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    Developing ethical and transparent artificial intelligence algorithms to support decision making in healthcare based on brain research and personal care events of patients
    (Aalto University, 2022) Lahti, Lauri; Tietotekniikan laitos; Department of Computer Science; Perustieteiden korkeakoulu; School of Science
    We propose a new research methodology that develops ethical and transparent artificial intelligence algorithms to support decision making in healthcare. This development relies on a diverse statistical and data analysis methodology based on real-life data gathered in brain research and care events of different patient groups. The proposed new research methodology is created, developed and carried out in a broad international multidisciplinary research collaboration with various patient and disabled people's groups, healthcare professionals, educational institutions, and laboratory measurements of experimental brain research conducted at a biomedical research institute. The proposed new research methodology is motivated by the previous research that has given successful classification results with various bio-inspired artificial intelligence algorithms, based on unsupervised learning (such as various clustering algorithms) and supervised learning (such as artificial neural network algorithms) that are implemented following the structural and functional principles of real-life living biological tissues.
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    Supporting care by interpretation of expressions about patient experience with machine learning
    (IJNTR Journals, 2018) Lahti, Lauri; Tietotekniikan laitos; Department of Computer Science; Perustieteiden korkeakoulu; School of Science
    Our research aims at addressing the needs of developing data analysis about communication in respect to care seeking and primary care, discovering how health expressions evolve along the personal growth and learning process, and how to solve the needs identified in respect to developing measuring the quality of life. We provide an overview of the development of a new research methodology exploiting machine learning for analyzing patient experience expressions to support personalized care and managing in everyday life. Our research relies on an online questionnaire in which the representatives of various population groups perform interpretation tasks. Dependencies between answers about the interpretation tasks and background information are analyzed with machine learning methods. The research creates new ways to interpret and address the meanings of language usage of different groups of patients and impaired carefully and distinctively as a part of everyday life and care events.
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    Silicon-Integrated III–V Light Emitters and Absorbers Using Bipolar Diffusion
    (American Physical Society (APS), 2020) Kivisaari, Pyry; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Engineered Nanosystems Group; Perustieteiden korkeakoulu; School of Science
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    How players across gender and age experience Pokémon Go?
    (Springer Science and Business Media LLC, 2019) Malik, Aqdas; Hiekkanen, Kari; Hussain, Zaheer; Hamari, Juho; Johri, Aditya; Tietotekniikan laitos; Department of Computer Science; Strategic Usability group; Perustieteiden korkeakoulu; School of Science
    The purpose of this study is to provide insights into player experiences and motivations in Pokémon Go, a relatively new phenomenon of location-based augmented reality games. With the increasing usage and adoption of various forms of digital games worldwide, investigating the motivations for playing games has become crucial not only for researchers but for game developers, designers, and policy makers. Using an online survey (N = 1190), the study explores the motivational, usage, and privacy concerns variations among age and gender groups of Pokémon Go players. Most of the players, who are likely to be casual gamers, are persuaded toward the game due to nostalgic association and word of mouth. Females play Pokémon Go to fulfill physical exploration and enjoyment gratifications. On the other hand, males seek to accomplish social interactivity, achievement, coolness, and nostalgia gratifications. Compared to females, males are more concerned about the privacy aspects associated with the game. With regard to age, younger players display strong connotation with most of the studied gratifications and the intensity drops significantly with an increase in age. With the increasing use of online and mobile games worldwide among all cohorts of society, the study sets the way for a deeper analysis of motivation factors with respect to age and gender. Understanding motivations for play can provide researchers with the analytic tools to gain insight into the preferences for and effects of game play for different kinds of users.
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    Electroluminescent cooling in intracavity light emitters: modeling and experiments
    (Springer Nature, 2017) Sadi, Toufik; Kivisaari, Pyry; Tiira, Jonna; Radevici, Ivan; Haggren, Tuomas; Oksanen, Jani; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Engineered Nanosystems; Perustieteiden korkeakoulu; School of Science
    We develop a coupled electronic charge and photon transport simulation model to allow for deeper analysis of our recent experimental studies of intracavity double diode structures (DDSs). The studied structures consist of optically coupled AlGaAs/GaAs double heterojunction light emitting diode (LED) and GaAs p–n-homojunction photodiode (PD) structure, integrated as a single semiconductor device. The drift–diffusion formalism for charge transport and an optical model, coupling the LED and the PD, are self-consistently applied to complement our experimental work on the evaluation of the efficiency of these DDSs. This is to understand better their suitability for electroluminescent cooling (ELC) demonstration, and shed further light on electroluminescence and optical energy transfer in the structures. The presented results emphasize the adverse effect of non-radiative recombination on device efficiency, which is the main obstacle for achieving ELC in III-V semiconductors.
