University at Albany, State University of New York
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Al(x)In(y)Ga(1−x−y)N-based Monolithically Integrated IR Detector-Visible Emitter Device
Get PDFIII-Nitride material system has been widely used in electronic, sensing, optoelectronic, and power device applications. Owing to the wide and tunable bandgap of this material system and the realization of relatively high conductivity p-type Mg-doped GaN films, considerable research over the past few decades has focused on applications based on wide bandgaps, such as blue and ultraviolet (UV) light-emitting diodes (LEDs), laser diodes, visible-blind and solar-blind photodetectors. The other side of the spectrum, infrared (IR) has remained considerably less explored.
To exploit III-Nitrides for IR detection applications, the quantum well infrared photodetector (QWIP) design is employed. In the QWIP design, an artificially small bandgap region using wide bandgap materials is created. In this type of detector, a wide bandgap material (e.g., GaN or GaAs) is surrounded by a larger bandgap material (e.g., AlxGa1−xN or AlxGa1−xAs) to create a quantum well (QW) where transitions happen between confined (bound) energy states in the QWs in the conduction or the valence band, also known as intersubband transitions or ISBTs. The III-Nitride system is particularly well-suited for QWIP type structures/devices due to the large conduction and valence band offsets in Al(Ga)N/GaN heterostructures, allowing for a broad range of spectral detection. The system’s strong polarization offers additional design flexibility, permitting further tuning of band offset and therefore, of ISBT energies.
One of the challenges impeding the use of III-nitride-based QWIPs in imaging applications is the need for wavelength up-conversion to permit emission in the visible range. Without integrated up-conversion, the QWIP must have an additional readout circuit, which increases device complexity, size, and weight, making it undesirable for many handheld device applications. This challenge was overcome for IR detection-IR emission in GaAs/AlGaAs by monolithic integration of a QWIP and a multi quantum well (MQW) emitter. This thesis discusses an AlxInyGa1−x−yN-based monolithically integrated IR detector-Visible emitter device grown by metal organic chemical vapor deposition (MOCVD). For detection, a Mg-doped p-QWIP is utilized, which allows normal incident absorption based on quantum mechanics polarization selection rule.
A realistic device design and energy band diagram simulation for an integrated AlxGa1−xN/GaN QWIP with an InGaN/GaN MQW emitter for IR detection and emission in the visible range was developed and further optimized throughout the device development process. The integrated device’s layer thicknesses, dopings, and compositions were selected and developed based on feedback provided from material growth and characterization, device fabrication, and electrical characterization.
Targeting 1.55 μm absorption peak, energy band diagram simulations were developed and the valence band offset energy between GaN (QW) and different Al compositions (x) of AlxGa1−xN barrier layers was calculated. As a result, x = 0.45 (in AlxGa1−xN) barrier was selected, which creates ~0.8 eV valence band offset (for a target 1.55 μm absorption peak). MOCVD material growth space was developed to achieve nm-thick layers with high control over the growth rate, abrupt interfaces, and smooth surface morphology. Extensive material characterizations such as atomic force microscopy (AFM), X-ray diffraction (XRD), and scanning transmission electron microscopy (STEM) were used which demonstrated development of smooth and uniform surface morphology with low root-mean-square (RMS) roughness (\u3c 0.5 nm), high crystalline quality, and abrupt interfaces. QWIP devices were fabricated to measure the dark current density and photoresponsivity on a range of devices with varying mesa sizes, from ~100 μm to ~600 μm in diameter. I-V measurements revealed low dark current density in the range of ~10−4 to 10−6 A/cm2 on these photodetectors. Photoresponsivity with a broadband light source in the 700–2200 nm wavelength range showed \u3c 5 μA/W photoresponsivity, corresponding to ISBTs in the valence band. This low photoresponsivity is in part due to insufficient and/or inefficient acceptor dopants (Mg) in QWIP, which in turn, limits the photocurrent generation and overall device performance in the integrated detector-emitter.
