, 1980. [lo] S. G. Chamberlain and D. H. Harper, “MTF simulation including transmittance effects and experimental results of charge-coupled im- agers,” ZEEE Trans. Electron Devices, vol. ED-25, no. 2, pp. 145- 154, 1978. [ 1I] In The Optical Industry and Systems Directory-Encyclopedia. Massachusetts: Optical Publishing, 1976, p. E-152. 1121 M. J. Marchywka and D. G. Socker, “An MTF measurement tech- nique for small pixel detectors,” to be published. pp. 2059-2070, 1987. pp. 1052-1056, 1987. Double Carrier Injection in the Sidegating Effect in GaAs MESFET’s Dima D. Shulman and Lawrence Young Abstract-Double injection into the semi-insulating substrate was in- vestigated as a mechanism of sidegating in GaAs MESFET’s. A change of gate current with sidegate voltage and a correlation between abrupt variations in drain, gate, and sidegate currents and instabilities in test devices support a physical model in which a gradual decrease of drain current with a nonlinear potential profile across the substrate is caused by low-level double injection and an abrupt decrease of drain current is caused by high-level double injection. I. INTRODUCTION AND MODEL Sidegating, an important parasitic effect with GaAs integrated circuits, is a decrease in the MESFET drain current on applying a negative potential to a nearby contact (sidegate). Lee et al. [l] ex- plained a correlation between substrate current and sidegating in Manuscript received June 8, 1991; revised June 8, 1992. This work was supported by the Natural Sciences and Engineering Research Council of Canada. The review of this brief was arranged by Associate Editor M. Shur. The authors are with the Department of Electrical Engineering, Univer- sity of British Columbia, Vancouver B. C., Canada V6T 124. IEEE Log Number 9202947. 0018-9383/92$03.00 zyxwvut 0 1992 IEEE 7