Photodetectors based on novel materials and structures for fiber optical communications and long wavelength sensing.

摘要

Photonic devices, with particular emphasis on photodetecotors, have been studied based on novel materials and device structures for applications in fiber optical communication systems and long wavelength sensing. Two types of novel materials, Tl- and N-containing compounds, are investigated for applications in detectors with response in the near- and mid-infrared wavelength region. While the attempt to grow InTlP and InGaTlAs alloys on InP substrates results in no significant incorporation of Tl due to the fundament chemical properties of Tl, we have successfully grown lattice-matched InGaAsN alloys with high structural quality on InP substrates by gas source molecular beam epitaxy (GSMBE), with an extended bandgap cutoff wavelength of up to 2.02 μm (∼0.6 eV).; Two types of devices, InGaAs(P)N/InP long wavelength p-i-n detectors and long wavelength InGaAsN/GaAs quantum well (QW) lasers, have been fabricated based upon the high crystalline quality of the nitride alloys. An InGaAsN/InP photodetector is demonstrated with a cutoff wavelength up to 2.1μm. High performance InGaAsN/GaAs QW lasers with threshold current densities of 1.15 kA/cm2 and 1.85 kA/cm2, internal quantum efficiencies of 82% and 52%, are also demonstrated at emission wavelength of λ = 1.3 and 1.4 μm, respectively.; Compared with p-i-n detectors, avalanche photodiodes (APDs) are attractive for deployment in fiber optical communication links due to the improved sensitivities at high bit rates (>2.5 Gb/s). Two novel APD structures have been studied. First, by employing a double diffused floating guard ring (FGR) structure to eliminate edge breakdown, we demonstrate InGaAs/InP separate absorption-and-multiplication region avalanche photodiodes (SAM-APDs) for applications in low-cost, high bandwidth (≤10 Gb/s) optical communication links. The device shows a gain of 7 without edge breakdown for a multiplied dark current of ∼5 nA, and a gain-bandwidth product ≥60 GHz. To realize 40 Gb/s operation, an asymmetric twin-waveguide (ATG) structure has been applied to an InGaAs/InP/InAlAs SAM-APD. The device has an external quantum efficiency of (48 ± 1.5)% at λ = 1.55 μm, a 3dB bandwidth of (28.5 ± 0.5) GHz with gain of up to 4, suitable for 40 Gb/s, NRZ format, optical communication systems.