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1. Electrical and Structural Analysis of β ‐Ga 2 O 3 /GaN Wafer‐Bonded Heterojunctions with a ZnO Interlayer

   https://doi.org/10.1002/aelm.202300174  

   Jian, Zhe ; Sun, Kai ; Kosanovic, Stefan ; Clymore, Christopher J. ; Mishra, Umesh ; Ahmadi, Elaheh ( June 2023 , Advanced Electronic Materials)

   Wafer bonding ofβ‐Ga₂O₃and N‐polar GaN single crystal substrates is demonstrated by adding ZnO as a “glue” interlayer. The wafers are fully bonded such that Newton rings are not observed. Temperature‐dependent current‐voltage (I–V) measurements are conducted on the as‐bonded Ga₂O₃/ZnO/N‐polar GaN test structure and after annealing at 600 °C and 1100 °C. The impact of post‐annealing temperature on the electrical and structural characteristics of the bonded samples is investigated. A consistently ohmic‐like characteristic is obtained by annealing the bonded wafers at 1100 °C in N_2,which is in part due to crystallization of ZnO and diffusion of Ga into ZnO which makes it n‐type doped. The wafer bonding ofβ‐Ga₂O₃and GaN achieved in this work is promising to combine the material merits of both GaN and Ga₂O₃targeting breakthrough high‐frequency and high‐power device performances.

    

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2. TCAD Simulation Models, Parameters, and Methodologies for β-Ga 2 O 3 Power Devices

   https://doi.org/10.1149/2162-8777/accfbe  

   Wong, Hiu Yung ( May 2023 , ECS Journal of Solid State Science and Technology)

   β-Ga₂O₃is an emerging material and has the potential to revolutionize power electronics due to its ultra-wide-bandgap (UWBG) and lower native substrate cost compared to Silicon Carbide and Gallium Nitride. Sinceβ-Ga₂O₃technology is still not mature, experimental study ofβ-Ga₂O₃is difficult and expensive. Technology-Computer-Aided Design (TCAD) is thus a cost-effective way to study the potentials and limitations ofβ-Ga₂O₃devices. In this paper, TCAD parameters calibrated to experiments are presented. They are used to perform the simulations in heterojunction p-NiO/n-Ga₂O₃diode, Schottky diode, and normally-off Ga₂O₃vertical FinFET. Besides the current-voltage (I-V) simulations, breakdown, capacitance-voltage (C-V), and short-circuit ruggedness simulations with robust setups are discussed. TCAD Sentaurus is used in the simulations but the methodologies can be applied in other simulators easily. This paves the road to performing a holistic study ofβ-Ga₂O₃devices using TCAD.

    

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3. In Situ Dielectric Al 2 O 3 /β‐Ga 2 O 3 Interfaces Grown Using Metal–Organic Chemical Vapor Deposition

   https://doi.org/10.1002/aelm.202100333  

   Roy, Saurav ; Chmielewski, Adrian E. ; Bhattacharyya, Arkka ; Ranga, Praneeth ; Sun, Rujun ; Scarpulla, Michael A. ; Alem, Nasim ; Krishnamoorthy, Sriram ( August 2021 , Advanced Electronic Materials)

   High quality dielectric‐semiconductor interfaces are critical for reliable high‐performance transistors. This paper reports the in situ metal–organic chemical vapor deposition of Al₂O₃on β‐Ga₂O₃as a potentially better alternative to the most commonly used atomic layer deposition (ALD). The growth of Al₂O₃is performed in the same reactor as Ga₂O₃using trimethylaluminum and O₂as precursors without breaking the vacuum at a growth temperature of 600 °C. The fast and slow near interface traps at the Al₂O₃/β‐Ga₂O₃interface are identified and quantified using stressed capacitance–voltage (CV) measurements on metal oxide semiconductor capacitor (MOSCAP) structures. The density of shallow and deep level initially filled traps (D_it) are measured using ultraviolet‐assisted CV technique. The average D_itfor the MOSCAP is determined to be 6.4×10¹¹cm⁻²eV⁻¹. The conduction band offset of the Al₂O₃/ Ga₂O₃interface is also determined from CV measurements and found out to be 1.7 eV which is in close agreement with the existing literature reports of ALD Al₂O₃/Ga₂O₃interface. The current–voltage characteristics are also analyzed and the average breakdown field is extracted to be approximately 5.8 MV cm⁻¹. This in situ Al₂O₃dielectric on β‐Ga₂O₃with improved dielectric properties can enable Ga₂O₃‐based high‐performance devices.

