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

Abstract

The influence of Ga incorporation into cubic In 2 O 3 on the electronic and vibrational properties is discussed for (In 1−𝑥 ,Ga 𝑥 ) 2 O 3 alloy films grown by molecular beam epitaxy. Using spectroscopic ellipsometry, a linear dependence of the absorption onset on the Ga content 𝑥 is found with a blueshift of up to 150 meV for 𝑥 = 0.1. Consistently, the fundamental band gap exhibits a blueshift as determined by hard X-ray photoelectron spectroscopy. The dependence of the absorption onset and the effective electron mass on the electron concentration is derived from the infrared dielectric functions for a Sn doped alloy film. The influence of alloying on phonon modes is analyzed on the basis of Raman spectroscopic measurements. The frequencies of several phonon modes are identified as sensitive measures for the spectroscopic determination of the Ga content.

Molecular beam epitaxy of single-crystalline bixbyite (In$_{1-x}$Ga$_x$)$_2$O$_3$ films ($x \leq 0.18$): Structural properties and consequences of compositional inhomogeneity

“…The observed blueshift of the absorption onset by 95 meV induced by alloying is somewhat lower than expected based on the results reported in Ref. 49, presumably due to the different growth conditions. Note that many-body corrections such as the Burstein-Moss effect and band gap renormalization can be neglected for the investigated sample, 35 which has been annealed in oxygen (rapid thermal annealing at a final temperature of 800 • C at atmospheric pressure for 60 s).…”

“…Figure 7 the frequency of such phonon modes for the samples of series II, which includes films with nominally x > 0.10, along with the data reported in Ref. 49. The Raman spectra of all alloy films exhibit a typical fingerprint of In 2 O 3 phonon modes with no indication of additional phases (as in the high quality bulk crystal in Ref.…”

“…Strikingly, the frequencies of all phonon modes remain constant for nominal Ga contents above x > 0.10, with the saturation values of the individual phonon frequencies agreeing reasonably well with those obtained for x = 0.10. 49 The absence of a further blueshift with increasing nominal Ga content is most likely related to the findings of the TEM investigations reporting a Ga incorporation of approximately x = 0.08 in the main "matrix" of the film and inclusions with significantly higher Ga content for those films. Apparently, the Raman spectra are dominated by scattering in the "matrix" of the films and not by the total Ga content of the films.…”

“…8. A comparison between the dielectric functions of the samples of series II and pure In 2 O 3 can be found in the recent work of Feldl et al 49 . The observed blueshift of the absorption onset by 95 meV induced by alloying is somewhat lower than expected based on the results reported in Ref.…”

“…Spectroscopic ellipsometry is demonstrated in Ref. 49 to be a further spectroscopic tool to study the incorporation of Ga in (In 1-x Ga x ) 2 O 3 alloy films. The onset of optical absorption has been shown to exhibit a pronounced blueshift with increasing Ga content for the samples of series III.…”