5,146 research outputs found
Extended Infrared Photoresponse in Te-Hyperdoped Si at Room Temperature
Presently, silicon photonics requires photodetectors that are sensitive in a
broad infrared range, can operate at room temperature, and are suitable for
integration with the existing Si-technology process. Here, we demonstrate
strong room-temperature sub-band-gap photoresponse of photodiodes based on Si
hyperdoped with tellurium. The epitaxially recrystallized Te-hyperdoped Si
layers are developed by ion implantation combined with pulsed-laser melting and
incorporate Te-dopant concentrations several orders of magnitude above the
solid solubility limit. With increasing Te concentration, the Te-hyperdoped
layer changes from insulating to quasi-metallic behavior with a finite
conductivity as the temperature tends to zero. The optical absorptance is found
to increase monotonically with increasing Te concentration and extends well
into the mid-infrared range. Temperature-dependent optoelectronic photoresponse
unambiguously demonstrates that the extended infrared photoresponsivity from
Te-hyperdoped Si p-n photodiodes is mediated by a Te intermediate band within
the upper half of the Si band gap. This work contributes to pave the way toward
establishing a Si-based broadband infrared photonic system operating at room
temperature.Comment: 18 pages, 7 figure
Progress towards on-chip single photon sources based on colloidal quantum dots in silicon nitride devices
New results on integration of colloidal quantum dots (QDs) into SiN microstructures are reported, including QD positioning with nanometric accuracy and the efficient coupling of their emission to waveguides and cavities. The results are relevant to on-chip quantum optics and information processing
Optical properties of refractory metal based thin films
There is a growing interest in refractory metal thin films for a range of emerging nanophotonic applications including high temperature plasmonic structures and infrared superconducting single photon detectors. We present a detailed comparison of optical properties for key representative materials in this class (NbN, NbTiN, TiN and MoSi) with texture varying from crystalline to amorphous. NbN, NbTiN and MoSi have been grown in an ultra-high vacuum sputter deposition system. Two different techniques (sputtering and atomic layer deposition) have been employed to deposit TiN. We have carried out variable angle ellipsometric measurements of optical properties from ultraviolet to mid infrared wavelengths. We compare with high resolution transmission electron microscopy analysis of microstructure. Sputter deposited TiN and MoSi have shown the highest optical absorption in the infrared wavelengths relative to NbN, NbTiN or ALD deposited TiN. We have also modelled the performance of a semi-infinite metal air interface as a plasmonic structure with the above mentioned refractory metal based thin films as the plasmonic components. This study has implications in the design of next generation superconducting nanowire single photon detector or plasmonic nanostructure based devices
Engineering chromium related single photon emitters in single crystal diamond
Color centers in diamond as single photon emitters, are leading candidates
for future quantum devices due to their room temperature operation and
photostability. The recently discovered chromium related centers are
particularly attractive since they possess narrow bandwidth emission and a very
short lifetime. In this paper we investigate the fabrication methodologies to
engineer these centers in monolithic diamond. We show that the emitters can be
successfully fabricated by ion implantation of chromium in conjunction with
oxygen or sulfur. Furthermore, our results indicate that the background
nitrogen concentration is an important parameter, which governs the probability
of success to generate these centers.Comment: 14 pages, 5 figure
Correlating Microstructure and Optoelectronic Performance of Carbon-Based Nanomaterials
There is a great deal of interest in carbon nanostructures such as graphene and various forms of carbon nanotubes due to their exceptional physical, electronic, and optical properties. Many technological applications have been proposed for these nanostructures, but despite the promise many carbon nanostructure-based optoelectronic devices fail to compete with their conventional counterparts. This is often due in large part to a non-optimized material or device microstructure. Factors such as crystallinity, contact quality, defect structure, and device configuration can critically affect device performance due to the high sensitivity and extreme surface to volume ratio of carbon nanostructures. In order for the exceptional intrinsic properties of the nanostructures to be exploited, a clear understanding of the microstructure and its correlation with device-relevant optoelectronic properties is needed. This dissertation presents four projects which demonstrate this principle. First, a TiO2-coated carbon nanofiber is studied in order to optimize its structure for use in a novel dye-sensitized solar cell. Second, the electrode configuration of an individual multiwall carbon nanotube infrared sensor is investigated in order to surpass the limitations of disordered nanotube film-based infrared sensors. Third, the properties of defect structures in large area transferred graphene films grown by chemical vapor deposition are correlated with carrier diffusion in order to understand the film's low mobility compared to exfoliated graphene. Fourth, the effect of deposition conditions on graphene-metal contact was studied with the goal of achieving sufficiently transparent contacts for investigation of the superconducting proximity effect. All four projects highlight the unique properties of carbon nanostructures as well as the need to correlate their optoelectronic properties with microstructural details in order to achieve the desired device performance
Deterministic integration of quantum dots into on-chip multi-mode interference beamsplitters using in-situ electron beam lithography
The development of multi-node quantum optical circuits has attracted great
attention in recent years. In particular, interfacing quantum-light sources,
gates and detectors on a single chip is highly desirable for the realization of
large networks. In this context, fabrication techniques that enable the
deterministic integration of pre-selected quantum-light emitters into
nanophotonic elements play a key role when moving forward to circuits
containing multiple emitters. Here, we present the deterministic integration of
an InAs quantum dot into a 50/50 multi-mode interference beamsplitter via
in-situ electron beam lithography. We demonstrate the combined emitter-gate
interface functionality by measuring triggered single-photon emission on-chip
with . Due to its high patterning resolution as well
as spectral and spatial control, in-situ electron beam lithography allows for
integration of pre-selected quantum emitters into complex photonic systems.
Being a scalable single-step approach, it paves the way towards multi-node,
fully integrated quantum photonic chips.Comment: 20 pages, 5 figure
Surface texturing of CVD diamond assisted by ultrashort laser pulses
Diamond is a wide bandgap semiconductor with excellent physical properties which allow it to operate under extreme conditions. However, the technological use of diamond was mostly conceived for the fabrication of ultraviolet, ionizing radiation and nuclear detectors, of electron emitters, and of power electronic devices. The use of nanosecond pulse excimer lasers enabled the microstructuring of diamond surfaces, and refined techniques such as controlled ablation through graphitization and etching by two-photon surface excitation are being exploited for the nanostructuring of diamond. On the other hand, ultrashort pulse lasers paved the way for a more accurate diamond microstructuring, due to reduced thermal effects, as well as an effective surface nanostructuring, based on the formation of periodic structures at the nanoscale. It resulted in drastic modifications of the optical and electronic properties of diamond, of which âblack diamondâ films are an example for future high-temperature solar cells as well as for advanced optoelectronic platforms. Although experiments on diamond nanostructuring started almost 20 years ago, real applications are only today under implementation
A Radiation Imaging Detector Made by Postprocessing a Standard CMOS Chip
An unpackaged microchip is used as the sensing element in a miniaturized gaseous proportional chamber. Thisletter reports on the fabrication and performance of a complete radiation imaging detector based on this principle. Our fabrication schemes are based on wafer-scale and chip-scale postprocessing.\ud
Compared to hybrid-assembled gaseous detectors, our microsystem shows superior alignment precision and energy resolution, and offers the capability to unambiguously reconstruct 3-D radiation tracks on the spot.\u
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