β-Ga 2 O 3 , with a bandgap of ∼4.6−4.9 eV and readily available bulk substrates, has attracted tremendous interest in the wide bandgap semiconductor community. Producing high aspect ratio β-Ga 2 O 3 3D nanostructures without surface damage is crucial for nextgeneration power electronics. However, most wet etching methods can only achieve very limited aspect ratios, while dry etch usually damages the surface due to high energy ions. In this work, we demonstrate the formation of β-Ga 2 O 3 fin arrays on a (010) β-Ga 2 O 3 substrate by metalassisted chemical etching (MacEtch) with high aspect ratio and sidewall surfaces with excellent quality. The etching was found to be strongly crystal orientation dependent, and three kinds of vertical structures were formed after MacEtch. The Schottky barrier height (SBH) between Pt and various MacEtch-produced β-Ga 2 O 3 surfaces and sidewalls was found to decrease as the aspect ratio of the β-Ga 2 O 3 vertical structure increased. This could be attributed to the different amount of oxygen lost at the surface after etching, as indicated by the XPS and TEM examination. Very little hysteresis was observed in the capacitance−voltage characteristics for the 3D Pt/Al 2 O 3 /β-Ga 2 O 3 MOS capacitor structures, and the extracted interface trap density was as small as 2.73 × 10 11 cm −2 eV −1 , comparable to or lower than that for unetched planar β-Ga 2 O 3 surfaces. KEYWORDS: β-Ga 2 O 3 , metal-assisted chemical etching, high aspect ratio, XPS, Schottky barrier height, D it β-Gallium oxide (β-Ga 2 O 3 ) is considered a promising material for high-power applications due to its ultrawide band gap of 4.6−4.9 eV, 1,2 high theoretical breakdown electric field of 8 MV/cm, and reasonable 150 cm 2 /V-s electron mobility. 3 These properties lead to a 1721 Baliga's figure of merit for the powering switch and outperforms the value of SiC and GaN. 4−6 Moreover, β-Ga 2 O 3 is a wide bandgap semiconducting material with the availability of single crystalline bulk substrate and controllable n-type doping concentration over the full range of <10 14 and up to >10 20 cm −3 . 7,8 Over the past five years, many high-power β-Ga 2 O 3 applications, such as Schottky diodes, 9,10 MESFETs, 11 MOSFETs, 12−15 vertical transistors, [16][17][18]19 have been successfully demonstrated. However, the β-Ga 2 O 3 transistors published so far still suffer from low current density compared to GaN devices. To further enhance the on-current and gate control, the development of techniques for fabricating β-Ga 2 O 3 vertical structures with high aspect ratios (ARs) and smooth surfaces is essential. 3D β-Ga 2 O 3 nanostructures will also be useful for solar-blind photodetectors and sensing applications. 20,21 Although inductively coupled plasma reactive ion etching (ICP-RIE) of β-Ga 2 O 3 has been recently studied with surface

Nanoscale groove textured β-Ga2O3 by room temperature inverse metal-assisted chemical etching and photodiodes with enhanced responsivity

In this work, β-Ga2O3 fin field-effect transistors (FinFETs) with metalorganic chemical vapor deposition grown epitaxial Si-doped channel layer on (010) semi-insulating β-Ga2O3 substrates are demonstrated. β-Ga2O3 fin channels with smooth sidewalls are produced by the plasma-free metal-assisted chemical etching (MacEtch) method. A specific on-resistance (Ron,sp) of 6.5 mΩ·cm2 and a 370 V breakdown voltage are achieved. In addition, these MacEtch-formed FinFETs demonstrate DC transfer characteristics with near zero (9.7 mV) hysteresis. The effect of channel orientation on threshold voltage, subthreshold swing, hysteresis, and breakdown voltages is also characterized. The FinFET with channel perpendicular to the [102] direction is found to exhibit the lowest subthreshold swing and hysteresis.

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Compound semiconductor heterojunctions have enabled various optoelectronic devices. Nonetheless, the formation of heterojunctions is limited by the lattice matching between the two materials. On the other hand, two-dimensional (2D) semiconducting material and three-dimensional (3D) material heterojunction has attracted tremendous attention in recent years due to its immunity to the lattice mismatch. However, 2D/3D heterojunction formation by transferring 2D material suffers from contamination and defects created during the transfer process. Thus, direct growth of 2D material on 3D semiconducting material is crucial for the next generation heterojunction devices. In this work, we demonstrate n-MoS 2 /p-GaN diodes monolithically formed by quasi-van der Waals epitaxy. Monolayer MoS 2 has been grown on a GaN substrate through a powder-based chemical vapor deposition (CVD) system. The triangular MoS 2 flakes show well-aligned morphology with the GaN hexagonal crystal structure in the initial stage of the growth. Raman and PL mapping confirms the excellent uniformity of the monolayer MoS 2 film on the GaN substrate. The growth of MoS 2 on patterned GaN substrates are also studied, which yields monolayer and few-layer MoS 2 formation on the planar surface and the pyramidal sidewalls, respectively. Finally, the n-MoS 2 / p-GaN diodes have been electrically characterized and show well-defined rectifying behavior with an ideality factor of ∼1.3.