Optical properties of InGaN thin films in the entire composition range

Abstract

The optical properties of thick InGaN epilayers, with compositions spanning the entire ternary range, are studied in detail. High structural quality, single phase InxGa1-xN (0001) films were grown heteroepitaxially by radio-frequency plasma assisted molecular-beam epitaxy on freestanding GaN substrates. Their emission characteristics were investigated by low temperature photoluminescence spectroscopy, whereas variable angle spectroscopic ellipsometry was applied to determine the complex dielectric function of the films, in the 0.55–4.0 eV photon range. Photoluminescence lines were intense and narrow, in the range of 100 meV for Ga-rich InGaN films (x < 0.3), around 150 meV for mid-range composition films (0.3 < x < 0.6), and in the range of 50 meV for In-rich alloys (x > 0.6). The composition dependence of the strain-free emission energy was expressed by a bowing parameter of b = 2.70 ± 0.12 eV. The films' optical dielectric function dispersion was obtained by the analysis of the ellipsometric data employing a Kramers-Kronig consistent parameterized optical model. The refractive index dispersion was obtained for alloys in the entire composition range, and the corresponding values at the band edge show a parabolic dependence on the InN mole fraction expressed by a bowing parameter of b = 0.81 ± 0.04. The bowing parameter describing the fundamental energy bandgap was deduced to be equal to 1.66 ± 0.07 eV, consistent with the ab initio calculations for statistically random (non-clustered) InGaN alloys.

Absorption in ultrathin GaN-based membranes: The role of standing wave effects

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Analysis of the performance of InxGa1−xN based solar cells

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“…The In x Ga 1−x N has been considered a material with great potential to achieve high efficiency in tandem solar cells because the energy gap (Eg) can be varied from 0.7 to 3.4 eV [1]. However, even after nearly 20 years of research and significant incremental contributions, only a few reports have shown a small efficiency improvement [2][3][4]. Some reasons for this are the following technological challenges:…”

Improved GaN Quantum Well Microcavities for Robust Room Temperature Polaritonics

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