A reexamination of silicon avalanche photodiode gain and quantum efficiency

Traditionally the measured gain of an avalanche photodiode (APD) has been considered the product of two parameters: the multiplication process and quantum efficiency (QE), the former being wavelength dependent and the latter being bias independent. We propose a new examination of these related parameters where the APD gain is considered intrinsic, defined as being the amount of electron multiplication each photoelectron undergoes based on the applied bias, and independent of the incident photon wavelength, and the QE being considered intrinsic as a function of only wavelength and bias. This is a more logical, and physically real, perspective of APD behavior. We introduce a technique to measure the intrinsic gain and the intrinsic QE of a deep diffused silicon APD. The mechanisms by which the gain and QE vary as a function of wavelength involve charge collection and light absorption due to the light penetration depth dependency on wavelength. Once the intrinsic gain vs. bias of the APD is measured, it becomes possible to use this measurement as an absolute parameter. With the intrinsic gain known, we show how the intrinsic QE of an APD, for a given wavelength, changes as a function of bias. We also show that when the APD is operated from the low to high gain regime, light at 400 nm to 800 nm experiences an increase in QE, while light at longer wavelengths experiences a reduction in QE. These fundamental, dynamic and operational properties of APDs are critical when considering the wavelength(s) that are of interest for a given application