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    Influence of photo-generated carriers on current spreading in double diode structures for electroluminescent cooling
    (IOP Publishing, 2018) Radevici, Ivan; Tiira, Jonna; Sadi, Toufik; Oksanen, Jani; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Engineered Nanosystems Group; Engineered Nanosystems Group; Perustieteiden korkeakoulu; School of Science
    Current crowding close to electrical contacts is a common challenge in all optoelectronic devices containing thin current spreading layers (CSLs). We analyze the effects of current spreading on the operation of the so-called double diode structure (DDS), consisting of a light emitting diode (LED) and a photodiode (PD) fabricated within the same epitaxial growth process, and providing an attractive platform for studying electroluminescent (EL) cooling under high bias conditions. We show that current spreading in the common n-type layer between the LED and the PD can be dramatically improved by the strong optical coupling between the diodes, as the coupling enables a photo-generated current through the PD. This reduces the current in the DDS CSL and enables studying EL cooling using structures that are not limited by the conventional light extraction challenges encountered in normal LEDs. The current spreading in the structures is studied using optical imaging techniques, electrical measurements, simulations, as well as simple equivalent circuit models developed for this purpose. The improved current spreading leads further to a mutual dependence with the coupling efficiency, which is expected to facilitate the process of optimizing the DDS. We also report a new improved value of 63% for the DDS coupling quantum efficiency (CQE).
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    Sharper Upper Bounds for Unbalanced Uniquely Decodable Code Pairs
    (Institute of Electrical and Electronics Engineers (IEEE), 2018) Austrin, Per; Kaski, Petteri; Koivisto, Mikko; Nederlof, Jesper; Tietotekniikan laitos; Department of Computer Science; Perustieteiden korkeakoulu; School of Science
    Two sets of 0-1 vectors of fixed length form a uniquely decodeable code pair if their Cartesian product is of the same size as their sumset, where the addition is pointwise over integers. For the size of the sumset of such a pair, van Tilborg has given an upper bound in the general case. Urbanke and Li, and later Ordentlich and Shayevitz, have given better bounds in the unbalanced case, that is, when either of the two sets is sufficiently large. Improvements to the latter bounds are presented.
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    Elimination of Lateral Resistance and Current Crowding in Large-Area LEDs by Composition Grading and Diffusion-Driven Charge Transport
    (Wiley-Blackwell, 2017) Kivisaari, Pyry; Kim, Iurii; Suihkonen, Sami; Oksanen, Jani; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Perustieteiden korkeakoulu; School of Science
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    Two-phase model of hydrogen transport to optimize nanoparticle catalyst loading for hydrogen evolution reaction
    (Elsevier BV, 2016) Kemppainen, Erno; Halme, Janne; Hansen, Ole; Seger, Brian; Lund, Peter D.; Teknillisen fysiikan laitos; Department of Applied Physics; New Energy Technologies (Renewable); Perustieteiden korkeakoulu; School of Science
    With electrocatalysts it is important to be able to distinguish between the effects of mass transport and reaction kinetics on the performance of the catalyst. When the hydrogen evolution reaction (HER) is considered, an additional and often neglected detail of mass transport in liquid is the evolution and transport of gaseous H2, since HER leads to the continuous formation of H2 bubbles near the electrode. We present a numerical model that includes the transport of both gaseous and dissolved H2, as well as mass exchange between them, and combine it with a kinetic model of HER at platinum (Pt) nanoparticle electrodes. We study the effect of the diffusion layer thickness and H2 dissolution rate constant on the importance of gaseous transport, and the effect of equilibrium hydrogen coverage and Pt loading on the kinetic and mass transport overpotentials. Gaseous transport becomes significant when the gas volume fraction is sufficiently high to facilitate H2 transfer to bubbles within a distance shorter than the diffusion layer thickness. At current densities below about 40 mA/cm2 the model reduces to an analytical approximation that has characteristics similar to the diffusion of H2. At higher current densities the increase in the gas volume fraction makes the H2 surface concentration nonlinear with respect to the current density. Compared to the typical diffusion layer model, our model is an extension that allows more detailed studies of reaction kinetics and mass transport in the electrolyte and the effects of gas bubbles on them.
