Jian Wei

An asymmetric twin-waveguide high-bandwidth photodiode using a lateral taper coupler

We describe a high-bandwidth high-responsivity low-polarization sensitivity p-i-n photodiode based on an integratable asymmetric twin-waveguide structure. Incident light is collected by a diluted large-fiber guide followed by transfer to a thin-coupling waveguide using a low-loss lateral-taper coupler. The light is finally absorbed by the uppermost In/sub 0.53/Ga/sub 0.47/As layer. The device has a responsivity of (0.75/spl plusmn/0.03) ampere per watt and a polarization sensitivity of /spl les/0.4 dB. The measured electrical 3 dB bandwidth is /spl ges/40 GHz. The responsivity is comparable with the best 40-GHz waveguide p-type-intrinsic-n-type photodiodes, while the twin-waveguide design provides a single-epitaxial growth step and a simple means of fabrication with possibility for monolithic integration of the photodiodes with other optical components, such as semiconductor optical amplifiers and in-plane waveguide filters.

Growth and characterization of small band gap (∼0.6 eV) InGaAsN layers on InP

We demonstrate the growth of small band gap (Eg∼0.6 eV) strained and lattice matched single crystal InGaAsN alloys on InP substrates. InGaAsN layers with N concentrations varying from 0.6% to 3.25% were grown by gas source molecular beam epitaxy using a radio frequency plasma nitrogen source. Lattice-matched, 0.5-μm-thick InGaAsN layers with smooth surface morphologies and abrupt interfaces were achieved. Low temperature photoluminescence measurements reveal a band gap emission wavelength of 1.9 μm (at 20 K) for lattice matched InGaAsN (N∼2%). Tensile strained In0.53Ga0.47As/In0.53Ga0.47As0.994N0.006 multiple quantum wells emitting at 1.75 μm at 20 K are also reported.

Low-threshold current, high-efficiency 1.3-μm wavelength aluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at /spl lambda/=1.3 /spl mu/m at a threshold current density of only J/sub TH/=1.32 kA/cm/sup 2/. These narrow ridge (W=8.5 /spl mu/m) lasers also exhibit an internal loss of only 3.1 cm/sup -1/ and an internal efficiency of 60%. Also, a characteristic temperature of T/sub 0/=150 K from 10/spl deg/C to 60/spl deg/C was measured, representing a significant improvement over conventional /spl lambda/=1.3 /spl mu/m InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125/spl deg/C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved.

Monolithic integration of a semiconductor optical amplifier and a high bandwidth p-i-n photodiode using asymmetric twin-waveguide technology

An optical mode transformer, a semiconductor optical amplifier (SOA), and a high-bandwidth waveguide-coupled photodiode are monolithically integrated using separately optimized materials based on asymmetric twin-waveguide (ATG) technology. Incident light is collected by a diluted, large fiber guide followed by transfer to an SOA. After amplification, light is coupled into the uppermost In/sub 0.53/Ga/sub 0.47/As light absorption layer by two consecutive taper couplers. The device shows a peak responsivity of 11 A/W (/spl sim/12.5-dB SOA-to-detector gain) and a 3-dB electrical bandwidth of 36 GHz, corresponding to a gain-bandwidth product of 640 GHz. In this SOA/p-i-n chip, separation of optical functions (light guiding, amplification, and detection) into different waveguides allows for optimization of materials for each function without material regrowth. Generalized photonic integrated circuits containing complex combinations of these three optical functions can be realized using the integration scheme demonstrated here.

A high-responsivity high-bandwidth asymmetric twin-waveguide coupled InGaAs-InP-InAlAs avalanche photodiode

The authors demonstrate an integratable high-responsivity high-bandwidth long wavelength InGaAs-InP-InAlAs avalanche photodiode based on an asymmetric twin-waveguide structure. The device has an external quantum efficiency of 48 /spl plusmn/ 1.5% at /spl lambda/ = 1.55 /spl mu/m, a 3-dB bandwidth of 28.5 /spl plusmn/ 0.5 GHz with gain of up to 4, and a fiber-to-waveguide misalignment tolerance of /spl plusmn/ 1.0 /spl mu/m in the vertical and /spl plusmn/ 1.3 /spl mu/m in the horizontal directions resulting in a 1-dB sensitivity penalty.

