Jun-Fei Zheng

Ga2O3(Gd2O3)∕Si3N4 dual-layer gate dielectric for InGaAs enhancement mode metal-oxide-semiconductor field-effect transistor with channel inversion

A dual-layer gate dielectric approach for application in III-V metal-oxide-semiconductor field-effect transistor (MOSFET) was studied by using ultrahigh vacuum deposited 7–8nm thick Ga2O3(Gd2O3) as the initial dielectric to unpin the surface Fermi level of In0.18Ga0.82As and then molecular-atomic deposition of ∼2–3nm thick Si3N4 as a second dielectric protecting Ga2O3(Gd2O3). The total equivalent oxide thickness achieved in this study is 5nm. We have demonstrated an enhancement mode In0.18Ga0.82As∕GaAs MOSFET with surface inverted n channel with drain current (Id) of 0.1mA for a gate length of 10μm and a gate width of 880μm at Vds=1V and Vg=4.5V.

Multifunctional integrated photonic switches

Traditional optical-electronic-optical (o-e-o) conversion in todays optical networks requires cascading separately packaged electronic and optoelectronic chips and propagating high-speed electrical signals through and between these discrete modules. This increases the packaging and component costs, size, power consumption, and heat dissipation. As a remedy, we introduce a novel, chip-scale photonic switching architecture that operates by confining high-speed electrical signals in a compact optoelectronic chip and provides multiple network functions on such a single chip. This new technology features low optical and electrical power consumption, small installation space, high-speed operation, two-dimensional scalability, and remote electrical configurability. We present both theoretical and experimental discussion of our monolithically integrated photonic switches that incorporate quantum-well waveguide modulators directly driven by on-chip surface-illuminated photodetectors. These switches can be conveniently arrayed two-dimensionally on a single chip to realize a number of network functions. Of those, we have experimentally demonstrated arbitrary wavelength conversion across 45 nm and dual-wavelength broadcasting over 20 nm, both spanning the telecommunication center band (1530-1565 nm) at switching speeds up to 2.5 Gb/s. Our theoretical calculations predict the capability of achieving optical switching at rates in excess of 10 Gb/s using milliwatt-level optical and electrical switching powers.

Dual-diode quantum-well modulator for C-band wavelength conversion and broadcasting

We present a dual-diode, InGaAsP/InP quantum-well modulator that incorporates a monolithically-integrated, InGaAs photodiode as a part of its on-chip, InP optoelectronic circuit. We theoretically show that such a dual-diode modulator allows for wavelength conversion with 10-dB RF-extinction ratio using 7 mW absorbed optical power at 10 Gb/s. We experimentally demonstrate unlimited wavelength conversion across 45 nm between 1525 nm and 1570 nm, and dual-wavelength broadcasting over 20 nm between 1530 nm and 1565 nm, spanning the entire C-band with >10dB RF-extinction ratio and using 3.1-6.7 mW absorbed optical power at 1.25 Gb/s.

Optically controlled electroabsorption modulators for unconstrained wavelength conversion

We introduce a proof-of-concept, optically controlled, optical switch based on the monolithic integration of a surface-illuminated photodetector and a waveguide electroabsorption modulator. We demonstrate unconstrained wavelength conversion over the entire center telecommunication wavelength band (C band) and optical switching up to 2.5 Gbit/s with extinction ratios exceeding 10 dB. Our approach offers both high-speed, low-power, switching operation and two-dimensional array scalability for the fabrication of chip-scale reconfigurable multichannel wavelength converters.

Self-aligning planarization and passivation for integration applications in III-V semiconductor devices

