Abstract
The III-Nitride digital alloy (DA) is comprehensively studied as a short-period superlattice nanostructure consisting of ultra-thin III-Nitride epitaxial layers. By stacking the ultra-thin III-Nitride epitaxial layers periodically, these nanostructures are expected to have comparable optoelectronic properties as the conventional III-Nitride alloys. Here we carried out numerical studies on the InGaN DA showing the tunable optoelectronic properties of the III-Nitride DA. Our study shows that the energy gap of the InGaN DA can be tuned from ~0.63 eV up to ~2.4 eV, where the thicknesses and the thickness ratio of each GaN and InN ultra-thin binary layers within the DA structure are the key factors for tuning bandgap. Correspondingly, the absorption spectra of the InGaN DA yield broad wavelength tunability which is comparable to that of bulk InGaN ternary alloy. In addition, our investigation also reveals that the electron-hole wavefunction overlaps are remarkably large in the InGaN DA structure despite the existence of strain effect and build-in polarization field. Our findings point out the potential of III-Nitride DA as an artificially engineered nanostructure for optoelectronic device applications.
Highlights
III-Nitride materials have been extensively studied and implemented in advancing the solid-state lighting technologies[1,2,3,4,5,6,7,8,9,10,11,12,13,14]
When the thicknesses of the GaN and InN layer increase from 1 ML to 4 MLs the inter-well resonant coupling effect within the superlattice is significantly suppressed, the bandwidths reduce from ~1.152 eV to ~0.116 eV for C-1 miniband, from ~0.449 eV to ~0.0001 eV for HH-1 miniband, and from ~0.451 eV to ~0.053 for the LH-1 miniband. These trends suggest that the miniband structures and optoelectronic properties of the digital alloy (DA) can be engineered by tuning the thickness of GaN and InN ultra-thin binary layers
The effective energy gap of the InGaN digital alloys can be tuned artificially by changing the thickness of each GaN and InN thin layers. These trends indicate that when the thicknesses of GaN barrier layer become much larger the inter-well resonant coupling effect will become negligible leading to the degeneration of the minibands into confined-states, the superlattice-based DA will become the conventional multiple quantum wells (MQWs)
Summary
The III-Nitride digital alloy (DA) is comprehensively studied as a short-period superlattice nanostructure consisting of ultra-thin III-Nitride epitaxial layers. We present a comprehensive analysis of the ultra-short period superlattice-based InN/GaN digital alloy (DA) structure as a potential alternative into the high crystalline quality In-rich InGaN material along with the tunable effective bandgap. The III-Nitride DA, InGaN DA in this work, is an artificial nano-structure based on short-period GaN/InN superlattice, which is formed by alternate epitaxy of ultra-thin layers of non-phase separated GaN and InN binary alloys. For better understanding of the optoelectronic properties of the InGaN DA structure, numerical calculations were carried out on a set of 50-period InGaN DA, in which the thickness of each GaN and InN binary layers is varied from 1 ML to 4 MLs. The band lineup of the InGaN DA was modeled based on a modified Kronig-Penney model, in which the strain effect induced by lattice mismatch and built-in polarization effect attributed to both spontaneous and piezoelectric polarization are considered[60,61,62,63]. The material parameters used in this study were obtained from previous literatures[23, 60, 61, 65]
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