Abstract

A high saturation current InGaAs photodiode with a partially depleted absorber (PDA) is demonstrated. Less than 0.5 dB compression is observed in a 6-µm diameter photodiode at 20mA and 45GHz. The measured responsivity is 0.6 A/W. Recent developments in photodetecters for optical receivers have been focused on the potential for wide-bandwidth and high-output voltage operation. In an effort to increase the output pho-tocurrent (RF power), various surface-illuminated [1-5] and waveguide [6,7] structures have been investigated. The ability to increase the photocur-rent is limited by RF-response compression [8] and ultimately by thermal failure [9,10]. Compression is characterized by three different measurements: small-signal [1,2], pulsed (low duty cycle) [7,8], and large-signal [2,5,6] techniques. The small-signal compression current, used here, is defined [2] as the average DC photocurrent at which the RF response decreases by 1 dB for small modulation depth conditions. Surface-illuminated p-i-n structures, such as the uni-traveling-carrier (UTC) photodiode [1,3], the dual-depletion region (DDR) photodetecter [4], and traditional InP/InGaAs photodiodes [1,2], have achieved high photocurrent-bandwidth products. Williams and Esman [2] reported a compression current of 30mA at 20 GHz for mesa-geometry, n-side illuminated InP/InGaAs photodiodes. Of the various UTC structures, Fukano et al. [5] report a facet-coupled 47 GHz UTC with a responsivity of 0.8 A/W and a saturation current of 10mA. Waveguide photodetecters [6] also have achieved high-speed (50GHz), high saturation current (10mA), and high optical response (0.6A/W), but at the expense of a more complex device structure and edge coupling

© 2003 Optical Society of America