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- ItemBulk single crystals and physical properties of β-(AlxGa1-x)2O3(x = 0-0.35) grown by the Czochralski method(Melville, NY : American Inst. of Physics, 2023) Galazka, Zbigniew; Fiedler, Andreas; Popp, Andreas; Ganschow, Steffen; Kwasniewski, Albert; Seyidov, Palvan; Pietsch, Mike; Dittmar, Andrea; Anooz, Saud Bin; Irmscher, Klaus; Suendermann, Manuela; Klimm, Detlef; Chou, Ta-Shun; Rehm, Jana; Schroeder, Thomas; Bickermann, MatthiasWe have systematically studied the growth, by the Czochralski method, and basic physical properties of a 2 cm and 2 in. diameter bulk β-(AlxGa1-x)2O3 single crystal with [Al] = 0-35 mol. % in the melt in 5 mol. % steps. The segregation coefficient of Al in the Ga2O3 melt of 1.1-1.2 results in a higher Al content in the crystals than in the melt. The crystals were also co-doped with Si or Mg. [Al] = 30 mol. % in the melt (33-36 mol. % in the crystals) seems to be a limit for obtaining bulk single crystals of high structural quality suitable for homoepitaxy. The crystals were either semiconducting (no intentional co-dopants with [Al] = 0-30 mol. % and Si-doped with [Al] = 15-20 mol. %), degenerately semiconducting (Si-doped with [Al] ≤ 15 mol. %), or semi-insulating ([Al] ≥ 25 mol. % and/or Mg-doped). The full width at half maximum of the rocking curve was 30-50 arcsec. The crystals showed a linear but anisotropic decrease in all lattice constants and a linear increase in the optical bandgap (5.6 eV for [Al] = 30 mol. %). The room temperature electron mobility at similar free electron concentrations gradually decreases with [Al], presumably due to enhanced scattering at phonons as the result of a larger lattice distortion. In Si co-doped crystals, the scattering is enhanced by ionized impurities. Measured electron mobilities and bandgaps enabled to estimate the Baliga figure of merit for electronic devices.
- ItemPerspectives on MOVPE-grown (100) β-Ga2O3thin films and its Al-alloy for power electronics application([Melville, NY] : American Institute of Physics, 2022) Rehm, Jana; Chou, Ta-Shun; Bin Anooz, Saud; Seyidov, Palvan; Fiedler, Andreas; Galazka, Zbigniew; Popp, AndreasBeta gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor with attractive physical properties for next-generation high-power devices, radio frequency electronics, and solar-blind ultraviolet radiation detectors. Here, we present an overview and perspective on the development of MOVPE-grown (100) β-Ga2O3 thin films and its role in supplementing high-power electronics. We review the development path of the growth process on (100) β-Ga2O3 thin films with a discussion regarding the solved and remaining challenges. The structural defect formation mechanism, substrate treatment strategies, and different growth windows are analyzed to optimize the grown film to fulfill the requirements for device fabrication. Toward industrial applications, MOVPE-grown β-Ga2O3 thin films are evaluated in two aspects: thick layers with smooth surface roughness and the electrical properties in terms of high carrier mobility and low doping concentration. Based on the reviewed results, we propose strategies in substrate preparation treatments and supportive tools such as the machine learning approaches for future growth process optimization and envision the rising interest of the β-Ga2O3-related alloy, β-(AlxGa1-x)2O3.
- ItemSuppression of particle formation by gas-phase pre-reactions in (100) MOVPE-grown β -Ga2O3films for vertical device application(Melville, NY : American Inst. of Physics, 2023) Chou, Ta-Shun; Seyidov, Palvan; Bin Anooz, Saud; Grüneberg, Raimund; Pietsch, Mike; Rehm, Jana; Tran, Thi Thuy Vi; Tetzner, Kornelius; Galazka, Zbigniew; Albrecht, Martin; Irmscher, Klaus; Fiedler, Andreas; Popp, AndreasThis work investigated the metalorganic vapor-phase epitaxy (MOVPE) of (100) β-Ga2O3 films with the aim of meeting the requirements to act as drift layers for high-power electronic devices. A height-adjustable showerhead achieving a close distance to the susceptor (1.5 cm) was demonstrated to be a critical factor in increasing the stability of the Ga wetting layer (or Ga adlayer) on the surface and reducing parasitic particles. A film thickness of up to 3 μm has been achieved while keeping the root mean square below 0.7 nm. Record carrier mobilities of 155 cm2 V-1 s-1 (2.2 μm) and 163 cm2 V-1 s-1 (3 μm) at room temperature were measured for (100) β-Ga2O3 films with carrier concentrations of 5.7 × 1016 and 7.1 × 1016 cm-3, respectively. Analysis of temperature-dependent Hall mobility and carrier concentration data revealed a low background compensating acceptor concentration of 4 × 1015 cm-3.
- ItemHeading for brighter and faster β-Ga2O3 scintillator crystals(Amsterdam : Elsevier, 2022) Drozdowski, Winicjusz; Makowski, Michał; Bachiri, Abdellah; Witkowski, Marcin E.; Wojtowicz, Andrzej J.; Swiderski, Lukasz; Irmscher, Klaus; Schewski, Robert; Galazka, ZbigniewCzochralski-grown β-Ga2O3 and β-Ga2O3:Si crystals with the free electron concentrations between 2.5·1016 and 4.3·1018 cm−3 have been characterized by means of pulse height and scintillation time profile measurements in order to assess their basic scintillation properties. At room temperature, with increasing free electron concentration in the studied range, the scintillation yields decrease from 8920 to 1930 ph/MeV, while the mean scintillation decay times pare down from 989 to 61 ns. However, when the brightest β-Ga2O3 sample is cooled down below 100 K, its scintillation yield exceeds 20000 ph/MeV.
- ItemLow temperature thermoluminescence of β-Ga2O3 scintillator(Amsterdam : Elsevier, 2022) Witkowski, Marcin E.; Drozdowski, Konrad J.; Makowski, Michał; Drozdowski, Winicjusz; Wojtowicz, Andrzej J.; Irmscher, Klaus; Schewski, Robert; Galazka, ZbigniewLow temperature thermoluminescence of β-Ga2O3, β-Ga2O3:Al and β-Ga2O3:Ce has been investigated. Glow curves have been analyzed quantitatively using a rate equations model in order to determine the traps parameters, such as activation energies, capture cross-sections and probabilities of recombination and retrapping.