Noise in high speed avalanche photodiodes

摘要: We have measured the noise properties of high speed silicon and germanium avalanche photodiodes in frequency range from a few megacycles up to several Gc, for photocurrent multiplications including breakdown. At microwave frequencies, voltages less than breakdown, mean square current as function increasing multiplication M shows two distinct regions. For low values M, power is observed increase approximately 2.5 qualitative agreement with simple model fluctuations M. limited by time constant associated multiplication. Noise measurements this region yield value (typically 2-4\times10^{-12} sec) which reasonable obtained directly demodulation experiments. frequencies increases even more rapidly breakdown region, where decreases reciprocal current. An important practical implication these results that best signal-to-noise ratio achieved when such multiplied shot just equal sum series resistance receiver noise. Further multiplication, effect, only amplifies faster it does signal. Thus, although improve detector sensitivity, minimum detectable signal will still depend on