Faceting and metal-exchange catalysis in (010) β-Ga2O3 thin films homoepitaxially grown by plasma-assisted molecular beam epitaxy

Abstract

We here present an experimental study on (010)-oriented β-Ga2O3 thin films homoepitaxially grown by plasma assisted molecular beam epitaxy. We study the effect of substrate treatments (i.e., O-plasma and Ga-etching) and several deposition parameters (i.e., growth temperature and metal-to-oxygen flux ratio) on the resulting Ga2O3 surface morphology and growth rate. In situ and ex-situ characterizations identified the formation of (110) and (1¯10)-facets on the nominally oriented (010) surface induced by the Ga-etching of the substrate and by several growth conditions, suggesting (110) to be a stable (yet unexplored) substrate orientation. Moreover, we demonstrate how metal-exchange catalysis enabled by an additional In-flux significantly increases the growth rate (>threefold increment) of monoclinic Ga2O3 at high growth temperatures, while maintaining a low surface roughness (rms < 0.5 nm) and preventing the incorporation of In into the deposited layer. This study gives important indications for obtaining device-quality thin films and opens up the possibility to enhance the growth rate in β-Ga2O3 homoepitaxy on different surfaces [e.g., (100) and (001)] via molecular beam epitaxy.

Isotopic study of Raman active phonon modes in β-Ga2O3

“…The MEXCAT deposition process 33,91,98 allows to widen the deposition window of Ga 2 O 3 to otherwise forbidden growth regimes (e.g. the high T g and metal-to-oxygen flux ratios used in this work), while at the same time allowing for low incorporation of the catalyzing element.…”

“…Fig. S1b) 91,98 . Indeed the correct probe of the (201) planes was experimentally verified via Raman spectroscopy which highlighted the mode intensity ratios expected for the (201) planes (Fig.…”

“…A β − Ga 2 O 3 layer was homoepitaxially deposited (deposition time 445 min) on top of an unintentionally doped (010)-oriented substrate with In-mediated metal-exchange catalysis (MEXCAT) [89][90][91] in an MBE chamber equipped with an oxygen-plasma source run at a power of 300 W. For this deposition run, nominally 97.39% isotopically enriched 18 O 2 was employed to provide an oxygen flux of 0.38 standard cubic centimeter per minute (sccm) during the layer growth. For gallium (with natural isotopic abundance) a beam equivalent pressure (BEP) of BEP Ga = 1.27 • 10 −7 mbar was used (equivalent to a particle flux of Φ Ga = 2.2 nm −2 s −1 ), while the additional In-flux necessary to allow the catalytic growth of the layer at a substrate temperature of T g = 900 • C was set to…”

Ga2O3polymorphs: tailoring the epitaxial growth conditions

“…e-Ga 2 O 3 layers in the presence of the catalysing element Sn were also reported for PLD grown thin films on MgO(111), SrTiO 3 (111), and yttria-stabilized ZrO 2 (111) substrates. 70,79 Notably, MBE In-mediated metal-exchange catalysis has been also applied to widen the growth window of Ga 2 O 3 layers deposited on all the available b-Ga 2 O 3 bulk substrate orientations [i.e., (010), ( 100), (001), and (% 201)] 12,13,80 but differently from the discussed heteroepitaxial growth; in this case the deposited layers always preserved the monoclinic structure of the substrate.…”

Kinetic Monte Carlo model for homoepitaxial growth of Ga2O3

“…A variety of possible substrate orientations has been used, such as (100), (010), (001), and (201) [1,7,8]. Hitherto, step flow was only achieved on (100) surfaces [9][10][11][12], whereas on all surfaces with other orientations tried so far either faceted surfaces are forming [13] or a three-dimensional surface structure occurs, which does not reproduce the initial monoatomic stepped surface structure of the substrate.…”