Integrated GHz silicon photonic interconnect with micrometer-scale modulators and detectors

We report an optical link on silicon using micrometer-scale ring-resonator enhanced silicon modulators and waveguide-integrated germanium photodetectors. We show 3 Gbps operation of the link with 0.5 V modulator voltage swing and 1.0 V detector bias. The total energy consumption for such a link is estimated to be ~120 fJ/bit. Such compact and low power monolithic link is an essential step towards large-scale on-chip optical interconnects for future microprocessors

Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

Two-dimensional materials offer new opportunities for both fundamental science and technological applications, by exploiting the electron spin. While graphene is very promising for spin communication due to its extraordinary electron mobility, the lack of a band gap restricts its prospects for semiconducting spin devices such as spin diodes and bipolar spin transistors. The recent emergence of 2D semiconductors could help overcome this basic challenge. In this letter we report the first important step towards making 2D semiconductor spin devices. We have fabricated a spin valve based on ultra-thin (5 nm) semiconducting black phosphorus (bP), and established fundamental spin properties of this spin channel material which supports all electrical spin injection, transport, precession and detection up to room temperature (RT). Inserting a few layers of boron nitride between the ferromagnetic electrodes and bP alleviates the notorious conductivity mismatch problem and allows efficient electrical spin injection into an n-type bP. In the non-local spin valve geometry we measure Hanle spin precession and observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 um. Our experimental results are in a very good agreement with first-principles calculations and demonstrate that Elliott-Yafet spin relaxation mechanism is dominant. We also demonstrate that spin transport in ultra-thin bP depends strongly on the charge carrier concentration, and can be manipulated by the electric field effect

Development of suspended thermoreflectance technique and its application in thermal property measurement of semiconductor materials

Doctor of PhilosophyDepartment of Mechanical and Nuclear EngineeringGurpreet SinghThis dissertation details the development of a new scientific tool for the thermal characterization of freestanding micro/nano-scale materials, with specific application to thin films. The tool consists of a custom-designed and calibrated opto-electric system with superior spatial and temporal resolutions in thermal measurement. The tool, termed as Suspended ThermoReflectance (STR), can successfully perform thermal mappings at the submicron level and is able to produce unconstrained thermal conductivity unlike other optical measurement techniques where independent conductivity measurement is not possible due to their reliance on heat capacity. STR works by changing the temperature of a material and collecting the associated change in light reflection from multiple points on the sample surface. The reflection is a function of the material being tested, the wavelength of the probe light and the composition of the specimen for transparent and quasi-transparent materials. Coupling the change in reflection, along the sample’s length, with the knowledge of heat conduction allows for the determination of the thermal properties of interest. A thermal analytical model is developed and incorporated with optical equations to characterize the conductivity of thin films. The analytical model is compared with a finite element model to check its applicability in the STR experiment and data analysis. Ultimately, thermal conductivity of 2 µm and 3 µm thick Si samples were determined using STR at a temperature range of 20K – 350K and compared to literature as a validation of the technique. The system was automated using a novel LabView-based program. This program allowed the user to control the equipment including electronics, optics and optical cryostat. Moreover, data acquisition and real-time monitoring of the system are also accomplished through this computer application. A description of the development, fabrication and characterization of the freestanding thin films is detailed in this dissertation. For the most part, the thin films were fabricated using standard microfabrication techniques. However, different dry and wet etching techniques were compared for minimum surface roughness to reduce light scattering. The best etching technique was used to trim the Si films for the desired thicknesses. Besides, vapor HF was used to avoid stiction-failure during the release of suspended films

Low-background temperature sensors fabricated on parylene substrates

Temperature sensors fabricated from ultra-low radioactivity materials have been developed for low-background experiments searching for neutrinoless double-beta decay and the interactions of WIMP dark matter. The sensors consist of electrical traces photolithographically-patterned onto substrates of vapor-deposited parylene. They are demonstrated to function as expected, to do so reliably and robustly, and to be highly radio-pure. This work is a proof-of-concept study of a technology that can be applied to broad class of electronic circuits used in low-background experiments

Micropattern gas detector technologies and applications, the work of the RD51 collaboration

The RD51 collaboration was founded in April 2008 to coordinate and facilitate efforts for development of micropattern gaseous detectors (MPGDs). The 75 institutes from 25 countries bundle their effort, experience and resources to develop these emerging micropattern technologies. MPGDs are already employed in several nuclear and high-energy physics experiments, medical imaging instruments and photodetection applications; many more applications are foreseen. They outperform traditional wire chambers in terms of rate capability, time and position resolution, granularity, stability and radiation hardness. RD51 supports efforts to make MPGDs also suitable for large areas, increase cost-efficiency, develop portable detectors and improve ease-of-use. The collaboration is organized in working groups which develop detectors with new geometries, study and simulate their properties, and design optimized electronics. Among the common supported projects are creation of test infrastructure such as beam test and irradiation facilities, and the production workshop.Comment: Submitted to the IEEE Nuclear Science Symposium 2010 Conference Recor

Development of type II superlattice infrared detectors monolithically integrated on silicon substrates

The project’s objective is the development of an InAs/GaSb type II superlattice (T2SL) medium wavelength infrared photodiode directly grown on Si substrate for the use of an infrared single pixel photodiode. The T2SL has been selected as the replacement for the state-of-the-art CdHgTe (CMT). The use of Si substrate will help with the integration into the Si-based technology by reducing the fabrication process and costs. The T2SL is a photon detector with overlapping multiple quantum well structure and a type 2 bandgap alignment. The T2SL are fabricated using a combination of materials from the group III-V in order to achieve a well-controlled ultra-thin heterostructures using molecular beam epitaxy as a growth technique. The structure within the active region is designed to enhance the performance of the T2SL architecture by manipulating the thickness and doping of each layer. The direct growth of a T2SL structure on the Si substrate has achieved similar structural and optical properties when compared to that grown on the GaAs substrate. The Si architecture has an absorption edge of 5.365μm when measured at 70K: dark current density at -1V is 4x101A/cm2; responsivity (R) peak is 1.2A/W; quantum efficiency (QE) at -0.1V is 32.5%; and specific detectivity (D*) peak is 1x109cmHz½/W. The pπBn has best architecture over GaAs substrate due to the wide bandgap unipolar barrier. The pπBn has an absorption edge of 6.5 μm when measured at 77K: dark current density under -0.6V is 5x10-3A/cm2; R peak is 0.6A/W; QE at 0V and 3.25μm is 23%; and D* peak is 1x1011cmHz½/W. These results demonstrate that the D* of the pπBn structure is just one order of magnitude smaller than the state-of-the-art CMT detector which is 2x1012cmHz1/2W