Band Alignment and Enhanced Interfacial Conductivity Manipulated by Polarization in a Surfactant-Mediated Grown κ-Ga₂O₃/In₂O₃ Heterostructure

Abstract

Integration of intriguing ferroelectric κ-Ga2O3 on other oxide semiconductors opens an exciting avenue to invoke emergent transport phenomena and enable rational design of advanced device architectures, whereas the fundamental growth dynamics and physical properties of metastable κ-Ga2O3 are still far unexplored. In this work, we report on the heterostructure construction of single crystalline metastable orthorhombic κ-Ga2O3 epilayers and cubic In2O3(111) by means of laser molecular beam epitaxy. Elements of Sn and In are found to segregate to the growth surface and serve as surfactants to reduce the total surface energy and diffusion barrier of oxygen adatoms, hence producing Ga-rich conditions on the growth front, which in turn facilitates the stabilization of κ-phase Ga2O3. Depth-profiled X-ray photoemission spectral (XPS) analysis identified a type-I band alignment with a conduction band offset (CBO) of 0.45 eV and a valence band offset (VBO) of −1.15 eV for a κ-Ga2O3/In2O3 heterostructure. Determined by the analysis of Hall results with a double-layer model, a two-dimensional electron gas (2DEG) with a sheet carrier concentration of 1.2 × 1014 cm–2 and an enhanced mobility of 192 cm2/(V s) is confined at the heterostructure interface. The self-consistent Poisson–Schrödinger calculations indicate that the enhanced interfacial conductivity is a result of the combination of polarization manipulation and band discontinuity, well-supported by the characteristics of piezoelectric force microscopy and depth-profiled XPS. Integrating κ-Ga2O3 on other hexagonal polar semiconductors may open a possibility to manipulate the interfacial conductivity through polarization engineering and deliver advanced devices with multiple functionalities.

Comprehensive Raman study of orthorhombic κ/ε-Ga2O3 and the impact of rotational domains

“…The κ phase was found to thermally transition to β only under annealing at high temperatures T > 700 − 800 • C, 14,35 allowing for applications in devices requiring sufficiently high working temperatures. To date, the orthorhombic phase has been grown successfully 36 on a number of different substrates, including Al 2 O 3 (0001), GaN (0001), AlN (0001), 6H-SiC or β -Ga 2 O 3 (201), using halide vapour phase epitaxy, 14,37,38 atomic layer deposition, 39 metal-organic chemical vapor deposition, 15,18,22,27,30,35,37,[39][40][41][42][43][44] metal-organic vapor phase epitaxy, 1,[45][46][47][48] mist CVD 16,17,32,33,49,50 , plasma-assisted molecular beam epitaxy 51,52 , laser molecular beam epitaxy, 21,53 and pulsed laser deposition 12,13,24,[54][55][56][57] .…”

Growth of α-Ga2O3 on α-Al2O3 by conventional molecular-beam epitaxy and metal–oxide-catalyzed epitaxy

“…19) This growth mode has been observed for β-(Al,Ga) 2 O 3 on different substrates and surface orientations, as well as for different epitaxial growth techniques. [20][21][22][23][24] Many benefits arise from using MOCATAXY during the growth of Ga 2 O 3 . For example: (i) it can improve the surface morphologies of β-Ga 2 O 3 -based films.…”

Growth of $α-Ga_2O_3$ on $Al_2O_3$ by conventional molecular-beam epitaxy and metal-oxide-catalyzed epitaxy

“…In) is introduced to the growth system and results in metal-exchange catalysis [18]. This growth mode has been observed for β-(Al,Ga) 2 O 3 on different substrates and surface orientations, as well as for different epitaxial growth techniques [19][20][21][22][23]. Many benefits arise from using MOCATAXY during the growth of Ga 2 O 3 .…”

“…in highly metal-rich regimes) which can be beneficial for the suppression of undesired point (such as 𝑉 Ga ) defects in Ga 2 O 3 [12,13,18]. (iii) The formation of thermodynamically unstable Ga 2 O 3 phases becomes energetically favorable [16,18,23], e.g., the formation of the ϵ/κ-phase of Ga 2 O 3 , which has enabled novel ϵ/κ-Ga 2 O 3 -based heterostructures [22]. (iv) The growth rate (𝛤), possible growth temperatures (𝑇 G ), and crystalline quality of β-(Al,Ga) 2 O 3 -based thin films can be vastly enhanced [17].…”