Studying dopant concentration and distribution in nm-thick layers by conventional techniques such as secondary ion mass spectrometry (SIMS) is not accurately possible due to SIMS limited analyte volume. Atom probe tomography (APT) was employed to study Mg concentration in layers and interfaces, as well as inside and outside of clusters was analyzed by APT. In addition to information on concentration of Mg and distribution in these nm-thick layers, APT also revealed Mg segregation or clustering in AlGaN/GaN QWIP layers.
Finally, after the design and simulation, growth, fabrication, and characterization of the Mg-doped AlGaN/GaN p-QWIP, the integrated detector-emitter structure was grown and extensive material characterizations using AFM, photoluminescence (PL), XRD, and STEM were performed. The integrated detector-emitter structure utilizes a p-n-p-n thyristor design where QWIP is located as the “gate” or photosensitive part of the npn phototransistor (PT) and InGaN/GaN MQW acts as the “emitter” of the pnp transistor. IR illumination generates photocurrent in the base (QWIP) of the phototransistor. By increasing this current (illumination) at the base of the phototransistor, the voltage on the emitter of the pnp transistor or the MQW emitter increases, leading to light emission in the visible range. I-V characterizations showed the expected thyristor-like behavior on a few devices where there is a knee and by increasing the current, it transitions to a lower resistance state (switching behavior). Additionally, a large number of devices did not show a measurable photocurrent with a diode-like I-V behavior. Our investigations revealed that this is in large part due to carrier capture in the QWIP’s well layers and/or insufficient layer thickness and doping of the p-AlGaN layer, necessitating further design and growth developments in the future to improve device performance.
The research conducted and detailed in this thesis provides insights on multiple fronts, from fundamental design consideration for a realistic AlGaN-based ISBT IR detector, full design consideration and challenges associated with an integrated IR detector-visible emitter based on AlInGaN with their inherent and strong internal polarization field(s), to growth of strained nm scale AlGaN/GaN SL structures and complexity of full integrated device growths-all while facing the challenges of dopant activation in a buried p-doped structure and Mg dopant segregation. The knowledge developed in the thesis is certain to impact not just the specific device detailed here but impactful for development of any AlInGaN/AlInGaN-based SL (MQW) specially in the presence of dopants. These findings on the AlxGa1−xN/GaN superlattice structures not only can be utilized in novel structures based on III-Nitrides such as integrated detector-emitter devices, but also as a platform for any application utilizing these structures such as polarization-enhanced doping, Bragg reflectors, strain management structures, and high electron mobility transistors (HEMTs)
The Excessive Cost of Health: An Analysis of Pharmaceutical Accessibility Issues in the United States
Get PDFCompared to the rest of the world, the United States has one of the worst-performing health care systems. While this is influenced by our hospital systems and clinical care in certain contexts, one of the biggest culprits for our poor ratings is the cost and availability of prescription medications. We pay more than any comparable country for the exact same medications and have a harder time actually accessing them. In this dissertation, I aim to analyze how individuals, companies, and governmental agencies have responded to various instances of high-cost or low-availability prescription medications. To begin, I examine pharmaceutical patenting practices as one potential culprit for the difference in cost suffered by United States citizens. Specifically, I discuss two types of arguments typically used to defend the current patent structure for pharmaceutical products and show that while they may work for patenting generally, they do not justify the current state of pharmaceutical patenting. Then, to demonstrate that the inordinate pricing by the pharmaceutical industry constitutes a moral problem, I turn to two theories of just allocation and apply them to health care goods. I argue that the works of John Rawls and Ronald Dworkin both include a societal obligation to protect the health of citizens, which extends to a right to reasonable access to pharmaceutical products. From there, I move to four examples of ways in which we have dealt with access issues with pharmaceutical goods and discuss whether or not they are justifiable. These include a discussion of whether individuals would be justified in attempting to make their own EpiPens given cost and availability concerns, the rise of online direct-to-consumer pharmaceutical companies, the allocation of unplanned extra doses of COVID-19 vaccines, and concerns with disproportionate difficulties faced by transgender individuals in receiving gender-affirming care
The Psychological Impacts of Homeland Havoc among First-Generation Raised Americans: An Interpretive Phenomenological Analysis
Get PDFThe current study explored the psychological experiences of first-generation raised U.S. citizens whose ancestral homelands are affected by ongoing or recent havoc. First-generation raised Americans are defined as the first-generation to be born in the U.S. or those who immigrated to the U.S. during infancy (less than two years of age). While research on trauma, resilience, and identity has previously addressed collective and intergenerational responses within culturally homogenous groups, few studies have examined the cross-cultural psychological impact of homeland turmoil among diverse diasporic populations living in the U.S.