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    Squeezing of Quantum Noise of Motion in a Micromechanical Resonator
    (American Physical Society (APS), 2015) Pirkkalainen, J.-M.; Damskägg, E.; Brandt, M.; Massel, F.; Sillanpää, M. A.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
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    Interpretation of health-related expressions and dialogues: enabling personalized care with contextual measuring and machine learning
    (Aalto University, 2017) Lahti, Lauri; Tietotekniikan laitos; Department of Computer Science; Perustieteiden korkeakoulu; School of Science
    We propose a new research framework that develops a method for interpretation of health-related expressions and dialogues to enable personalized care with contextual measuring and machine learning. The new research framework is implemented with a research project that gathers from various patient groups and other population groups a broad collection of essential perspectives towards health and well-being. In experimental setups persons (for example patients, their family members and representatives of care personnel) are asked to classify a given set of expressions (linguistic statements, image materials or other stimuli) into different categories, and these categorizations are then used as input vectors for computational models. To develop the method a central task is to classify with machine learning models health-related expressions and dialogues in respect to various events, processes and persons in healthcare. Our experimental results based on a sample of context-based linguistic health data indicated fruitful possibilities for gaining classifications of essential traits of language usage, appearance and activity for persons of diverse population groups based on various scales, perspectives, background assumptions and contexts.
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    Off-the-Hook: An Efficient and Usable Client-Side Phishing Prevention Application
    (IEEE, 2017) Marchal, Samuel; Armano, Giovanni; Grondahl, Tommi; Saari, Kalle; Singh, Nidhi; Asokan, N.; Tietotekniikan laitos; Department of Computer Science; Secure Systems; Perustieteiden korkeakoulu; School of Science
    Phishing is a major problem on the Web. Despite the significant attention it has received over the years, there has been no definitive solution. While the state-of-the-art solutions have reasonably good performance, they suffer from several drawbacks including potential to compromise user privacy, difficulty of detecting phishing websites whose content change dynamically, and reliance on features that are too dependent on the training data. To address these limitations we present a new approach for detecting phishing webpages in real-time as they are visited by a browser. It relies on modeling inherent phisher limitations stemming from the constraints they face while building a webpage. Consequently, the implementation of our approach, Off-the-Hook, exhibits several notable properties including high accuracy, brand-independence and good language-independence, speed of decision, resilience to dynamic phish and resilience to evolution in phishing techniques. Off-the-Hook is implemented as a fully-client-side browser add-on, which preserves user privacy. In addition, Off-the-Hook identifies the target website that a phishing webpage is attempting to mimic and includes this target in its warning. We evaluated Off-the-Hook in two different user studies. Our results show that users prefer Off-the-Hook warnings to Firefox warnings.
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    Effect of Alkali Metal Atom Doping on the CuInSe2-Based Solar Cell Absorber
    (American Chemical Society (ACS), 2017) Malitckaya, M.; Komsa, H.-P.; Havu, V.; Puska, M. J.; Teknillisen fysiikan laitos; Department of Applied Physics; Electronic properties of materials (EPM); Perustieteiden korkeakoulu; School of Science
    The efficiency of Cu(In,Ga)Se_2 (CIGS)-based solar cells can bemarkedly improved by controlled introduction of alkali metal (AM) atomsusing post-deposition treatment (PDT) after CIGS growth. Previous studieshave indicated that AM atoms may act as impurities or agglomerate intosecondary phases. To enable further progress, understanding of atomic levelprocesses responsible for these improvements is required. To this end, we haveinvestigated theoretically the effects of the AM elements Li, Na, K, Rb, and Cson the properties of the parent material CuInSe_2 . First, the effects of the AMimpurities in CuInSe_2 have been investigated in terms of formation energies,charge transition levels, and migration energy barriers. We found that AM atoms preferentially substitute for Cu atoms at theneutral charge state. Under In-poor conditions, AM atoms at the In site also show low formation energies and are acceptors. Themigration energy barriers show that the interstitial diffusion mechanism may be relevant only for Li, Na, and K, whereas all theAM atoms can diffuse with the help of Cu vacancies. The competition between these two mechanisms strongly depends on theconcentration of Cu vacancies. We also discuss how AM atoms can contribute to increasing Cu-depleted regions. Second, AMatoms can form secondary phases with Se and In atoms. We suggest a mechanism for the secondary phase formation followingthe PDT process. On the basis of the calculated reaction enthalpies and migration considerations, we find that mixed phases aremore likely in the case of LiInSe_2 and NaInSe_2 , whereas formation of secondary phases is expected for KInSe_2 , RbInSe_2 , andCsInSe_2 . We discuss our findings in the light of experimental results obtained for AM treatments. The secondary phases havelarge energy band gaps and improve the morphology of the buffer surface by enabling a favorable band alignment, which canimprove the electrical properties of the device. Moreover, they can also passivate the surface by forming a diffusion barrier.Overall, our work points to different roles played by the light and heavy AM atoms and suggests that both types may be neededto maximize their benefits on the solar cell performance.
