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1. MOCVD growth of β-phase (Al _x Ga _1−x ) ₂ O ₃ on ( 2 ¯01) β-Ga ₂ O ₃ substrates

   https://doi.org/10.1063/5.0025478  

   Bhuiyan, A F; Feng, Zixuan; Johnson, Jared M.; Huang, Hsien-Lien; Hwang, Jinwoo; Zhao, Hongping (October 2020, Applied Physics Letters)

   null (Ed.)
2. β-V ₂ O ₅ as Magnesium Intercalation Cathode

   https://doi.org/10.1021/acsaem.2c02371  

   Trócoli, Rafael; Parajuli, Prakash; Frontera, Carlos; Black, Ashley P.; Alexander, Grant C. B.; Roy, Indrani; Arroyo-de Dompablo, M. Elena; Klie, Robert F.; Cabana, Jordi; Palacín, M. Rosa (October 2022, ACS Applied Energy Materials)
3. Metalorganic chemical vapor deposition of β-(Al _x Ga _1−x ) ₂ O ₃ thin films on (001) β-Ga ₂ O ₃ substrates

   https://doi.org/10.1063/5.0142746  

   Uddin Bhuiyan, A F; Meng, Lingyu; Huang, Hsien-Lien; Sarker, Jith; Chae, Chris; Mazumder, Baishakhi; Hwang, Jinwoo; Zhao, Hongping (April 2023, APL Materials)

   Phase pure β-(Al x Ga 1−x ) 2 O 3 thin films are grown on (001) oriented β-Ga 2 O 3 substrates via metalorganic chemical vapor deposition. By systematically tuning the precursor molar flow rates, the epitaxial growth of coherently strained β-(Al x Ga 1−x ) 2 O 3 films is demonstrated with up to 25% Al compositions as evaluated by high resolution x-ray diffraction. The asymmetrical reciprocal space mapping confirms the growth of coherent β-(Al x Ga 1−x ) 2 O 3 films (x < 25%) on (001) β-Ga 2 O 3 substrates. However, the alloy inhomogeneity with local segregation of Al along the ([Formula: see text]) plane is observed from atomic resolution STEM imaging, resulting in wavy and inhomogeneous interfaces in the β-(Al x Ga 1−x ) 2 O 3 /β-Ga 2 O 3 superlattice structure. Room temperature Raman spectra of β-(Al x Ga 1−x ) 2 O 3 films show similar characteristics peaks as the (001) β-Ga 2 O 3 substrate without obvious Raman shifts for films with different Al compositions. Atom probe tomography was used to investigate the atomic level structural chemistry with increasing Al content in the β-(Al x Ga 1−x ) 2 O 3 films. A monotonous increase in chemical heterogeneity is observed from the in-plane Al/Ga distributions, which was further confirmed via statistical frequency distribution analysis. Although the films exhibit alloy fluctuations, n-type doping demonstrates good electrical properties for films with various Al compositions. The determined valence and conduction band offsets at β-(Al x Ga 1−x ) 2 O 3 /β-Ga 2 O 3 heterojunctions using x-ray photoelectron spectroscopy reveal the formation of type-II (staggered) band alignment. 

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4. Band offsets at metalorganic chemical vapor deposited β-(Al _x Ga _1−x ) ₂ O ₃ /β-Ga ₂ O ₃ interfaces—Crystalline orientation dependence

   https://doi.org/10.1116/6.0001260  

   Bhuiyan, A F; Feng, Zixuan; Huang, Hsien-Lien; Meng, Lingyu; Hwang, Jinwoo; Zhao, Hongping (December 2021, Journal of Vacuum Science & Technology A)
5. Flexible crystalline β-Ga ₂ O ₃ solar-blind photodetectors

   https://doi.org/10.1039/D0TC03740K  

   Lai, Junyu; Hasan, Md Nazmul; Swinnich, Edward; Tang, Zhao; Shin, Sang-Ho; Kim, Munho; Zhang, Peihong; Seo, Jung-Hun (November 2020, Journal of Materials Chemistry C)

   null (Ed.)

   This paper reports the fabrication of β-Ga 2 O 3 nanomembrane (NM) based flexible photodetectors (PDs) and the investigation of their optoelectrical properties under bending conditions. Flexible β-Ga 2 O 3 NM PDs exhibited reliable solar-blind photo-detection under bending conditions. Interestingly, a slight shifting in wavelength of the maximum solar-blind photo-current was observed under the bending condition. To investigate the reason for this peak shifting, the optical properties of β-Ga 2 O 3 NMs under different strain conditions were measured, which revealed changes in the refractive index, extinction coefficient and bandgap of strained β-Ga 2 O 3 NMs due to the presence of nano-sized cracks in the β-Ga 2 O 3 NMs. The results of a multiphysics simulation and a density-functional theory calculation for strained β-Ga 2 O 3 NMs showed that the conduction band minimum and the valence band maximum states were shifted nearly linearly with the applied uniaxial strain, which caused changes in the optical properties of the β-Ga 2 O 3 NM. We also found that nano-gaps in the β-Ga 2 O 3 NM play a crucial role in enhancing the photoresponsivity of the β-Ga 2 O 3 NM PD under bending conditions due to the secondary light absorption caused by reflected light from the nano-gap surfaces. Therefore, this research provides a viable route to realize high-performance flexible photodetectors, which are one of the indispensable components in future flexible sensor systems. 

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