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  • 1
    In: Applied Physics Letters, AIP Publishing, Vol. 112, No. 3 ( 2018-01-15)
    Abstract: Deep electron and hole traps in 10 MeV proton irradiated high-quality β-Ga2O3 films grown by Hydride Vapor Phase Epitaxy (HVPE) on bulk β-Ga2O3 substrates were measured by deep level transient spectroscopy with electrical and optical injection, capacitance-voltage profiling in the dark and under monochromatic irradiation, and also electron beam induced current. Proton irradiation caused the diffusion length of charge carriers to decrease from 350–380 μm in unirradiated samples to 190 μm for a fluence of 1014 cm−2, and this was correlated with an increase in density of hole traps with optical ionization threshold energy near 2.3 eV. These defects most likely determine the recombination lifetime in HVPE β-Ga2O3 epilayers. Electron traps at Ec-0.75 eV and Ec-1.2 eV present in as-grown samples increase in the concentration after irradiation and suggest that these centers involve native point defects.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 2
    Online Resource
    Online Resource
    American Vacuum Society ; 2017
    In:  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena Vol. 35, No. 3 ( 2017-05-01)
    In: Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, American Vacuum Society, Vol. 35, No. 3 ( 2017-05-01)
    Abstract: Vertical rectifiers fabricated on epi Ga2O3 on bulk β-Ga2O3 were subject to 1.5 MeV electron irradiation at fluences from 1.79 × 1015 to 1.43 × 1016 cm−2 at a fixed beam current of 10−3 A. The electron irradiation caused a reduction in carrier concentration in the epi Ga2O3, with a carrier removal rate of 4.9 cm−1. The 2 kT region of the forward current–voltage characteristics increased due to electron-induced damage, with an increase in diode ideality factor of ∼8% at the highest fluence and a more than 2 order of magnitude increase in on-state resistance. There was a significant reduction in reverse bias current, which scaled with electron fluence. The on/off ratio at −10 V reverse bias voltage was severely degraded by electron irradiation, decreasing from ∼107 in the reference diodes to ∼2 × 104 for the 1.43 × 1016 cm−2 fluence. The reverse recovery characteristics showed little change even at the highest fluence, with values in the range of 21–25 ns for all rectifiers.
    Type of Medium: Online Resource
    ISSN: 2166-2746 , 2166-2754
    RVK:
    Language: English
    Publisher: American Vacuum Society
    Publication Date: 2017
    detail.hit.zdb_id: 3117331-7
    detail.hit.zdb_id: 1475429-0
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  • 3
    Online Resource
    Online Resource
    American Vacuum Society ; 2018
    In:  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena Vol. 36, No. 1 ( 2018-01-01)
    In: Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, American Vacuum Society, Vol. 36, No. 1 ( 2018-01-01)
    Abstract: The electrical performance of vertical geometry Ga2O3 rectifiers was measured before and after 10 MeV proton irradiation at a fixed fluence of 1014 cm−2, as well as subsequent annealing up to 450 °C. Point defects introduced by the proton damage create trap states that reduce the carrier concentration in the Ga2O3, with a carrier removal rate of 235.7 cm−1 for protons of this energy. The carrier removal rates under these conditions are comparable to GaN-based films and heterostructures. Even annealing at 300 °C produces a recovery of approximately half of the carriers in the Ga2O3, while annealing at 450 °C almost restores the reverse breakdown voltage. The on/off ratio of the rectifiers was severely degraded by proton damage and this was only partially recovered by 450 °C annealing. The minority carrier diffusion length decreased from ∼340 nm in the starting material to ∼315 nm after the proton irradiation. The reverse recovery characteristics showed little change with values in the range 20–30 ns before and after proton irradiation.
    Type of Medium: Online Resource
    ISSN: 2166-2746 , 2166-2754
    RVK:
    Language: English
    Publisher: American Vacuum Society
    Publication Date: 2018
    detail.hit.zdb_id: 3117331-7
    detail.hit.zdb_id: 1475429-0
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  • 4
    In: Journal of Applied Physics, AIP Publishing, Vol. 123, No. 18 ( 2018-05-14)
    Abstract: The spatial distribution of electron-hole pair generation in β-Ga2O3 as a function of scanning electron microscope (SEM) beam energy has been calculated by a Monte Carlo method. This spatial distribution is then used to obtain the diffusion length of charge carriers in high-quality epitaxial Ga2O3 films from the dependence of the electron beam induced current (EBIC) collection efficiency on the accelerating voltage of a SEM. The experimental results show, contrary to earlier theory, that holes are mobile in β-Ga2O3 and to a large extent determine the diffusion length of charge carriers. Diffusion lengths in the range 350–400 nm are determined for the as-grown Ga2O3, while processes like exposing the samples to proton irradiation essentially halve this value, showing the role of point defects in controlling minority carrier transport. The pitfalls related to using other popular EBIC-based methods assuming a point-like excitation function are demonstrated. Since the point defect type and the concentration in currently available Ga2O3 are dependent on the growth method and the doping concentration, accurate methods of diffusion length determination are critical to obtain quantitative comparisons of material quality.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 5
    In: Energy Technology, Wiley, Vol. 4, No. 11 ( 2016-11), p. 1463-1468
    Abstract: Achieving high‐specific‐power and radiation hardness of solar cells is of great importance to perform tasks and achieve duration in space. Therefore, we investigated the proton irradiation resistance of ultralightweight CdS/CdTe thin film solar cells having high specific power values. High‐energy proton beams (15 MeV) with doses ranging from 1×10 12 to 1×10 15  cm −2 were used, equivalent to more than 2000 years in low Earth orbit. Although 70 % decrease in cell conversion efficiency was observed after proton irradiation with dose of 1×10 15  cm −2 , it still maintained the photovoltaic performance. The specific power of the fabricated cell decreased from 358 W kg −1 to 109 W kg −1 after proton irradiation (dose=1×10 15  cm −2 ), which is still comparable to specific powers of other types of solar cells. Our work indicated that reduction of short circuit current is a major factor of deterioration of the cell performance under the high energy proton irradiation. This work revealed that our lightweight CdS/CdTe solar cells have significant potential for the use in space applications: reduction of launch cost by achieving high specific power and assurance of durability over prolonged space missions.
