Extending device performance in photonic devices using piezoelectric properties

This study focuses on the influence of epi-layer strain and piezoelectric effects in asymmetric GaInAs/GaAlAs action regions that potentially lead to intra-cavity frequency mixing. The theoretical limits for conduction and valence band offsets in lattice-matched semiconductor structures have resulted in the deployment of non-traditional approaches such as strain compensation to extend wavelength in intersubband devices, where strain limits are related to misfit dislocation generation. Strain and piezoelectric effects have been studied and verified using select photonic device designs. Metrics under this effort also included dipole strength, oscillator strength, and offset of energy transitions, which are strongly correlated with induced piezoelectric effects. Unique photonic designs were simulated, modeled, and then fabricated using solid-source molecular beam epitaxy into photonic devices. The initial designs produce lambda wavelength, and the introduction of the piezoelectric effect resulted in lambda/2 wavelength. More importantly, this work demonstrates that the theoretical cutoff wavelength in intersubband lasers can be overcome

Orientation-dependent pseudomorphic growth of InAs for use in lattice-mismatched mid-infrared photonic structures

In this study, InAs was deposited on GaAs (100) and GaAs (111)B 2 degrees towardssubstrates for the purpose of differentiating the InAs growth mode stemming from strain and then analyzed using in-situ reflection high energy electron diffraction, scanning electron microscopy, Raman spectroscopy, reflectance spectroscopy, and atomic force microscopy. The procession of InAs deposition throughout a range of deposition conditions results in assorted forms of strain relief revealing that, despite lattice mismatch for InAs on GaAs (approximately 7%), InAs does not necessarily result in typical quantum dot/wire formation on (111) surfaces, but instead proceeds two-dimensionally due primarily to the surface orientation

Spectroscopy studies of straincompensated mid-infrared QCL active regions on misoriented substrates

In this work, we perform spectroscopic studies of AlGaAs/InGaAs quantum cascade laser structures that demonstrate frequency mixing using strain-compensated active regions. Using a three-quantum well design based on diagonal transitions, we incorporate strain in the active region using single and double well configurations on various surface planes (100) and (111). We observe the influence of piezoelectric properties in molecular beam epitaxy grown structures, where the addition of indium in the GaAs matrix increases the band bending in between injector regions and demonstrates a strong dependence on process conditions that include sample preparation, deposition rates, mole fraction, and enhanced surface diffusion lengths. We produced mid-infrared structures under identical deposition conditions that differentiate the role of indium(strain) in intracavity frequency mixing and show evidence that this design can potentially be implemented using other material systems

Pseudomorphic growth of InAs on misoriented GaAs for extending quantum cascade laser wavelength

The authors have studied the impact of epilayer strain on the deposition of InAs/GaAs on (100) and (111)B with 2 degrees offset toward 2-1-1 surfaces. Consequences of a 7% lattice mismatch between these orientations in the form of three-dimensional growth are less apparent for (111)B with 2 degrees offset toward 2-1-1 surfaces compared to (100). By exploring a range of molecular beam epitaxy process parameters for InAs/GaAs growth and utilizing scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to evaluate the quality of these strained layers, the authors develop empirical models that describe the influence of the process conditions in regards to surface roughness with \u3e92% accuracy. The smoothest InAs/GaAs samples demonstrated average surface roughness of 0.08 nm for 10 um-squre areas, albeit at very low deposition rates. The authors have found the most important process conditions to be substrate temperature and deposition rate, leading us to believe that controlling diffusion length may be the key to reducing defects in severely strained structures. InGaAs/AlGaAs quantum cascade laser structures were also produced on (111)B with 2 degrees offset toward 2-1-1 to take advantage of the piezoelectric effect, and the modified laser transitions due to these effects were observed

Charge storage characteristics of ultra-small Pt nanoparticle embedded GaAs based non-volatile memory

