151 research outputs found
Thermal conductivity and photoluminescence of light-emitting silicon nitride films
Silicon-rich and rare-earth-doped nitride materials are promising candidates for silicon-compatible photonic sources. This work investigates the thermal conductivity and photoluminescence (PL) of light emitting samples fabricated with a range of excess silicon concentrations and annealing temperatures using time-domain picosecond thermoreflectance and time-resolved photoluminescence. A direct correlation between the thermal conductivity and photoluminescence dynamics is demonstrated, as well as a significant reduction of thermal conductivity upon incorporation of erbium ions. These findings highlight the role of annealing and stoichiometry control in the optimization of light emitting microstructures suitable for the demonstration of efficient Si-compatible light sources based on the silicon nitride platform. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3682508
Thermoreflectance techniques and Raman thermometry for thermal property characterization of nanostructures
This AIP article is published under license by AIP: https://publishing.aip.org/wp-content/uploads/2019/10/AIPP-Author-License.pdfPublishing.https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlAltres ajuts: ICN2 is supported by the CERCA Programme/Generalitat de Catalunya.The widespread use of nanostructures and nanomaterials has opened up a whole new realm of challenges in thermal management, but also leads to possibilities for energy conversion, storage, and generation, in addition to numerous other technological applications. At the microscale and below, standard thermal measurement techniques reach their limits, and several novel methods have been developed to overcome these limitations. Among the most recent, contactless photothermal methods have been widely used and have proved their advantages in terms of versatility, temporal and spatial resolution, and even sensitivity in some situations. Among them, thermoreflectance and Raman thermometry have been used to measure the thermal properties from bulk materials to thin films, multilayers, suspended structures, and nanomaterials. This Tutorial presents the principles of these two techniques and some of their most common implementations. It expands to more advanced systems for spatial mapping and for probing of non-Fourier thermal transport. Finally, this paper concludes with discussing the limitations and perspectives of these techniques and future directions in nanoscale thermometry
Ultrafast evanescent heat transfer across solid interfaces via hyperbolic phonon polaritons in hexagonal boron nitride
The efficiency of phonon-mediated heat transport is limited by the intrinsic
atomistic properties of materials, seemingly providing an upper limit to heat
transfer in materials and across their interfaces. The typical speeds of
conductive transport, which are inherently limited by the chemical bonds and
atomic masses, dictate how quickly heat will move in solids. Given that
phonon-polaritons, or coupled phonon-photon modes, can propagate at speeds
approaching 1 percent of the speed of light - orders of magnitude faster than
transport within a pure diffusive phonon conductor - we demonstrate that
volume-confined, hyperbolic phonon-polariton(HPhP) modes supported by many
biaxial polar crystals can couple energy across solid-solid interfaces at an
order of magnitude higher rates than phonon-phonon conduction alone. Using
pump-probe thermoreflectance with a mid-infrared, tunable, probe pulse with
sub-picosecond resolution, we demonstrate remote and spectrally selective
excitation of the HPhP modes in hexagonal boron nitride in response to
radiative heating from a thermally emitting gold source. Our work demonstrates
a new avenue for interfacial heat transfer based on broadband radiative
coupling from a hot spot in a gold film to hBN HPhPs, independent of the broad
spectral mismatch between the pump(visible) and probe(mid-IR) pulses employed.
This methodology can be used to bypass the intrinsically limiting phonon-phonon
conductive pathway, thus providing an alternative means of heat transfer across
interfaces. Further, our time-resolved measurements of the temperature changes
of the HPhP modes in hBN show that through polaritonic coupling, a material can
transfer heat across and away from an interface at rates orders of magnitude
faster than diffusive phonon speeds intrinsic to the material, thus
demonstrating a pronounced thermal transport enhancement in hBN via
phonon-polariton coupling
Ultrafast laser pulses to detect and generate fast thermo-mechanical transients in matter
The use of femtosecond laser pulses to impulsively excite thermal and mechanical transients in matter has led, in the last years, to the development of picosecond acoustics. Recently, the pump-probe approach has been applied to nanoengineered materials to optically generate and detect acoustic waves in the gigahertz terahertz frequency range. In this paper, we review the latest advances on ultrafast generation and detection of thermal gradients and pseudo-surface acoustic waves in 2-D lattices of metallic nanostructures. Comparing the experimental findings to the numeric analysis of the full thermomechanical problem, these materials emerge as model systems to investigate both the mechanical and thermal energy transfer at the nanoscale. The sensitivity of the technique to the nanostructure mass and shape variations, coupled with the phononic crystal properties of the lattices, opens the way to a variety of applications ranging from hypersonic waveguiding to mass sensors with femtosecond time resolution
Diffraction Model of Thermoreflectance Data
Diffraction based mathematical model is developed to address the issue of spatial resolution in thermoreflectance imaging at the scale of 1 and 10 μm. Thermoreflectance imaging provided non-contact temperature measurement at micro and nano scale but the spatial resolution is limited by diffraction. By virtue of this work mathematical model is developed for the analysis of thermoreflectance data. In the development of model both the diffraction occurring at sample and substrate is combined to calculate intensity of thermoreflectance signal. This model takes into account the effective optical distance, sample width, wavelength, signal phase shift and reflectance intensity. Model shows qualitative and quantitative agreement with experimental data for the two wavelengths under investigation, 470 nm and 535 nm
Accurate temperature measurements on semiconductor devices.
