Why small avalanche photodiodes are beautiful

Conventional wisdom suggests that, for low avalanche noise, avalanche photodiodes should operate at low electric fields, where electron and hole ionisation coefficients can differ widely. However, the associated weak ionisation requires long multiplication regions, which in turn demand high bias voltages and result in long carrier transit times, reducing device speed. Moreover, multiplication is particularly sensitive to temperature in this region. In this paper we discuss the effects of dead space on reducing noise in short devices and on the associated benefits in predicted response time and reduced temperature sensitivity. The paper is illustrated with work from the Sheffield group.