    Type of Medium: Online Resource
    ISSN: 2194-4288 , 2194-4296
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 2700412-0
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  • 6
    In: Energy Technology, Wiley, Vol. 4, No. 11 ( 2016-11), p. 1328-1328
    Type of Medium: Online Resource
    ISSN: 2194-4288 , 2194-4296
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 2700412-0
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  • 7
    In: Applied Physics Letters, AIP Publishing, Vol. 102, No. 16 ( 2013-04-22)
    Abstract: We demonstrated three-dimensional (3D) graphene foam-based transparent conductive electrodes in GaN-based blue light-emitting diodes (LEDs). A 3D graphene foam structure grown on 3D Cu foam using a chemical vapor deposition method was transferred onto a p-GaN layer of blue LEDs. Optical and electrical performances were greatly enhanced by employing 3D graphene foam as transparent conductive electrodes in blue LED devices, which were analyzed by electroluminescence measurements, micro-Raman spectroscopy, and light intensity-current-voltage testing. The forward operating voltage and the light output power at an injection current of 100 mA of the GaN-based blue LEDs with a graphene foam-based transparent conductive electrode were improved by ∼26% and ∼14%, respectively. The robustness, high transmittance, and outstanding conductivity of 3D graphene foam show great potentials for advanced transparent conductive electrodes in optoelectronic devices.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 8
    Online Resource
    Online Resource
    American Vacuum Society ; 2016
    In:  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena Vol. 34, No. 4 ( 2016-07-01)
    In: Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, American Vacuum Society, Vol. 34, No. 4 ( 2016-07-01)
    Abstract: Planar thin film β-Ga2O3 photodetectors were irradiated with 5 MeV protons at doses from 1013 to 1015 cm−2, and the resulting effects on photocurrent, responsivity, quantum efficiency, and photo-to-dark current ratio at 254 nm wavelength were measured at both 25 and 150 °C. The photocurrent increased with dose due to the introduction of damage from nonionizing energy loss by the protons. The total calculated vacancy concentration increased from 5 × 1015 to 5 × 1017 cm−3 over the dose range investigated. The dark current increased in proportion with the implant dose, leading to a decrease in the ratio of photocurrent to dark current. The photocurrent induced by 254 nm illumination increased with dose, from ∼0.3 × 10−7 A at 25 °C for a dose of 1013 cm−2 to ∼10−6 A at a dose of 1015 cm−2 at a fixed light intensity of 760 μW/cm2. The photo-to-dark current ratio decreased from ∼60 in the control samples to ∼9 after proton doses of 1015 cm−2, with corresponding external quantum efficiencies of ∼103% in control samples, ∼2 × 103% for a dose of 1013 cm−2, and 104% for a dose of 1015 cm−2. The mechanism for the increase in photocurrent is the introduction of gap states, since the dark current of the photodetectors was increased by illuminating with sub-bandgap (red or green laser light) for the proton irradiated samples.
    Type of Medium: Online Resource
    ISSN: 2166-2746 , 2166-2754
    RVK:
    Language: English
    Publisher: American Vacuum Society
    Publication Date: 2016
    detail.hit.zdb_id: 3117331-7
    detail.hit.zdb_id: 1475429-0
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  • 9
    Online Resource
    Online Resource
    American Vacuum Society ; 2018
    In:  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena Vol. 36, No. 4 ( 2018-07-01)
    In: Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, American Vacuum Society, Vol. 36, No. 4 ( 2018-07-01)
    Abstract: The effects of 18 MeV alpha particle irradiation dose on the electrical properties of SiNx/AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs) using in situ grown silicon nitride as the gate dielectric were investigated. The MISHEMT devices were irradiated with alpha particles at doses of 1 × 1012 or 1 × 1013 cm−2 at a fixed energy of 18 MeV. Device performance degradation was more prominent for the irradiated samples under high frequency operation. At a frequency of 100 kHz and gate voltage pulsed from −6 to 3 V, the saturation drain current reduction was 32% and 41% after alpha irradiation doses of 1 × 1012 and 1 × 1013 cm−2, respectively. The drain current reduction at 100 kHz also depended on the duty cycle. At higher duty cycles, the drain current reduction was less severe. The calculated carrier removal rates were in the range of 2062–2175 cm−1 for the alpha doses studied. The results demonstrate the capability of AlGaN/GaN MISHEMTs in environments where resilience to radiation is required.
    Type of Medium: Online Resource
    ISSN: 2166-2746 , 2166-2754
    RVK:
    Language: English
    Publisher: American Vacuum Society
    Publication Date: 2018
    detail.hit.zdb_id: 3117331-7
    detail.hit.zdb_id: 1475429-0
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  • 10
    Online Resource
    Online Resource
    Optica Publishing Group ; 2015
    In:  Optics Express Vol. 23, No. 19 ( 2015-09-21), p. A1081-
    In: Optics Express, Optica Publishing Group, Vol. 23, No. 19 ( 2015-09-21), p. A1081-
    Type of Medium: Online Resource
    ISSN: 1094-4087
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2015
    detail.hit.zdb_id: 1491859-6
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