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    Uses and Gratifications of digital photo sharing on Facebook
    (Elsevier BV, 2015) Malik, Aqdas; Dhir, Amandeep; Nieminen, Marko; Tietotekniikan laitos; Department of Computer Science; Strategic Usability Group (STRATUS); Perustieteiden korkeakoulu; School of Science
    Despite the rapid adoption of Facebook as a means of photo sharing, minimal research has been conducted to understand user gratification behind this activity. In order to address this gap, the current study examines users’ gratifications in sharing photos on Facebook by applying Uses and Gratification (U&G) theory. An online survey completed by 368 respondents identified six different gratifications, namely, affection, attention seeking, disclosure, habit, information sharing, and social influence, behind sharing digital photos on Facebook. Some of the study’s prominent findings were: age was in positive correlation with disclosure and social influence gratifications; gender differences were identified among habit and disclosure gratifications; number of photos shared was negatively correlated with habit and information sharing gratifications. The study’s implications can be utilized to refine existing and develop new features and services bridging digital photos and social networking services.
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    Know Your Phish: Novel Techniques for Detecting Phishing Sites and Their Targets
    (IEEE, 2016) Marchal, Samuel; Saari, Kalle; Singh, Nidhi; Asokan, N.; Tietotekniikan laitos; Department of Computer Science; Secure Systems; Perustieteiden korkeakoulu; School of Science
    Phishing is a major problem on the Web. Despite the significant attention it has received over the years, there has been no definitive solution. While the state-of-the-art solutions have reasonably good performance, they require a large amount of training data and are not adept at detecting phishing attacks against new targets. In this paper, we begin with two core observations: (a) although phishers try to make a phishing webpage look similar to its target, they do not have unlimited freedom in structuring the phishing webpage, and (b) a webpage can be characterized by a small set of key terms, how these key terms are used in different parts of a webpage is different in the case of legitimate and phishing webpages. Based on these observations, we develop a phishing detection system with several notable properties: it requires very little training data, scales well to much larger test data, is language-independent, fast, resilient to adaptive attacks and implemented entirely on client-side. In addition, we developed a target identification component that can identify the target website that a phishing webpage is attempting to mimic. The target detection component is faster than previously reported systems and can help minimize false positives in our phishing detection system.
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    Previous exposure to intact speech increases intelligibility of its digitally degraded counterpart as a function of stimulus complexity
    (Elsevier BV, 2015) Hakonen, Maria; May, Patrick J.C.; Alho, Jussi; Alku, Paavo; Jokinen, Emma; Jääskeläinen, Iiro P.; Tiitinen, Hannu; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Brain and Mind laboratory; Aivot ja Mieli laboratorio; Perustieteiden korkeakoulu; School of Science
    Recent studies have shown that acoustically distorted sentences can be perceived as either unintelligible or intelligible depending on whether one has previously been exposed to the undistorted, intelligible versions of thesentences. This allows studying processes specifically related to speech intelligibility since any change betweenthe responses to the distorted stimuli before and after the presentation of their undistorted counterparts cannotbe attributed to acoustic variability but, rather, to the successful mapping of sensory information onto memoryrepresentations. To estimate how the complexity of the message is reflected in speech comprehension, we appliedthis rapid change in perception to behavioral and magnetoencephalography (MEG) experiments usingvowels, words and sentences. In the experiments, stimuli were initially presented to the subject in a distortedform, after which undistorted versions of the stimuli were presented. Finally, the original distorted stimuliwere presented once more. The resulting increase in intelligibility observed for the second presentation of thedistorted stimuli depended on the complexity of the stimulus: vowels remained unintelligible (behaviorallymeasured intelligibility 27%) whereas the intelligibility of the words increased from 19% to 45% and that of thesentences from31% to 65%. This increase in the intelligibility of the degraded stimuliwas reflected as an enhancementof activity in the auditory cortex and surrounding areas at early latencies of 130–160 ms. In the same regions,increasing stimulus complexity attenuated mean currents at latencies of 130–160 ms whereas atlatencies of 200–270 ms the mean currents increased. These modulations in cortical activity may reflect feedbackfromtop-down mechanismsenhancing the extraction of information fromspeech. The behavioral results suggestthat memory-driven expectancies can have a significant effect on speech comprehension, especially in acousticallyadverse conditions where the bottom-up information is decreased.
