Comparison of the effects of 51-MeV protons on differing silicon avalanche photodiode structures

Different silicon avalanche photodiode structures are compared for the effects of 5 I -MeV protons on dark current and responsivity. Large differences in depletion widths coincided with differences in sensitivity to dark current increases and responsivity degradation. INTRODUCTION The ongoing interest in spacsbased light detection and ranging (LIDAR) experimentation continues to create a demand for highly sensitive and radiation tolerant photodetectors. Avalanche photodiodes (APDs) are often chosen for LIDAR systems due to their low noise and high gain compared to conventional detectors. For space applications requiring high sensitivity, radiation-induced changes in device parameters such as responsivity and dark current need to be quantified so that intensity dependent data are correctly interpreted. Limited radiation testing of APDs has been done previously [ 11, however radiation effects on differing avalanche photodiode structures have not been widely researched. This study examines two different silicon avalanche photodiode structures: a conventional APD from Advanced Photonix and an IR-enhanced APD from Perkin Elmer. Results for a third device type from Pacific Silicon will be included in the final paper. EXPERIMENTAL PROCEDURE characteristics: the RCA Type C30954E “reach through” structure by Perkin Elmer, and the 03670-62-53 1 by Advanced Photonix. Both are high speed APDs with active area diameters of 0.8 and 0.9 mm, respectively. However, there is an important dissimilarity. The reach through structure is enhanced for near infrared wavelengths, and has similar responsivity at 800nm and 1 micron. The Advanced Photonix APD has a more typical responsivity curve, for a silicon detector, which peaks at 800nm and falls off rapidly for longer wavelengths. The IR-enhanced APD has a much larger active collection depth because of the long absorption depth near the silicon bandgap edge. The APDs were irradiated at UC Davis using 5 1 -MeV protons. Samples of the Advanced Photonix device were irradiated with Cobalt-60 gamma rays in order to compare proton and gamma radiation effects. All devices were irradiated and evaluated under reverse bias. Pre-irradiation gain was approximately 100 for the Advanced Photonix device and 200 for the Perkin Elmer device. 800nm LED’s were the light source for responsivity measurements. 800nm is near the peak of the responsivity curves for these detectors and close to 8 15nm, a water absorption line that is important for certain LIDAR atmospheric studies. The IRenhanced structure was also evaluated at 1064nm, and that data will be presented in the final paper along with data on un-biased irradiations and annealing. Three samples of each device were tested at 800nm. Irradiations were conducted at room temperature, and preand postirradiation characterization was done at 22C. Two silicon APD structures were studied to determine how proton and gamma radiation affect their *The research in this paper was carried out at the Jet Propulsion Laboratory, Califomia Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA), under the NASA Electronic Parts and Packaging Program, Code AE.