Self-heating can have a detrimental effect on the performance and reliability of high power microwave devices. In this work, the thermal performance of the gallium arsenide (GaAs) Gunn diode was studied. Infrared (IR) thermal microscopy was used to measure the peak operating temperature of the graded-gap structured device. Temperature measurements were experimentally validated using micro-thermocouple probing and compared to values obtained from a standard 1D thermal resistance model. Thermal analysis of the conventionally structured Gunn diode was also undertaken using high resolution micro-Raman temperature profiling, IR thermal microscopy and electro/thermal finite element modeling.
The accuracy of conventional IR temperature measurements, made on semiconductor devices, was investigated in detail. Significant temperature errors were shown to occur in IR temperature measurements made on IR transparent semiconductors layers and low emissivity/highly reflective metals. A new technique, employing spherical carbon microparticles, was developed to improve the measurement accuracy on such surfaces. The new ‘IR microparticle’ technique can be used with existing IR microscopes and potentially removes the need to coat a device with a high emissivity layer, which causes damage and heat spreading
High Resolution Thermal Imaging for Electrical and Optical Characterization of Electronic and Photonic Devices.
The impact of heating on electronic and optoelectronic devices is becoming increasingly severe as devices scale to smaller and smaller sizes. High temperature not only reduces most performance metrics, but also decreases device lifetime. In order to study and understand these problems, an important step is to measure temperature at small size scales.
Here we show how CCD-based thermoreflectance temperature measurement can be successfully applied to heterojunction bipolar transistors, quantum well lasers, and quantum dot lasers for device thermal characterization with a spatial resolution of 400 nm and a temperature resolution of 10 mK. Indeed, the high spatial resolution of this technique allows one to resolve separate heat sources within a device itself; rather than viewing the entire device as a monolithic heat source, we are able to study the separate internal heat transport mechanisms that often exist.
Specifically, in applying CCD-based thermoreflectance to SiGe-based heterojunction bipolar transistors, we show how temperature mapping can be used to spatially profile device current, including asymmetric behavior such as current hogging. In examining a type of high-power laser, we show how (with proper light filtering) 2D temperature profiles of the facet can be measured and linked to thermal lensing. We then describe how the CCD-based thermoreflectance setup can be modified to accommodate pulsed devices, demonstrating the technique on pulsed InGaAs quantum dot lasers and identifying separate temperature peaks due to active region heating and contact heating.
Finally, we discuss how the measurement of thermal and thermoelectric properties in organic thin films can be used to derive fundamental and device-relevant electrical properties related to interface transport. By measuring the Seebeck coefficient of an OTFT, we show that one can for the first time successfully evaluate the channel thickness in a non-destructive fashion without further fabrication processes.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/57661/2/klchan_1.pd
Thermomechanical issues of high power laser diode catastrophic optical damage
Catastrophic optical damage (COD) of high power laser diodes is a crucial factor limiting
ultra high power lasers. The understanding of the COD process is essential to improve the
endurance of the high power laser diodes. COD is observed as a process in which the active
part of the laser diode is destroyed, forming characteristic defects, the so called dark line
defects (DLDs). The DLDs are formed by arrays of dislocations generated during the laser
operation. Local heating associated with non-radiative recombination is assumed to be at the
origin of the COD process. A summary of the methods used to assess the COD, both in real
time and post-mortem is presented. The main approaches developed in recent years to model
the heat transport in the laser structures under non homogeneous temperature distribution are
overviewed. Special emphasis is paid to the impact of the low dimensionality of QWs in two
physical properties playing a major role in the COD process, namely, thermal conductivity
and mechanical strength. A discussion about the impact of the nanoscale in both physical
properties is presented. Finally, we summarize the main issues of the thermomechanical
modelling of COD. Within this model the COD is launched when the local thermal stresses
generated around the heat source overcome the yield stress of the active zone of the laser. The
thermal runaway is related to the sharp decrease of the thermal conductivity once the onset of
plasticity has been reached in the active zone of the laser.Junta de Castilla y León (Projects VA081U16 and VA283P18)Spanish Government (ENE 2014-56069-C4-4-R, ENE 2017-89561-C4-3-R, FPU programme 14/00916)
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