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    Review of energy system flexibility measures to enable high levels of variable renewable electricity
    (Elsevier BV, 2015) Lund, Peter D.; Lindgren, Juuso; Mikkola, Jani; Salpakari, Jyri; Teknillisen fysiikan laitos; Department of Applied Physics; New Energy Technologies; Perustieteiden korkeakoulu; School of Science
    The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.
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    Elimination of resistive losses in large-area LEDs by new diffusion-driven devices
    (SPIE, 2017) Kivisaari, Pyry; Kim, Iurii; Suihkonen, Sami; Oksanen, Jani; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Perustieteiden korkeakoulu; School of Science
    High-power operation of conventional GaN-based light-emitting diodes (LEDs) is severely limited by current crowding, which increases the bias voltage of the LED, concentrates light emission close to the p-type contact edge, and aggravates the efficiency droop. Fabricating LEDs on thick n-GaN substrates alleviates current crowding but requires the use of expensive bulk GaN substrates and fairly large n-contacts, which take away a large part of the active region (AR). In this work, we demonstrate through comparative simulations how the recently introduced diffusion-driven charge transport (DDCT) concept can be used to realize lateral heterojunction (LHJ) structures, which eliminate most of the lateral current crowding. Specifically in this work, we analyze how using a single-side graded AR can both facilitate electron and hole diffusion in DDCT and increase the effective AR thickness. Our simulations show that the increased effective AR thickness allows a substantial reduction in the efficiency droop at large currents, and that unlike conventional 2D LEDs, the LHJ structure shows practically no added efficiency loss or differential resistance due to current crowding. Furthermore, as both electrons and holes enter the AR from the same side without any notable potential barriers in the LHJ structure, the LHJ structure shows an additional wall-plug efficiency gain over the conventional structures under comparison. This injection from the same side is expected to be even more interesting in multiple quantum well structures, where carriers typically need to surpass several potential barriers in conventional LEDs before recombining. In addition to simulations, we also demonstrate selective-area growth of a finger structure suitable for operation as an LHJ device with 2µm distance between n- and p-GaN regions.
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    Lock-in thermography approach for imaging the efficiency of light emitters and optical coolers
    (SPIE, 2017) Radevici, Ivan; Tiira, Jonna; Oksanen, Jani; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Perustieteiden korkeakoulu; School of Science
    Developing optical cooling technologies requires access to reliable efficiency measurement techniques and ability to detect spatial variations in the efficiency and light emission of the devices. We investigate the possibility to combine the calorimetric efficiency measurement principles with lock-in thermography (LIT) and conventional luminescence microscopy to enable spatially resolved measurement of the efficiency, current spreading and local device heating of double diode structures (DDS) serving as test vessels for developing thermophotonic cooling devices. Our approach enables spatially resolved characterization and localization of the losses of the double diode structures as well as other light emitting semiconductor devices. In particular, the approach may allow directly observing effects like current crowding and surface recombination on the light emission and heating of the DDS devices.
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    Intracavity double diode structures with GaInP barrier layers for thermophotonic cooling
    (SPIE, 2017) Tiira, Jonna; Radevici, Ivan; Haggren, Tuomas; Hakkarainen, Teemu; Kivisaari, Pyry; Lyytikäinen, Jari; Aho, Arto; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani; Neurotieteen ja lääketieteellisen tekniikan laitos; Department of Neuroscience and Biomedical Engineering; Perustieteiden korkeakoulu; School of Science
    Optical cooling of semiconductors has recently been demonstrated both for optically pumped CdS nanobelts and for electrically injected GaInAsSb LEDs at very low powers. To enable cooling at larger power and to understand and overcome the main obstacles in optical cooling of conventional semiconductor structures, we study thermophotonic (TPX) heat transport in cavity coupled light emitters. Our structures consist of a double heterojunction (DHJ) LED with a GaAs active layer and a corresponding DHJ or a p-n-homojunction photodiode, enclosed within a single semiconductor cavity to eliminate the light extraction challenges. Our presently studied double diode structures (DDS) use GaInP barriers around the GaAs active layer instead of the AlGaAs barriers used in our previous structures. We characterize our updated double diode structures by four point probe IV- measurements and measure how the material modifications affect the recombination parameters and coupling quantum efficiencies in the structures. The coupling quantum efficiency of the new devices with InGaP barrier layers is found to be approximately 10 % larger than for the structures with AlGaAs barriers at the point of maximum efficiency.