The avalanche buildup timet, which is related to the multiplication factor (M) byt=tgr;1M, where tgr;1is the intrinsic response time, is studied for silicon reachhyphen;through avalanche photodiodes (RAPDrsquo;s) by a shothyphen;noise measurement in the GHz region. The dependences ofton both the length of the avalanche regionlaand the wavelength exciting the avalanche process (lgr;) are investigated. The tgr;1values obtained increase withlain the regionlagsim;1.0 mgr;m and also take larger values for lgr;sim;6300 Aring; than for lgr;sim;8300 Aring;. These values are in good agreement with a calculation using the modified Emmons equation tgr;1=Nkeffla/vsexcept for the very narrow avalanche region (lalsim;0.4 mgr;m), whereNis a constant dependent onla,keffis the effective ratio of hole to electron ionization rates, andvsis the carrier saturation velocity. These results are very useful to investigate the frequency response of RAPDrsquo;s. The diodes discussed are used extensively in fiber transmission systems.
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