High T/sub 0/ long-wavelength InGaAsN quantum-well lasers grown by GSMBE using a solid arsenic source

We demonstrate high performance, /spl lambda/=1.3- and 1.4-/spl mu/m wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm/sup 2/ at /spl lambda/=1.3 and 1.4 /spl mu/m, respectively, were obtained for the lasers with a 7-/spl mu/m ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for /spl lambda/=1.3 and 1.4 /spl mu/m emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at /spl lambda/=1.3 /spl mu/m due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T/sub 0/=122 K and 100 K at /spl lambda/=1.3 and 1.4 /spl mu/m, respectively, as well as a low emission wavelength temperature dependence of (0.39/spl plusmn/0.01) nm//spl deg/C over a temperature range of from 10/spl deg/C to 60/spl deg/C.

High-performance long-wavelength (/spl lambda//spl sim/1.3 μm) InGaAsPN quantum-well lasers

We demonstrate high-performance InGaAsPN quantum well based long-wavelength lasers grown on GaAs substrates, nitrogen containing lasers emitting in the /spl lambda/=1.2- to 1.3-/spl mu/m wavelength range were grown by gas source molecular beam epitaxy using a RF plasma nitrogen source. Under pulsed excitation, lasers emitting at /spl lambda/=1.295 /spl mu/m exhibited a record low threshold current density (J/sub TH/) of 2. 5 kA/cm/sup 2/. Lasers grown with less nitrogen in the quantum well exhibited significantly lower threshold current densities of J/sub TH/=1.9 kA/cm/sup 2/ at /spl lambda/=1.27 /spl mu/m and J/sub TH/=1.27 kA/cm/sup 2/ at /spl lambda/=1.2 /spl mu/m. We also report a slope efficiency of 0.4 W/A and an output power of 450 mW under pulsed operation for nitrogen containing lasers emitting at 1.2 /spl mu/m.

Gas source molecular beam epitaxy grown InGaAs(P)N-InP long-wavelength (/spl lambda/>1.65 μm) photodetectors using a solid arsenic source

We demonstrate InGaAs(P)N-InP-based long-wavelength (/spl lambda/>1.65 /spl mu/m) p-i-n photodetectors grown lattice-matched to InP substrates using a solid As source. The background doping level in the absorption layer is significantly reduced from (5.0/spl plusmn/0.3)/spl times/10/sup 17/ cm/sup -3/ for gas source As grown devices to (3.5/spl plusmn/0.5)/spl times/10/sup 16/ cm/sup -3/ for solid source As grown devices with the same cutoff wavelength of 1.85 /spl mu/m. The external quantum efficiency at a wavelength of 1.56 /spl mu/m is 30% for the solid source grown detector as compared with 16% for the gas source grown detector due to the higher background doping and hence smaller depletion region width in the latter diode. Nitrogen-hydrogen complex formation and local strain-induced defects may significantly contribute to high free carrier concentrations observed in gas source As grown InGaAs(P)N layers.

InGaAsPN-InP-based photodetectors for long wavelength (/spl lambda/>1.65 μm) applications

We demonstrate InGaAsPN p-i-n photodetectors lattice-matched to InP substrates with cutoff wavelengths larger than 1.65 /spl mu/m. The narrow bandgap InGaAsPN absorption layers were grown by gas source molecular beam epitaxy using an RF plasma nitrogen source. Optical absorption spectra reveal that InGaAsPN with 5% P and 2.8% N has a cutoff wavelength /spl lambda//sub CO/=1.90 /spl mu/m Background doping in the absorption layer for a detector with 1.5% N and 5% P is reduced from (1.5/spl plusmn/0.5)/spl times/10/sup 17/ cm/sup -3/ for the as-grown device, to (5/spl plusmn/0.5)/spl times/10/sup 16/ cm/sup -3/ for a thermally annealed device. The unintentional high background doping is due to N-H bond formation or local strain induced defects. Spectral response measurements indicate that /spl lambda//sub CO/=1.85 /spl mu/m is achieved for detectors annealed at 800/spl deg/C with 2% N and 5% P in the InGaAsPN absorption layer, suggesting that annealed InGaAsPN alloys are promising for use in detectors with response in the near and mid-IR wavelength spectral range.

Optimization of double diffused floating guarding ring InGaAs/InP avalanche photodiodes

In this study, the double diffused FGR structure of a high-speed InGaAs/InP APD was optimized from both theoretical analysis and experimental results. A high-speed edge-breakdown-free APD with gain of more than 10 was demonstrated following the design rule. Noise of this APD was measured and analyzed incorporating the dead-space effect.