Heteroepitaxy of Ga_2(1‑x)In_2xO₃ layers by MOVPE with two different oxygen sources

Abstract

Ga 2(1-x) In 2x O 3 epitaxial layers have been grown on (0001) Al 2 O 3 substrates by metal organic vapour phase epitaxy (MOVPE). The process parameters were optimized and the effects related to the use of two alternative oxygenation sources like O 2 and H 2 O were studied. Different In content x [x = In/(In + Ga)] were investigated in order to determine the In solubility limit in β-Ga 2 O 3 . By using pure O 2 during the growth, the In amount detected in the layers increased linearly with the flux of In precursor injected into the reactor, but the X-ray diffraction patterns showed the presence of In 2 O 3 , in addition to β-Ga 2 O 3 , for every In content. The second phase formation was confirmed by a double step feature placed at the absorption edge in optical transmission spectra, compatible with the presence of the two materials. With H 2 O as an oxygenation source, no In 2 O 3 phase was observed up to xß0.25. The growth of the mixed Ga 2(1-x) In 2x O 3 phase was confirmed by XRD spectra, wherein the β-Ga 2 O 3 -related peaks shifted at lower 2θ angles as expected from the substitution of Ga 3+ ions with bigger In 3+ ones. The variation of bandgap was confirmed by optical transmittance measurements, which showed a red shift of the absorption edge corresponding to In incorporation.

(InxGa1−x)2O3alloys for transparent electronics

“…It is therefore unclear which structure the alloys would assume, and how this would affect stability and electronic properties. A number of papers have reported on the synthesis of such alloys [14][15][16][17][18][19][20][21][22][23][24][25] and on their crystal structure, band gaps and solubility limits. However, no consistent explanation for the experimental observations exists.…”

Ga2O3polymorphs: tailoring the epitaxial growth conditions

“…So far, most attention was concentrated on the thermodynamically stable b-Ga 2 O 3 phase, essentially for one reason: it can be grown both as a single crystal and as a thin epitaxial layer, thus enabling homoepitaxy and permitting one to lower the density of structural defects. Alloys with Al or In can modulate the b-Ga 2 O 3 bandgap, 4,5 allowing for the realization of heterostructures and the formation of a modulation doped 2D electron gas (2DEG) at the heterojunction, enabling high performance electronics. However, this phase presents also evident drawbacks, essentially due to the highly-asymmetric monoclinic structure.…”

Indium incorporation in homoepitaxial β-Ga2O3 thin films grown by metal organic vapor phase epitaxy

“…At low pressures (5-20 mbar), no indium was incorporated in the layers, even at very high flows of In precursor, while at a higher pressure of 100 mbar, indium was incorporated into the layers. 2,23 To study the amount of indium that could be incorporated into β-Ga 2 O 3 thin films using TEGa and TEIn precursors, all growth parameters are kept constant except for the indium flow rate varying from 0 to 0.26 μmol/min (growth temperature 825°C and chamber pressure 5 mbar). Figure 5 shows the surface morphology of the β-(In,Ga) 2 O 3 films (0, 0.09, and 0.26 μmol/min, as a representative) measured by atomic force microscopy.…”

“…They have applications in power devices and deep UV optoelectronic devices because of their novel properties such as distinctive electrical conductivity, large breakdown voltage, and high dielectric constant. [1][2][3][4][5] To fully exhaust their potential, the formation of (Ga 1−x In x ) 2 O 3 alloys is desired to tune the bandgap and for the development of heterostructures. However, β-Ga 2 O 3 exhibits a monoclinic crystal structure with the space group C2/m and lattice parameters of a = 12.214 Å, b = 3.0371 Å, c = 5.7981 Å and a monoclinic angle of β = 103.83°, 6 whereas In 2 O 3 represents a cubic bixbyite system with the space group Ia-3 and a lattice parameter of a = 10.117 Å.…”

“…Wang et al 12 reported the growth of polycrystalline (Ga 1−x In x ) 2 O 3 films with a homogenously Ga-substituted cubic In 2 O 3 microstructure up to 55% using volatile metal organic precursors In(dpm) 3 and Ga (dpm) 3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato), without the presence of a monoclinic (Ga x In 1−x ) 2 O 3 phase in the whole composition range 0 < x < 1. Recently, Baldini et al 2 reported that no In 2 O 3 phase was observed up to x = 0.15 during the growth of β-(Ga 1−x In x ) 2 O 3 on c-plane oriented sapphire substrates using trimethylgallium (TMGa) and trimethylindium (TMIn) precursors by metal organic vapor phase epitaxy (MOVPE). It is clear that the solubility limit of indium incorporation in β-Ga 2 O 3 is dependent on the growth method, the type of the substrate, and the nature of the precursor.…”