Robert L. Jarecki

Control of coherent information via on-chip photonic–phononic emitter–receivers

Rapid progress in integrated photonics has fostered numerous chip-scale sensing, computing and signal processing technologies. However, many crucial filtering and signal delay operations are difficult to perform with all-optical devices. Unlike photons propagating at luminal speeds, GHz-acoustic phonons moving at slower velocities allow information to be stored, filtered and delayed over comparatively smaller length-scales with remarkable fidelity. Hence, controllable and efficient coupling between coherent photons and phonons enables new signal processing technologies that greatly enhance the performance and potential impact of integrated photonics. Here we demonstrate a mechanism for coherent information processing based on travelling-wave photon–phonon transduction, which achieves a phonon emit-and-receive process between distinct nanophotonic waveguides. Using this device, physics—which supports GHz frequencies—we create wavelength-insensitive radiofrequency photonic filters with frequency selectivity, narrow-linewidth and high power-handling in silicon. More generally, this emit-receive concept is the impetus for enabling new signal processing schemes.

Ultrasmooth microfabricated mirrors for quantum information

In this paper, we realize a scalable micromirror suitable for atom chip based cavity quantum electrodynamics applications. A very low surface roughness of 2.2 A rms on the silicon cavity mirrors is achieved using chemical dry etching along with plasma and oxidation smoothing. Our Fabry–Perot cavity comprised of these mirrors currently demonstrates the highest finesse, F=64 000, using microfabricated mirrors. We compute a single atom cooperativity for our cavities of more than 200, making them promising candidates for detecting individual atoms and for quantum information applications on a chip.

Ge–Si separate absorption and multiplication avalanche photodiode for Geiger mode single photon detection

A Ge–Si separate absorption and multiplication avalanche photodiode (SAM-APD) is reported. The structure is grown using a low temperature in situ clean and epitaxy process, Tinsitu and Tepitaxy<∼460°C, resulting in a Ge layer with a dislocation density of ∼5×1010cm−2. The SAM-APD has a responsivity of 3.2×10−4A∕W (1310nm) and a dark current density at punch-through of 0.2mA∕cm2. In Geiger mode (GM) at 206K, the dark count rates (DCRs) are ∼280kHz, which is within an order of magnitude of DCR reported for InGaAs∕InP GM APDs despite the high defect density in the Ge.

Infrared rectification in a nanoantenna-coupled metal-oxide-semiconductor tunnel diode

Direct rectification of electromagnetic radiation is a well-established method for wireless power conversion in the microwave region of the spectrum, for which conversion efficiencies in excess of 84% have been demonstrated. Scaling to the infrared or optical part of the spectrum requires ultrafast rectification that can only be obtained by direct tunnelling. Many research groups have looked to plasmonics to overcome antenna-scaling limits and to increase the confinement. Recently, surface plasmons on heavily doped Si surfaces were investigated as a way of extending surface-mode confinement to the thermal infrared region. Here we combine a nanostructured metallic surface with a heavily doped Si infrared-reflective ground plane designed to confine infrared radiation in an active electronic direct-conversion device. The interplay of strong infrared photon-phonon coupling and electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast electronic tunnelling in metal-oxide-semiconductor (MOS) structures. Infrared dispersion of SiO2 near a longitudinal optical (LO) phonon mode gives large transverse-field confinement in a nanometre-scale oxide-tunnel gap as the wavelength-dependent permittivity changes from 1 to 0, which leads to enhanced electromagnetic fields at material interfaces and a rectified displacement current that provides a direct conversion of infrared radiation into electric current. The spectral and electrical signatures of the nanoantenna-coupled tunnel diodes are examined under broadband blackbody and quantum-cascade laser (QCL) illumination. In the region near the LO phonon resonance, we obtained a measured photoresponsivity of 2.7 mA W(-1) cm(-2) at -0.1 V.

Prediction of release-etch times for surface-micromachined structures

A one-dimensional model is presented which describes the release-etch behavior of sacrificial oxides in aqueous HF. Starting from first principles and an empirical rate law, release etch kinetics are derived for primitive geometries. The behavior of complex three-dimensional structures is described by joining the solutions of constituent primitives and applying appropriate boundary conditions. The two fitting parameters, k/sub 1/ and k/sub 2/, are determined from the simplest structure and describe the more complex structures well. Experimental validation of the model is presented with data for all of the geometries and four types of sacrificial oxides.

Release-etch modeling for complex surface-micromachined structures

A release etch model for etching sacrificial oxides in aqueous HF solutions is presented. This model is an extension of work done by Monk et. al. and Liu et. al The model is inherently one dimensional, but can be used to model the etching of complex three dimensional parts. Solutions and boundary conditions are presented for a number of geometries.

Superconductive Silicon Nanowires Using Gallium Beam Lithography

This work was an early career LDRD investigating the idea of using a focused ion beam (FIB) to implant Ga into silicon to create embedded nanowires and/or fully suspended nanowires. The embedded Ga nanowires demonstrated electrical resistivity of 5 m-cm, conductivity down to 4 K, and acts as an Ohmic silicon contact. The suspended nanowires achieved dimensions down to 20 nm x 30 nm x 10 m with large sensitivity to pressure. These structures then performed well as Pirani gauges. Sputtered niobium was also developed in this research for use as a superconductive coating on the nanowire. Oxidation characteristics of Nb were detailed and a technique to place the Nb under tensile stress resulted in the Nb resisting bulk atmospheric oxidation for up to years.

Silicon nanowire pirani sensor fabricated using FIB lithography

As radio frequency microelectromechanical systems (RF-MEMS) mature as a manufacturable technology, packaging of the devices becomes increasingly important. Devices such as aluminum nitride (AlN) RF-filters require packaging which is either hermetic or under vacuum to protect the devices [1]. It then becomes critical to have a measurement of pressure inside the packaged chamber. Typically for this need, Pirani gauges are fabricated using poly silicon or metal patterned on suspended membranes [2]. These type of devices increase die area, add complexity to fabrication flows, and difficulty when attempting to suspend the membranes. In this work we fabricate and characterize a suspended silicon nanowire for use as Pirani gauge by utilizing Ga lithography and plasma reactive ion etching for defining the nanowire geometry and simultaneously releasing the wire. This method benefits from the high surface to volume ratio inherent in the nano regime, decreased thermal conductivity of amorphous silicon (from implantation) and increased electrical conductivity of Ga doping to reduce device area and fabrication complexity of a Pirani gauge.

Fiber-optic polymer residue monitor

Semiconductor processing tools that use a plasma to etch polysilicon or oxides produce residue polymers that build up on the exposed surfaces of the processing chamber. These residues are generally stressed and with time can cause flaking onto wafers resulting in yield loss. Currently, residue buildup is not monitored, and chambers are cleaned at regular intervals resulting in excess downtime for the tool. In addition, knowledge of the residue buildup rate and index of refraction is useful in determining the state of health of the chamber process. We have developed a novel optical fiber-based robust sensor that allows measurement of the residue polymer buildup while not affecting the plasma process.

Substrate removal for ultra efficient silicon heater-modulators

We present our experimental results of ultra efficient (up to 2.16 nm/mW) thermally tunable modulators with n-type heaters and the Si substrate removed. To our knowledge, this is the most efficient thermally tunable modulator demonstrated at 1550nm to date. We include results of externally heated modulators with commensurate performance enhancements through substrate removal.