Browsing by Author "Guina, Mircea"

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Bridging the gap between surface physics and photonics
(2024-04) Laukkanen, Pekka; Punkkinen, Marko; Kuzmin, Mikhail; Kokko, Kalevi; Liu, Xiaolong; Radfar, Behrad; Vähänissi, Ville; Savin, Hele; Tukiainen, Antti; Hakkarainen, Teemu; Viheriälä, Jukka; Guina, Mircea
A2 Katsausartikkeli tieteellisessä aikakauslehdessä
Use and performance criteria of photonic devices increase in various application areas such as information and communication, lighting, and photovoltaics. In many current and future photonic devices, surfaces of a semiconductor crystal are a weak part causing significant photo-electric losses and malfunctions in applications. These surface challenges, many of which arise from material defects at semiconductor surfaces, include signal attenuation in waveguides, light absorption in light emitting diodes, non-radiative recombination of carriers in solar cells, leakage (dark) current of photodiodes, and light reflection at solar cell interfaces for instance. To reduce harmful surface effects, the optical and electrical passivation of devices has been developed for several decades, especially with the methods of semiconductor technology. Because atomic scale control and knowledge of surface-related phenomena have become relevant to increase the performance of different devices, it might be useful to enhance the bridging of surface physics to photonics. Toward that target, we review some evolving research subjects with open questions and possible solutions, which hopefully provide example connecting points between photonic device passivation and surface physics. One question is related to the properties of the wet chemically cleaned semiconductor surfaces which are typically utilized in device manufacturing processes, but which appear to be different from crystalline surfaces studied in ultrahigh vacuum by physicists. In devices, a defective semiconductor surface often lies at an embedded interface formed by a thin metal or insulator film grown on the semiconductor crystal, which makes the measurements of its atomic and electronic structures difficult. To understand these interface properties, it is essential to combine quantum mechanical simulation methods. This review also covers metal-semiconductor interfaces which are included in most photonic devices to transmit electric carriers to the semiconductor structure. Low-resistive and passivated contacts with an ultrathin tunneling barrier are an emergent solution to control electrical losses in photonic devices.
GaAs surface passivation for InAs/GaAs quantum dot based nanophotonic devices
(2021-03-26) Chellu, Abhiroop; Koivusalo, Eero; Raappana, Marianna; Ranta, Sanna; Polojärvi, Ville; Tukiainen, Antti; Lahtonen, Kimmo; Saari, Jesse; Valden, Mika; Seppänen, Heli; Lipsanen, Harri; Guina, Mircea; Hakkarainen, Teemu
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Several passivation techniques are developed and compared in terms of their ability to preserve the optical properties of close-to-surface InAs/GaAs quantum dots (QDs). In particular, the influence of N-passivation by hydrazine chemical treatment, N-passivation by hydrazine followed by atomic layer deposition (ALD) of AlOx and use of AlNx deposited by plasma-enhanced ALD are reported. The effectiveness of the passivation is benchmarked by measuring the emission linewidths and decay rates of photo-carriers for the near-surface QDs. All three passivation mechanisms resulted in reducing the oxidation of Ga and As atoms at the GaAs surface and consequently in enhancing the room-temperature photoluminescence (PL) intensity. However, long-term stability of the passivation effect is exhibited only by the hydrazine + AlOx process and more significantly by the AlNx method. Moreover, in contrast to the results obtained from hydrazine-based methods, the AlNx passivation strongly reduces the spectral diffusion of the QD exciton lines caused by charge fluctuations at the GaAs surface. The AlNx passivation is found to reduce the surface recombination velocity by three orders of magnitude (corresponding to an increase of room-temperature PL signal by ∼1030 times). The reduction of surface recombination velocity is demonstrated on surface-sensitive GaAs (100) and the passivating effect is stable for more than one year. This effective method of passivation, coupled with its stability in time, is extremely promising for practical device applications such as quantum light sources based on InAs/GaAs QDs positioned in small-volume photonic cavities and hence in the proximity of GaAs-air interface.
Intracavity double diode structures with GaInP barrier layers for thermophotonic cooling
(2017) Tiira, Jonna; Radevici, Ivan; Haggren, Tuomas; Hakkarainen, Teemu; Kivisaari, Pyry; Lyytikäinen, Jari; Aho, Arto; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani
School of Science | A4 Artikkeli konferenssijulkaisussa
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.
Luminescent (Er,Ho)2O3 thin films by ALD to enhance the performance of silicon solar cells
(2021-01) Ghazy, Amr; Safdar, Muhammad; Lastusaari, Mika; Aho, Arto; Tukiainen, Antti; Savin, Hele; Guina, Mircea; Karppinen, Maarit
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We have fabricated luminescent (Er,Ho)2O3 thin films by atomic layer deposition (ALD) and studied their capability to enhance the performance of state-of-the-art single-junction c-Si bifacial solar cells. The films convert IR photons (e.g. 1523 nm) by three- and two-photon upconversion process to emit visible-light in the 400–700 nm range. When the films were coupled with solar cells, ~3% improvement in the short-circuit current density (620 ± 5 to 638 ± 5 mAcm−2) was recorded under a simulated solar excitation equivalent to 16 suns. These findings highlight a potential of ALD for the design and fabrication of luminescent coatings for practical solar cell devices.
