High-speed quantum-dot resonant-cavity SACM avalanche photodiodes operating at 1.06 /spl mu/m

Abstract

The two most commonly used avalanche photodiodes (APDs) for near infrared applications are Si reach-through APDs or InGaAs/InP APDs with separate absorption and multiplication (SAM) regions. However, the wavelength region near 1 /spl mu/m is near the long-wavelength cutoff for Si photodiodes and the short-wavelength end of the spectral response of InGaAs-InP photodiodes. The best commercially available Si-IR enhanced APDs demonstrate quantum efficiencies below 40% and bandwidths below 250 MHz, while InGaAs/InP-based APDs shows higher dark current and higher avalanche noise. The wavelength of Nd:YAG lasers, 1.06 um, falls in this sensitivity valley. Recently, it has been shown that self-assembled quantum-dots (QDs) can be utilized to extend the operating wavelength of GaAs-based materials to much longer wavelengths than can be accomplished with quantum wells. In the paper we describe a resonant-cavity separate absorption, charge and multiplication (SACM) In/sub 0.5/Ga/sub 0.5/As APD structure. Compared to our previous work, the gain has been increased from /spl sim/18 to >50 and we have measured the frequency response. In the low gain regime, the bandwidth is 35 GHz and at higher gains, where the frequency response is determined by the gain-bandwidth product, we observe a gain-bandwidth product of 220 GHz. To put this result in context, the best multiple-quantum-well APDs that are used for fiber optic transmission systems have gain-bandwidth products of 150 GHz.