Using Interpretive Phenomenological Analysis (IPA), this qualitative study employed semi-structured individual interviews and a group member-check/focus group to explore participants’ lived experiences. The final sample included ten individuals from different homelands (i.e., Guatemala, Honduras, Haiti, Sudan, Democratic Republic of the Congo, Palestine, Syria, Yemen, Kashmir, Ukraine), who were selected through purposive and maximum variation sampling to include rich and diverse expressions of the phenomenon. The data were analyzed inductively using IPA\u27s iterative method, with triangulation via participant feedback, a group member check, and auditor review to enhance trustworthiness.
Nine major themes emerged, including: (1) influences on how havoc is experienced, (2) relationship to havoc, (3) havoc effects on relationship to the homeland, (4) relating to homelands, groups, and people, (5) tension between homeland and U.S., (6) identity, (7) inner experience: thoughts, emotions, conflict, (8) professional life effects, and (9) contributing to change: activism, advocacy, allyship. Each of the nine themes carried several subthemes.
Additionally, several points of divergence arose between participants that are explored in further detail. In addition to reviewing past data collected, the group member check also gathered new data and held the role of a focus group between participants with ethnic roots in Ukraine, Sudan, Palestine, and Haiti. The new data obtained highlighted the potential for unexpectedly nourishing connections among those from differing homelands in havoc. The study’s findings can be informative to guide clinicians in individual therapy, group therapy, and assessments. Overall, this study highlights the complex ways homeland havoc psychologically tends to affect individuals in the diaspora from a geographic distance while remaining personally connected
Juror Decision-Making in Context
Get PDFThe United States criminal justice system was designed to be one of fairness, where everyone is equal in the eyes of the law. However, that does not seem to be case, and one instance of this is how a defendant’s gender identity influences juror decision. Much literature exists on juror reaction to the cisgender binary, yet there is a gap in research on how juries react to transgender defendants and how pretrial media exposure interacts with this effect. This study aims to answer this question, as well as look into the interaction of pretrial publicity on juror decision when still accounting for a transgender gender identity. Survey participants were randomly assigned to one of eight total conditions of an experimental survey about a fictitious court case, with the axes of variation being gender identity—cisgender male/female and transgender male/female—and the presence of pretrial publicity. Unfortunately, the final sample size was small (N=158), and no statistically significant results were found. However, the findings suggest that transgender defendants may be disadvantaged in the courtroom. Future research should be carried out with a larger sample size to further explore these issues
Iran-Contra and the Memory of Vietnam: Human Rights, Covert Operations, and the National Security Council
Get PDFIn December of 1972, President Richard Nixon ordered the bombing of North Vietnam, beginning on December 18th and lasting until the 30th. During this period 20,000 tons of bombs were dropped, resulting in the deaths of thousands of Vietnamese. The bombings would soon be known as the “12 Days of Christmas.” Major General Richard Secord, “master of covert operations” sat back and watched as North Vietnam was nearly destroyed. There was nothing that Vietnam could do to combat the U.S. military. Being in Secord’s position, he understood better than anyone that this was far more than a mere phenomenon. For 10 years Secord watched the U.S. Air Force consistently maintain control over Vietnamese airspace, both in the North and the South. To Secord, there was no doubt the United States possessed the capability and fire power to defeat North Vietnam and claim victory in the war