Multiscale in modelling and validation for solar photovoltaics
(2018-10-23) Abu Hamed, Tareq; Adamovic, Nadja; Aeberhard, Urs; Alonso-Alvarez, Diego; Amin-Akhlaghi, Zoe; Maur, Matthias Auf Der; Beattie, Neil; Bednar, Nikola; Berland, Kristian; Birner, Stefan; Califano, Marco; Capan, Ivana; Cerne, Bostjan; Chilibon, Irinela; Connolly, James. P.; Cortes Juan, Frederic; Coutinho, Jose; David, Christin; Deppert, Knut; Donchev, Vesselin; Drev, Marija; Ehlen, Boukje; Ekins-Daukes, Nicholas; Even, Jacky; Fara, Laurentiu; Fuertes Marron, David; Gagliardi, Alessio; Garrido, Blas; Gianneta, Violetta; Gomes, Maria; Guillemoles, Jean-Francois; Guina, Mircea; Halme, Janne; Hocevar, Mateja; Jacak, Lucjan; Jacak, Witold; Jaksic, Zoran; Joseph, Lejo K.; Kassavetis, Spyridon; Kazukauskas, Vaidotas; Kleider, Jean-Paul; Kluczyk, Katarzyna; Kopecek, Radovan; Krasovec, Ursa Opara; Lazzari, Jean-Louis; Lifshitz, Efrat; Loncaric, Martin; Madsen, Soren Peder; Marti Vega, Antonio; Mencaraglia, Denis; Messing, Maria E.; Armando, Felipe Murphy; Nassiopoulou, Androula G.; Neijm, Ahmed; Nemcsics, Akos; Neto, Victor; Pedesseau, Laurent; Persson, Clas; Petridis, Konstantinos; Popescu, Lacramioara; Pucker, Georg; Radovanovic, Jelena; Rimada, Julio C.; Ristova, Mimoza; Savic, Ivana; Savin, Hele; Sendova-Vassileva, Marushka; Sengul, Abdurrahman; Silva, Jose; Steiner, Ullrich; Storch, Jan; Stratakis, Emmanuel; Tao, Shuxia; Tomanek, Pavel; Tomic, Stanko; Tukiainen, Antti; Turan, Rasit; Ulloa, Jose Maria; Wang, Shengda; Yuksel, Fatma; Zadny, Jaroslav; Zarbakhsh, Javad
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic systemcompared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.
Observation of local electroluminescent cooling and identifying the remaining challenges
(2019-01-01) Radevici, Ivan; Sadi, Toufik; Tripurari, Tripathi; Tiira, Jonna; Ranta, Sanna; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani
A4 Artikkeli konferenssijulkaisussa
The cooling of a light emitting diode (LED) by photons carrying out more energy than was used to electrically bias the device, has been predicted decades ago. 1, 2 While this effect, known as electroluminescent cooling (ELC), may allow e.g. fabricating thermophotonic heat pumps (THP) providing higher efficiencies than the existing solid state coolers, 3 ELC at powers sufficient for practical applications is still not demonstrated. To study high-power ELC we use double diode structures (DDSs), which consist of a double heterojunction (DHJ) LED and a photodiode (PD) grown within a single technological process and, thus, enclosed in a cavity with a homogeneous refractive index. 4, 5 The presence of the PD in the structure allows to more directly probe the efficiency of the LED, without the need for light extraction from the system, reducing undesirable losses. Our analysis of experimentally measured I - V curves for both the LED and the PD suggests that the local efficiency of the high-performance LEDs we have fabricated is approximately 110%, exceeding unity over a wide range of injection current densities of up to about 100A/cm 2 . At present the efficiency of the full DDS, however, still falls short of unity, not allowing direct evidence of the extraction of thermal energy from the LED. Here we review our previous studies of DDS for high-power EL cooling and discuss in more detail the remaining bottlenecks for demonstrating high-power ELC in the DDS context: the LED surface states, resistive and photodetection losses. In particular we report our first surface passivation measurements. Further optimization therefore mainly involves reducing the influence of the surface states, e.g. using more efficient surface passivation techniques and optimizing the PD. This combined with the optimization of the DDS layer thicknesses and contact metallization schemes is expected to finally allow purely experimental observation of high-power ELC.
Optical energy transfer and loss mechanisms in coupled intracavity light emitters
(2016) Olsson, Anders; Tiira, Jonna; Partanen, Mikko; Hakkarainen, Teemu; Koivusalo, Eero; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Thermophotonic cooling in GaAs based light emitters
(2019-02-04) Radevici, Ivan; Tiira, Jonna; Sadi, Toufik; Ranta, Sanna; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Fundamental thermodynamic considerations reveal that efficient emission from an electrically injected light emitting diode (LED) can lead to the cooling of the device. This effect, known as electroluminescent (EL) cooling, has been identified decades ago, but it has not been experimentally demonstrated in semiconductors at practical operating conditions due to the extreme requirements set for the efficiency of the light emission. To probe the conditions of EL cooling in GaAs based light emitters, we have designed and fabricated LED structures with integrated photodiodes (PDs), where the optically mediated thermal energy transport between the LED and the PD can be easily monitored. This allows characterization of the fundamental properties of the LED and a path for eliminating selected issues encountered in conventional approaches for EL cooling, such as the challenging light extraction. Despite several remaining nonidealities, our setup demonstrates a very high directly measured quantum efficiency of 70%. To characterize the bulk part of the LED, we also employ a model for estimating the power conversion efficiency (PCE) of the LED, without the contribution of non-fundamental nonidealities such as photodetection losses. Our results suggest that the PCE of the LED peaks at around 105-115%, exceeding the 100% barrier required to reach the EL cooling regime by a clear margin. This implies that the LED component in our device is in fact cooling down by transporting thermal energy carried by the emitted photons to the PD. This provides a compelling incentive for further study to confirm the result and to find ways to extend it for practically useful EL cooling.