Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Peer reviewedPostprin

Two-dimensional III-VIA semiconductors and their applications in optoelectronic devices

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 04-12-202

STUDY OF CMOS COMPATIBLE RUTHENIUM OXIDE SCHOTTKY CONTACTS FOR ALGAN/GAN AND INALN/GAN DIODES AND HIGH MOBILITY TRANSISTORS GROWN ON SILICON (111) SUBSTRATES

Ph.DDOCTOR OF PHILOSOPH

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

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

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

Charge storage and transport in metal oxide resistive switching devices

Metal oxide resistive switching devices are designed and prepared using atomic layer deposition (ALD) and spin coating methods. The electrical and optical characteristics are studied for their applications in memory, photo-detection, and chemical sensing. Two electrically dissimilar ZnO thin film layers produced by using two different ALD recipes on a Si substrate as a bilayer is studied and found to have characteristics (rectification, hysteresis, and threshold voltage) needed to solve the crosstalk problem in crossbar memory array. ZnO bilayer device has fingerprint of a memristive device with AC frequency. The ratio of high to low resistive states (HRS/LRS) increases, reaches its maximum and starts to decrease with increasing frequency of applied AC voltage which is attributed to the diffusion dominating low frequency transport and charge freeze at high frequency. The maximum HRS/LRS achieved at 1 kHz is 2.3. Next part of the study deals with the α-Fe₂O₃ thin films on p-Si and glass substrates. α-Fe₂O₃ /p-Si samples show excellent ultra-fast visible light photo-detection property of response times under 10 µs with large zero bias photocurrent of >16 nA. The study of resistive switching properties of the α-Fe₂O₃ /p-Si samples reveals that it has synaptic potentiation property of neurons. The device's conductance increases with increasing voltage pulse applied to it and saturates at its maximum after some pulses. The mathematical hill function fit to the conductance data shows that activation of the device is programmable with the intensity of white light illumination. α-Fe₂O₃ /glass sample shows the coexistence of resistive switching and negative differential resistance phenomena in the presence of humid air with the transport analysis, it is attributed to the formation of the space charge at the material electrode interface. The same sample is used to quantify the relative humidity in air by using a novel sweeping I-V method