Charge storage characteristics of ultra-small Pt nanoparticle embedded devices were characterized by capacitance-voltage measurements. A unique tilt target sputtering configuration was employed to produce highly homogenous nanoparticle arrays. Pt nanoparticle devices with sizes ranging from ∼0.7 to 1.34 nm and particle densities of ∼3.3–5.9 × 1012 cm−2 were embedded between atomic layer deposited and e-beam evaporated tunneling and blocking Al2O3 layers. These GaAs-based non-volatile memory devices demonstrate maximum memory windows equivalent to 6.5 V. Retention characteristics show that over 80% charged electrons were retained after 105 s, which is promising for device applications

Reduced auger recombination in mid-infrared semiconductor lasers

A quantum-design approach to reduce the Auger losses in two micron InGaSb type-I quantum well edge-emitting lasers is reported. Experimentally realized structures show a 3X reduction in the threshold, which results in 4.6 lower Auger current loss at room temperature. This is equivalent to a carrier lifetime improvement of 5.7 and represents about a 19-fold reduction in the equivalent “Auger coefficient.

Nonlinear and dynamic modeling of stainless steel strands using artificial neural networks [abstract]

Abstract only availableIn this study, artificial neural networks (ANNs) are used to model a collection of acoustic signals that propagate down a stainless steel strand embedded in concrete. The study of acoustic signals in stainless steel strands is important because steel strands are used to strengthen concrete structures such as bridges, walkways, overpasses, buildings, etc. Unfortunately, stainless steel strands are susceptible to corrosion, which can be the source of various catastrophic failures. The acoustic signals are launched, using Electromagnetic Acoustic Transducers (EMATs), in a stainless steel strand that has been mechanically altered to simulate the corrosion process and to monitor the corrosion that has taken place. The information in the acoustic signals has proven to be extremely difficult to evaluate. Therefore, using principal component analysis (a data compression technique) the large dataset, consisting of over 10,000 points, is compressed down to three principle components (PCs). After the appropriate file conversions have taken place, the PCs are fed into an ANN in order to predict the amount of corrosion within the stainless steel strand. The acoustic signals are compressed, modeled, and predicted with up to 91% accuracy. The neural network structure was optimized to allow 10000:3 data compression ration of acoustic signal intensity values to PCs.McNair Scholars Progra

Process modeling of InAs/AISb materials for high electron mobility transisitors grown by molecular beam epitaxy

Ph.D.Directed by Gary S. Ma

Development of optical models for non-invasive glucose testing [abstract]

Abstract only availableCurrent blood glucose measurement techniques are invasive and uncomfortable. Developing a non-invasive technique will not only alleviate part of the pain involved with current techniques but also cost less, greatly benefiting over 16 million diabetics in America. The technical road block impeding current progress is the development of a technique to obtain the current glucose levels through the skin. This is extremely complex due to the inhomogeneous nature of skin and various elements that absorb large spectrums that overlap with the absorption spectrum of glucose. A model accounting for the inhomogeneous nature and absorption spectrum within the skin could help to determine the ideal characteristics of low energy radiation that penetrate the skin and obtain valuable information beneath the dermis layer. In this work, we begin the development of optical models for investigating the feasibility of this non-invasive approach.College of Engineering Undergraduate Research Optio

An optical model for non-invasive measurements of human blood glucose level [abstract]

Faculty Mentor: Dr. Gregory Triplett, Electrical and Computer EngineeringAbstract only availableNumerous technical challenges preventing the development of non-invasive blood measurement techniques involve the interfaces between the primary skin layers. The ability to accurately and non-invasively measure human glucose level characteristics potentially lies within optical-based systems. Current reliable blood analysis techniques invariably require intravenous blood extraction. A much preferred blood flow measurement setup would utilizes harmless levels of electromagnetic radiation that penetrates beneath the skin and provides feedback which corresponds with important properties of red blood cells, the hemoglobin and hence glucose levels. However, there exist numerous major technical challenges, which include the lack of accurate models that describe light interaction and characteristics of the skin, particularly at the interface between the primary layers: the epidermis, and dermis. It remains essential to explore alternative approaches that may evolve into reliable, accurate, and pain-free blood analysis techniques that account for the interactions between these critical skin layers. The development of a physical model of the skin will provide a framework for exploring integrated optoelectronic systems. In this work, the optical response of the skin layers is explored