Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors

Abstract

The electronic and optical properties of (In x Ga1–x )2O3 alloys are highly tunable, giving rise to a myriad of applications including transparent conductors, transparent electronics, and solar-blind ultraviolet photodetectors. Here, we investigate these properties for a high quality pulsed laser deposited film which possesses a lateral cation composition gradient (0.01 ≤ x ≤ 0.82) and three crystallographic phases (monoclinic, hexagonal, and bixbyite). The optical gaps over this composition range are determined, and only a weak optical gap bowing is found (b = 0.36 eV). The valence band edge evolution along with the change in the fundamental band gap over the composition gradient enables the surface space-charge properties to be probed. This is an important property when considering metal contact formation and heterojunctions for devices. A transition from surface electron accumulation to depletion occurs at x ∼ 0.35 as the film goes from the bixbyite In2O3 phase to the monoclinic β-Ga2O3 phase. The electronic structure of the different phases is investigated by using density functional theory calculations and compared to the valence band X-ray photoemission spectra. Finally, the properties of these alloys, such as the n-type dopability of In2O3 and use of Ga2O3 as a solar-blind UV detector, are understood with respect to other common-cation compound semiconductors in terms of simple chemical trends of the band edge positions and the hydrostatic volume deformation potential.

Bandgap widening and behavior of Raman-active phonon modes of cubic single-crystalline (In,Ga)$_2$O$_3$ alloy films

“…5 In addition, other experimental studies could show an increase in optical absorption onset, with increasing Ga content, though the step size in varying the cation ratio Ga/(Ga+In) were rather coarse. 10,11,14,22,23 It has to be considered, that studying nanowires 20 or sintered ceramics 18 make the determination of bulk properties difficult. In this respect, high-quality single-crystalline films are much better suited, particularly in the regime of low Ga content, which is most controversially discussed.…”

(InxGa1−x)2O3 Thin Film Based Solar‐Blind Deep UV Photodetectors with Ultra‐High Detectivity and On/Off Current Ratio

“…This is consistent with recent result on the electronic structure of (In x Ga 1− x ) 2 O 3 alloys using density functional calculation by Swallow et al, which show higher density of state of In 4 d in In 2 O 3 than that of Ga 3 d in Ga 2 O 3 . [ 39 ] Herein, the increased density of state at the VB induced by In results in stronger optical absorption in (In 0.1 Ga 0.9 ) 2 O 3 . Therefore, the corresponding PDs would generate larger density of photoexcited carriers when illuminated by deep UV light.…”

Efficient Oxygen‐Vacancy Suppression and Electrical Stabilization of Solution‐Processed In2O3:Q (Q = S, Se) Thin‐Film Transistor with Chalcogen Alloying

“…The estimated values of m e * from four thin‐films are summarized in Figure 1b. We regard the average m e * of IGO to be 0.28 based on previously reported studies [ 19 ] and estimate the average m e * of In 2 O 3 and In 2 O 3 :Q (Q = S or Se) by a DFT calculation as 0.175 (In 2 O 3 ), 0.177 (Q = S), and 0.172 (Q = Se), respectively. This result is in good agreement with the values reported experimentally.…”