Advanced receiver technology for commercial threat warning systems
Advanced threat warning technology will begin to play a more significant role for Homeland defense and National security. Of particular concern are landing and take-off patterns of slow moving commercial airliners here and abroad. Recognizing this vulnerability has triggered renewed interest in high sensitivity internal gain optical detectors and 2D arrays. Avalanche photo detectors (APD’s) are the most highly sought after low-noise, high-gain photo sensors. They are being developed for highly sensitive LADAR receiver systems in autonomous munitions and for data communications (for example) and will be the “eyes” of modern commercial threat warning systems. This paper reviews several LADAR technologies and the corresponding requirements placed on APD’s. Performance of commercial and experimental APD’s will be discussed. Recent results on large format InAlAs APD arrays fabricated by the authors will also be presented.
Monte Carlo simulations of the bandwidth of InAlAs avalanche photodiodes
We present a Monte Carlo simulation of the bandwidth of an InAlAs avalanche photodiode with an undepleted absorber. The carrier velocities are simulated in the charge layer and the multiplication region. It is shown that the velocity overshoot effect is not as significant as simpler models have suggested. At high electric field intensity, the electron effective saturation velocity is only slightly higher when impact ionization is significant, compared with when impact ionization is absent. The simulated 3 dB bandwidth is consistent with experiments for gains up to 50.
PROOF COPY 034222APL Comparing leakage currents and dark count rates in Geiger-mode avalanche photodiodes
~Received 9 January 2002; accepted for publication 9 April 2002!This letter presents an experimental study of dark count rates and leakage current in Geiger-modeavalanche photodiodes ~GM APD!. Experimental results from circular diodes over a range of areas~20–500 mm diam!, exhibit leakage current levels orders of magnitude higher than anticipated fromdark count rates. Measurements of the area and peripheral components of the leakage currentindicate that the majority of the current in reverse bias does not enter the high-ﬁeld region of thediode, and therefore, does not contribute to the dark count rate. Extraction of the area leakagecurrent term from large-area devices~500 mm! corresponds well with the measured dark count rateson smaller devices ~20 mm!. Finally, the work indicates how dark count measurements represent10