Ralph W. Young

Ultralow power silicon microdisk modulators and switches

We demonstrate a 4 mum silicon microdisk modulator with a power consumption of 85 fJ/bit. The modulator utilizes a reverse-biased, vertical p-n junction to achieve 10 Gb/s data transmission with 3.5 V drive voltage, BER<10-12, and without signal pre-emphasis. High-speed silicon bandpass switches are constructed from pairs of modulators.

Vertical junction silicon microdisk modulators and switches

Vertical junction resonant microdisk modulators and switches have been demonstrated with exceptionally low power consumption, low-voltage operation, high-speed, and compact size. This paper reviews the progress of vertical junction microdisk modulators, provides detailed design data, and compares vertical junction performance to lateral junction performance. The use of a vertical junction maximizes the overlap of the depletion region with the optical mode thereby minimizing both the drive voltage and power consumption of a depletion-mode modulator. Further, the vertical junction enables contact to be made from the interior of the resonator and therein a hard outer wall to be formed that minimizes radiation in small diameter resonators, further reducing the capacitance and drive power of the modulator. Initial simple vertical junction modulators using depletion-mode operation demonstrated the first sub-100 fJ/bit silicon modulators. With more intricate doping schemes and through the use of AC-coupled drive signals, 3.5 μm diameter vertical junction microdisk modulators have recently achieved a communications efficiency of 3 fJ/bit, making these modulators the smallest and lowest power modulators demonstrated to date, in any material system. Additionally, the demonstration was performed at 12.5 Gb/s, required a peak-to-peak signal level of only 1 V, and achieved bit-error-rates below 10(-12) without requiring signal pre-emphasis. As an additional benefit to the use of interior contacts, higher-order active filters can be constructed from multiple vertical-junction modulators without interference of the electrodes. Doing so, we demonstrated second-order active high-speed bandpass switches with ~2.5 ns switching speeds, and power penalties of only 0.4 dB. Through the use of vertical junctions in resonant modulators, we have achieved the lowest power consumption, lowest voltage, and smallest silicon modulators demonstrated to date.

Low-Voltage, Compact, Depletion-Mode, Silicon Mach–Zehnder Modulator

Through rigorous process, electrical, and optical simulations, we develop a new silicon depletion-mode vertical p-n junction phase-modulator implemented in Mach-Zehnder modulator configuration, enabling an ultralow measured V ¿ L of only ~ 1 V·cm. Further, in a 500-¿m-long lumped element device, we demonstrate a 10-Gb/s nonreturn-to-zero data transmission with wide-open complementary output eye diagrams without the use of signal preemphasis.

Adiabatic Resonant Microrings (ARMs) with directly integrated thermal microphotonics

A new class of microphotonic-resonators, Adiabatic Resonant Microrings (ARMs), is introduced. The ARM resonator geometry enables heater elements to be formed within the resonator, simultaneously enabling record low-power (4.4 W/GHz) and record high-speed (1µs) thermal tuning.

Adiabatic thermo-optic Mach–Zehnder switch

In this Letter, we propose and demonstrate a high-speed and power-efficient thermo-optic switch using an adiabatic bend with a directly integrated silicon heater to minimize the heat capacity and therein maximize the performance of the thermo-optic switch. A rapid, τ=2.4 μs thermal time constant and a low electrical power consumption of P(π)=12.7 mW/π-phase shift were demonstrated representing a P(π)τ product of only 30.5 mW·μs in a compact device with a phase shifter of only ~10 μm long.

Enhancement-mode double-top-gated metal-oxide-semiconductor nanostructures with tunable lateral geometry

We present measurements of silicon (Si) metal-oxide-semiconductor (MOS) nanostructures that are fabricated using a process that facilitates essentially arbitrary gate geometries. Stable Coulomb-blockade behavior showing single-period conductance oscillations that are consistent with a lithographically defined quantum dot is exhibited in several MOS quantum dots with an open-lateral quantum-dot geometry. Decreases in mobility and increases in charge defect densities (i.e., interface traps and fixed-oxide charge) are measured for critical process steps, and we correlate low disorder behavior with a quantitative defect density. This work provides quantitative guidance that has not been previously established about defect densities and their role in gated Si quantum dots. These devices make use of a double-layer gate stack in which many regions, including the critical gate oxide, were fabricated in a fully qualified complementary metal-oxide semiconductor facility.

Charge sensing in enhancement mode double-top-gated metal-oxide-semiconductor quantum dots

Laterally coupled charge sensing of quantum dots is highly desirable because it enables measurement even when conduction through the quantum dot itself is suppressed. In this work, we demonstrate such charge sensing in a double-top-gated metal-oxide-semiconductor system. The current through a point contact constriction integrated near a quantum dot shows sharp 2% changes corresponding to charge transitions between the dot and a nearby lead. We extract the coupling capacitance between the charge sensor and the quantum dot, and we show that it agrees well with a three-dimensional capacitance model of the integrated sensor and quantum dot system.

Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry

We present transport measurements of a tunable silicon metal-oxide semiconductor double quantum dot device with lateral geometry. The experimentally extracted gate-to-dot capacitances show that the device is largely symmetric under the gate voltages applied. Intriguingly, these gate voltages themselves are not symmetric. A comparison with numerical simulations indicates that the applied gate voltages serve to offset an intrinsic asymmetry in the physical device. We also show a transition from a large single dot to two well isolated coupled dots, where the central gate of the device is used to controllably tune the interdot coupling.

Maximally confined silicon microphotonic modulators and switches

We demonstrate a 4 mum silicon microdisk modulator with a reverse-biased, vertical p-n junction. The modulator demonstrates a power consumption of 85 fJ/bit at a data rate of 10 Gb/s, 3.5 V drive, BER<10-12, and without signal pre-emphasis. High-speed silicon bandpass switches are constructed from pairs of modulators.

Quantum computer aided design simulation and optimization of semiconductor quantum dots

We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling multi-dimensional quantum devices, particularly silicon multi-quantum dots (QDs) developed for quantum bits (qubits). This finite-element simulator has three differentiating features: (i) its core contains nonlinear Poisson, effective mass Schrodinger, and Configuration Interaction solvers that have massively parallel capability for high simulation throughput and can be run individually or combined self-consistently for 1D/2D/3D quantum devices; (ii) the core solvers show superior convergence even at near-zero-Kelvin temperatures, which is critical for modeling quantum computing devices; and (iii) it interfaces directly with the full-featured optimization engine Dakota. In this work, we describe the capabilities and implementation of the QCAD simulation tool and show how it can be used to both analyze existing experimental QD devices through capacitance calculations and aid in the design of few-electron multi-QDs. In parti...