This work reports an easy planarization and passivation approach for the integration of III-V semiconductor devices. Vertically etched III-V semiconductor devices typically require sidewall passivation to suppress leakage currents and planarization of the passivation material for metal interconnection and device integration. It is, however, challenging to planarize all devices at once. This technique offers wafer-scale passivation and planarization that is automatically leveled to the device top in the 1-3-/spl mu/m vicinity surrounding each device. In this method, a dielectric hard mask is used to define the device area. An undercut structure is intentionally created below the hard mask, which is retained during the subsequent polymer spinning and anisotropic polymer etch back. The spin-on polymer that fills in the undercut seals the sidewalls for all the devices across the wafer. After the polymer etch back, the dielectric mask is removed leaving the polymer surrounding each device level with its device top to atomic scale flatness. This integration method is robust and is insensitive to spin-on polymer thickness, polymer etch nonuniformity, and device height difference. It prevents the polymer under the hard mask from etch-induced damage and creates a polymer-free device surface for metallization upon removal of the dielectric mask. We applied this integration technique in fabricating an InP-based photonic switch that consists of a mesa photodiode and a quantum-well waveguide modulator using benzocyclobutene (BCB) polymer. We demonstrated functional integrated photonic switches with high process yield of >90%, high breakdown voltage of >25 V, and low ohmic contact resistance of /spl sim/10 /spl Omega/. To the best of our knowledge, such an integration of a surface-normal photodiode and a lumped electroabsorption modulator with the use of BCB is the first to be implemented on a single substrate.

Integrated photonic switches for nanosecond packet-switched optical wavelength conversion

We present a multifunctional photonic switch that monolithically integrates an InGaAsP/InP quantum well electroabsorption modulator and an InGaAs photodiode as a part of an on-chip, InP optoelectronic circuit. The optical multifunctionality of the switch offers many configurations to allow for different optical network functions on a single chip. Here we experimentally demonstrate GHz-range optical wavelength-converting switching with only ~10 mW of absorbed input optical power, electronically controlled packet switching with a reconfiguration time of <2.5 ns, and optically controlled packet switching in <300 ps.

Scalable wavelength-converting crossbar switches

We report scalable low-power wavelength-converting crossbar switches that monolithically integrate two-dimensional compact arrays of surface-normal photodiodes with quantum-well waveguide modulators. We demonstrate proof-of-concept, electrically reconfigurable 2/spl times/2 crossbars that perform unconstrained wavelength conversion across 35 nm in the C-band (1530-1565 nm), using only <4.3-mW absorbed input optical power, and with 10-dB extinction ratio at 1.25 Gb/s. Such wavelength-converting crossbars provide complete flexibility to selectively convert any of the input wavelengths to any of the output wavelengths at high data bit rates in telecommunication, with the input and output wavelengths being arbitrarily chosen within the C-band.

Intimate monolithic integration of chip-scale photonic circuits

In this paper, we introduce a robust monolithic integration technique for fabricating photonic integrated circuits comprising optoelectronic devices (e.g., surface-illuminated photodetectors, waveguide quantum-well modulators, etc.) that are made of completely separate epitaxial structures and possibly reside at different locations across the wafer as necessary. Our technique is based on the combination of multiple crystal growth steps, judicious placement of epitaxial etch-stop layers, a carefully designed etch sequence, and self-planarization and passivation steps to compactly integrate optoelectronic devices. This multigrowth integration technique is broadly applicable to most III-V materials and can be exploited to fabricate sophisticated, highly integrated, multifunctional photonic integrated circuits on a single substrate. As a successful demonstration of this technique, we describe integrated photonic switches that consume only a 300 /spl times/300 /spl mu/m footprint and incorporate InGaAs photodetector mesas and InGaAsP/InP quantum-well modulator waveguides separated by 50 /spl mu/m on an InP substrate. These switches perform electrically-reconfigurable optically-controlled wavelength conversion at multi-Gb/s data rates over the entire center telecommunication wavelength band.

Optically-switched dual-diode electroabsorption modulator

We introduce the monolithic integration of a waveguide electroabsorption modulator with a surface-normal photodiode for the realization of a novel, low-power, optically-controlled optical switch. We demonstrate a selective-area regrowth technique that meets the integration requirements.

Novel optically-controlled optical switch based on intimate integration of surface-normal photodiode and waveguide electroabsorption modulator for wavelength conversion

For optical-electronic-optical (o-e-o) conversion without the use of conventional electronics, we introduce a novel, highly-integrated, chip-scale, optically-controlled optical switch that incorporates a surface-normal photodiode (PD) and a waveguide electroabsorption modulator (EAM) on the same substrate. Such an integrated optical switch avoids the difficulties and the limitations of ordinary o-e-o conversion, and eliminates the need for separate packaging of its individual parts.