Planar and three-dimensional damage-free etching of β-Ga2O3 using atomic gallium flux

Abstract

In-situ etching using Ga flux in an ultra-high vacuum environment like MBE is introduced as a method to make high aspect ratio 3 dimensional structures in 𝛽-Ga2O3. Etching of 𝛽-Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of growth rate. In this study, we use this well-known reaction from epitaxial growth to intentionally etch 𝛽-Ga2O3. We demonstrate etch rate ranging from 2.9 nm/min to 30 nm/min with the highest reported etch rate being only limited by the highest Ga flux used. Patterned in-situ etching is also demonstrated and used to study the effect of fin orientation on the sidewall profiles and dopant (Si) segregation on the etched surface. Using in-situ Ga etching, we also demonstrate 150 nm wide fins and 200 nm wide nano pillars with high aspect ratio. This new etching method could enable future development of highly scaled vertical and lateral 3D devices in 𝛽-Ga2O3.The ultra-wide band gap semiconductor, 𝛽-Ga2O3 has attracted a lot of interest owing to its large breakdown field strength of 8 MV/cm 1-3 . When compared to existing state of the art technologies like Si, SiC and GaN, the high breakdown field strength theoretically predicts better performance for 𝛽-Ga2O3 based devices especially for applications like high voltage switching and high frequency power amplification 3 . In addition, the availability of bulk substrates grown from melt based techniques 4-7 and the wide range of controllable doping (10 15 cm -3 to 10 20 cm -3 ) 8,9 has led to rapid development of 𝛽-Ga2O3 devices in both vertical and lateral topology with excellent performance [10][11][12][13] .Due to the lack of p-type doping, most vertical devices in 𝛽-Ga2O3 require confined and scaled regions that control the flow of current between the source and drain, like vertical fins and pillars 10,14 . Using vertical fin structures also improves the electric field distribution in vertical Schottky barrier diodes by reducing the electric field seen at the Schottky metal semiconductor interface 15,16 . In addition, moving to a fin geometry would also result in increased power density and possibly enhancement-mode operation in lateral devices. Fabrication of these 3-dimensional structures require controlled, damage free etching that ideally provides vertical sidewalls (90 o

Plasma-free dry etching of (001) β-Ga2O3 substrates by HCl gas

“…42 However, plasma-free anisotropic etching approaches have been explored to produce plasma-damage-free high-aspect-ratio structures. So far, various etching techniques, such as hot phosphoric acid etching, 44,45 metal-assisted chemical etching (MacEtch), 46,47 atomic gallium flux etching in an ultra-high vacuum environment, 48 and hydrogen environment anisotropic thermal etching (HEATE), 49 have been reported, where the strong anisotropic nature of the b-Ga 2 O 3 crystal structure is more or less reflected in the etched structures. In terms of MacEtch, damage-free multiple fin channels were produced, and nearly zero-hysteresis operation of the FinFET was demonstrated.…”

Homoepitaxial growth of 1ˉ02 β-Ga2O3 by halide vapor phase epitaxy

“…This plasma damage causes an increase in the onresistance of MOSSBDs [26], a reduction in their effective channel mobility [27], and the occurrence of a large hysteresis loop in FinFETs [22]. As a result, plasma-free microfabrication techniques have been investigated [28][29][30][31][32][33]. Recently, plasma-free fabrication of the trench/fin structures by selective area growth or using a HCl gas etching technique has been reported [32,33].…”

High temperature stability of regrown and alloyed Ohmic contacts to AlGaN/GaN heterostructure up to 500 °C

“…Prior to regrowth, the sample was exposed to multiple cycles of Ga flux to remove any native suboxides from the GaN surface. 30 The angle of the regrown trench is approximately 58 as was measured through transmission electron microscopy images of the samples after the regrowth. On samples with regrown contacts, two types of TLMs were fabricated.…”