Concurrent Parasympathetic Synchrony in Romantic Couples Exposed to Childhood Maltreatment Subtypes
Get PDFEarly responsive caregiving hones children’s physiological systems and subsequently supports social interactions (Feldman, 2007; Porges 2001; Steelman et al, 2002). Conversely, mis-attuned interactions with caregivers, such as exposure to maltreatment subtypes, might hinder social engagement capacities at both behavioral and biological levels (Kim & Cicchetti, 2004; Sheridan & McLaughlin et al., 2014). These early adverse influences endure across development and can affect behavioral and physiological interactions with romantic partners (Mayo et al., 2021; River et al., 2020; Zamir, 2022). Specifically, temporally coordinated patterns of physiological responses between partners (i.e., synchrony) are linked with important relationship behaviors, including conflict behaviors and relationship satisfaction (Mayo et al., 2021). Couples’ physiological activity may rise and fall at the same time as one another (in-phase synchrony), at alternating times (anti-phase synchrony), or show no significant relation to each other (nonconcordance). The current study investigated the influences of maltreatment subtypes on individual physiological reactivity and romantic partners’ patterns of physiological synchrony. A sample of 61 emerging adults (30 couples) engaged in a research study that collected high frequency heartrate variability (HRV) during a conflict discussion and retrospective reports of exposure to three childhood maltreatment subtypes: physical threat, nonphysical threat, and deprivation. Results revealed no significant associations between maltreatment subtypes and individual HRV reactivity. Maximum nonphysical threat exposure across the couple was predictive of anti-phase HRV synchrony (β =-.49, t(24)=.-2.70, p=.01 R2=.27). Follow-up analyses found a significant interaction such that heterosexual couples with males with higher nonphysical threat exposure and females with lower nonphysical threat exposure were more likely to exhibit anti-phase HRV synchrony values (F(3, 18)=3.51, p=.04 R2=.37, ΔR2=.16). Albeit nonsignificant, the summation of partner’s nonphysical threat exposure scores yielded a medium effect size with the same directionality as the above nonphysical threat finding (β =-.37, t(24)=.-1.94, p=.06, R2=.16). Couples’ physical threat and deprivation scores did not significantly predict HRV synchrony. These findings add to and challenge the existing literature on the implications of HRV reactivity and synchrony patterns. Previous literature shows that physiological functioning can be a moderator for psychotherapy treatment outcomes (Mathewson et al., 2013). As such, results from this study might aid in matching couples to appropriate treatments to reduce severe couple mis-attunement, such as intimate partner violence, and potentially disrupt future cycles of maltreatment
Large Landlords, Code Violations, and Eviction Filing: Evidence from Albany, NY
Get PDFEviction is a major contributor to cycles of urban poverty, and a growing body of research has documented eviction’s harmful effects. This study finds that landlord size and the number of code violations associated with the landlord’s portfolio both predict higher numbers of eviction filings. Using eviction filing data and newly available code violation data from Albany, NY in 2023 and 2024, this study examines landlord characteristics and their association with eviction filing. This study also examines public housing, finding that the Albany Housing Authority is the largest eviction filer in Albany in the study period. These findings are concerning for tenants, as landlord corporatization and financialization has meant that more tenants depend on large, corporate landlords for their housing
Perceptions of Ketamine-Assisted Psychotherapy
Get PDFThis research project tests how educational materials influence individuals’ perceptions of ketamine-assisted psychotherapy (KAP). Previous literature indicates that educational materials shape perceptions of credibility. The hypothesis predicts that education will enhance positive perceptions.
