Abstract

Inherent in conventional separate absorption, grading and multiplication (SAGM) InP-based avalanche photodiode (APD) structures is a constraint between the doping level and length of the multiplication region.^1-3 The thinner the multiplication region, the higher the doping level and the achievable gain-bandwidth product (GBW) of the device. Unfortunately, as the multiplication region becomes thinner, the device fabrication tolerances become very stringent, requiring p-diffusion junction depth control of ±200 Å for a doping level of 6 × 10¹⁶ (Ref. 1). Even if the device can be fabricated, beyond a certain doping level [2 × 10¹⁷ cm⁻³ (Ref. 2)], the leakage current from tunneling in the InP multiplication region places a fundamental upper limit on the achievable GBW, which has been recently estimated to be 140 GHz.2 The highest GBW in an InP-based SAGM APD reported to date is 90 GHz,1 and Imai and Kaneda have commented that a GBW of 100 Gllz is unlikely to be achieved with a SAGM APD.³

© 1991 Optical Society of America