Abstract
This paper reviews materials and structural approaches that have been developed to reduce the excess noise in avalanche photodiodes and increase the gain-bandwidth product.
Highlights
For applications that are not background limited, the most common sources of noise in an optical receiver are dark current, noise of the amplifier that follows the detector, or the quantum noise in the signal
The fact that Si has an indirect bandgap and, relatively low absorption coefficient constrains the bandwidth of Si detectors. Owing to their low dark current, high detection efficiency, and low noise, Si avalanche photodiode (APD) remain the detectors of choice for applications in the visible that do not require high speed
The noise is quantified by an excess noise factor, F(M), in the range 1.1 and 1.4.24,25 The low noise appears to result from novel aspects of the bandstructure; the effective mass ratio is very large and unlike most III-V semiconductors, Hg0.7Cd0.3Te has a very small valley band gap (0.25 eV), and very high satellite L and X valleys (1.5 eV and 2.5 eV, respectively).[26]
Summary
For applications that are not background limited, the most common sources of noise in an optical receiver are dark current, noise of the amplifier that follows the detector, or the quantum noise in the signal. The ionization coefficient ratio k = is a key factor for the multiplication noise and bandwidth of an APD. For k = 1, since the process is somewhat chain-like, if an impact event does not occur, the variation in to total gain is much greater than for the k=0 case Later is was found that the excess noise factor could be significantly reduced by scaling the multiplication region to exploit the non-local aspect of impact ionization. With only a couple of exceptions, the APDs described in this paper employ mesa structures
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