This study recruited participants from Sona Systems and Prolific, with 924 individuals completing the study. The questionnaire gathered demographic information, assessed drug use history, and measured participants’ beliefs about the causes of depression. Participants then evaluated treatment credibility by responding to open-ended questions, the Treatment Adherence/Acceptability Scale (TAAS), the Credibility/Expectancy Questionnaire (CEQ), and the KAP credibility questionnaire.
The results indicate that education does not consistently improve perceptions of KAP. Participants provided significantly more positive spontaneous comments after exposure to the educational materials, but negative comments did not significantly decrease. Attitudes before the intervention did not differ based on beliefs about depression’s causes. However, those who attributed depression to non-biological causes expressed more positive post-intervention responses and greater confidence in treatment effectiveness.
These findings clarify the role of educational materials in shaping attitudes toward mental health treatments. More importantly, they offer insight into current perceptions of KAP and highlight ways to improve educational materials to strengthen support for this treatment. Clearly, KAP will require extensive increases in education to later public perceptions of their credibility
Macroeconomics, State Action, Civic Trust, and Homicide: The Causes and Consequences of Interpersonal Violence in Latin America
Get PDFLatin America and the Caribbean (LAC) represent 8 percent of the global population but about one-third of global homicides, yet interpersonal violence in the region receives limited attention in the English-language literature. This dissertation contains three distinct studies of the causes and consequences of crime and violence in LAC. The first study examines the predictive effects of inflation on robbery, burglary, and homicide rates in Argentina, which possesses one of the highest robbery rates worldwide and has endured high inflation – and, at times, hyperinflation – for years. I obtained annual crime data for 1973-2022 from the National Criminal Information System, homicide data for 1973-2021 from the World Health Organization (WHO), and inflation data from the World Bank. I employed time series models to examine this association. Second, Mexico has an extremely high homicide rate, driven largely by cartel violence, and prior studies in LAC suggested some state interventions may exacerbate, not reduce, violence. I employed panel data for a sample of 2,429 municipalities from 2000 and 2022 to evaluate the impact of military intervention on homicide and gun homicide rates in Mexican municipalities. Using annual homicide data from the National Institute of Statistics and Geography and military intervention data from the Mexican armed forces, I will employ Two-Way-Fixed-Effect (TWFE)-Difference-in-Difference models to determine the impact of military intervention on total homicide and gun homicide rates. Finally, while there are many studies of the causes of variation in national violence rates, there are few studies of the national-level consequences of high violence rates, especially in LAC. I undertook a cross-national study of the effects of the homicide rate on citizens’ trust in the police, the judiciary system, and people in LAC. Using data from 16 LAC nations from 1996 to 2020, homicide data from the WHO, and survey data on trust from Latinobarómetro, I tested for associations via TWFE panel models
Studies on Convexity of DNF Formulae
Get PDFIn this dissertation, we investigate the problem of determining whether a Boolean formula given in disjunctive normal form (DNF) is convex. Although Boolean formulas have various applications, our research focuses on the practical application for rule-based access control policies, where policies are often expressed as a set of Boolean rules. Understanding the structural properties of such formulas is crucial for determining whether a policy can be efficiently represented within a specific access control model.
The main contribution of this research is the conception and analysis of convexity derived from the “gap problem.” In this context, convexity is characterized by the absence of gaps between any two arbitrary terms in a DNF formula, where a gap suggests a missing intermediate assignment that would otherwise bridge the terms within the Boolean space. By formalizing this notion, we derive necessary and sufficient conditions for a DNF formula to be convex, identifying possible differences between any two terms regarding the literals they do and do not share.
In addition to convexity, we discuss related properties, including upward closure and co-convexity. A significant aspect of this research is the development of algorithms for checking these properties. We propose methods and conduct complexity analyses. An important contribution of this research is reducing the verification problem to an instance of the Boolean satisfiability problem (SAT). This allows us to utilize efficient SAT solvers to address these challenges. Additionally, we employ graph-based algorithms on a special subclass of DNF formulas to optimize the verification process of the properties mentioned above