    

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4. Ga + -focused ion beam damage in n-type Ga 2 O 3

   https://doi.org/10.1116/5.0099892  

   Xia, Xinyi ; Al-Mamun, Nahid Sultan ; Warywoba, Daudi ; Ren, Fan ; Haque, Aman ; Pearton, S. J. ( September 2022 , Journal of Vacuum Science & Technology A)

   Focused Ga + ion milling of lightly Si-doped, n-type Ga 2 O 3 was performed with 2–30 kV ions at normal incidence and beam currents that were a function of beam voltage, 65 nA for 30 kV, 26 nA for 10 kV, 13 nA for 5 kV, and 7.1 nA for 2 kV, to keep the milling depth constant at 100 nm. Approximate milling rates were 15, 6, 2.75, and 1.5  μm 3 /s for 30, 10, 5, and 2 kV, respectively. The electrical effects of the ion damage were characterized by Schottky barrier height and diode ideality factor on vertical rectifier structures comprising 10  μm epitaxial n-Ga 2 O 3 on n + Ga 2 O 3 substrates, while the structural damage was imaged by transmission electron microscopy. The reverse bias leakage was largely unaffected even by milling at 30 kV beam energy, while the forward current-voltage characteristics showed significant deterioration at 5 kV, with an increase in the ideality factor from 1.25 to 2.25. The I–V characteristics no longer showed rectification for the 30 kV condition. Subsequent annealing up to 400 °C produced substantial recovery of the I–V characteristics for all beam energies and was sufficient to restore the initial ideality factor completely for beam energies up to 5 kV. Even the 30 kV-exposed rectifiers showed a recovery of the ideality factor to 1.8. The surface morphology of the ion-milled Ga 2 O 3 was smooth even at 30 kV ion energy, with no evidence for preferential sputtering of the oxygen. The surface region was not amorphized by extended ion milling (35 min) at 5 kV with the samples held at 25 °C, as determined by electron diffraction patterns, and significant recovery of the lattice order was observed after annealing at 400 °C. 

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5. Surface Adsorption and Air Damping Behavior of β‐Ga 2 O 3 Nanomechanical Resonators

   https://doi.org/10.1002/admt.202301356  

   Sui, Wen ; Enamul Hoque Yousuf, S. M. ; Liu, Yuncong ; Pearton, Stephen J. ; Feng, Philip X. ‐L. ( January 2024 , Advanced Materials Technologies)

   Beta gallium oxide (β‐Ga₂O₃) has emerged as a highly promising semiconductor material with an ultrawide bandgap ranging from 4.5 to 4.9 eV for future applications in power electronics, optoelectronics, as well as gas and ultraviolet (UV) radiation sensors. Here, surface adsorption and air damping behavior of doubly clamped β‐Ga₂O₃nanomechanical resonators are probed and systemically studied by measuring the resonance characteristics under different gas and pressure conditions. High responsivities of resonance to pressure are obtained by heating the devices up to 300 °C to induce an accelerated adsorption–desorption process. The initial surface conditions of the β‐Ga₂O₃thin film play important roles in affecting the resonant behavior. UV ozone treatment proves effective in altering the initial surface conditions of β‐Ga₂O₃nanosheets by eliminating physisorbed contaminants and filling oxygen vacancy defects residing on the surface, resulting in a consequential and discernible modification of the resonance behavior of β‐Ga₂O₃nanomechanical resonators. The surface adsorption and desorption processes in β‐Ga₂O₃demonstrate clear reversibility by exposing the UV treated β‐Ga₂O₃to air. This study attains first‐hand information on how the surface conditions of β‐Ga₂O₃affect its mechanical properties, and helps guide future development of transducers via β‐Ga₂O₃nanoelectromechanical systems (NEMS) for pressure sensing applications, especially in harsh environments.

    

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