Abstract
This paper focuses on the determination of the bandgap energy bowing parameter of strained and relaxed InxGa1−xN layers. Samples are grown by metal organic vapor phase epitaxy on GaN template substrate for indium compositions in the range of 0<x<0.25. The bangap emission energy is characterized by cathodoluminescence and the indium composition as well as the strain state are deduced from high resolution X-ray diffraction measurements. The experimental variation of the bangap emission energy with indium content can be described by the standard quadratic equation, fitted using a relative least square method and qualified with a chi square test. Our approach leads to values of the bandgap energy bowing parameter equal to 2.87±0.20eV and 1.32±0.28eV for relaxed and strained layers (determined for the first time since the revision of the InN bandgap energy in 2002), respectively. The corresponding modified Vegard’s laws describe accurately the indium content dependence of the bandgap emission energy in InGaN alloy and for the whole range of indium content. Finally, as an example of application, 3D mapping of indium content in a thick InGaN layer is deduced from bandgap energy measurements using cathodoluminescence and a corresponding hyperspectral map.
Highlights
The tunability of the fundamental bandgap of indium gallium nitride (InGaN) across the full visible range spectrum has led to the development of a variety of optoelectronic devices including blue, green, red and white light-emitting diodes [1], blue and green laser diodes [2, 3], and solar cells [4,5,6,7]
The composition dependence (x) of the bandgap can be generally described using a modified Vegard’s law including, in addition to the linear interpolation, a quadratic term depending on a bowing parameter b: ENInBGEaN = x × ENInBNE + (1 − x) × ENGBaNE − b × x × (1 − x) where ENGBaNE and ENInBNE are the values of the emission energy deduced from optical measurements
As shown by Parker et al [12] and Ponce et al [13] different dependencies of the bandgap emission energy with the indium composition are expected for InxGa1−xN layers according to their strain states
Summary
The tunability of the fundamental bandgap of indium gallium nitride (InGaN) across the full visible range spectrum has led to the development of a variety of optoelectronic devices including blue, green, red and white light-emitting diodes [1], blue and green laser diodes [2, 3], and solar cells [4,5,6,7]. As shown by Parker et al [12] and Ponce et al [13] different dependencies of the bandgap emission energy with the indium composition are expected for InxGa1−xN layers according to their strain states. High resolution X-ray diffraction (XRD) is used to determine the indium content as well as the strain state rate of the InGaN alloys layers. For both relaxed and strained InGaN layers, the experimental bandgap energy bowing parameters were fitted using a relative least square method from the compositional dependence of the emission bandgap, and qualified by a chi square test [17]. Results highlight the phase separation issue in such thick layers
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