In this work, an AlGaN-based Deep-Ultraviolet Light-Emitting Diode structure has been designed and simulated for the zincblende and wurtzite approaches, where the polarization effect is included. DFT analysis was performed to determine the band gap direct-to-indirect cross-point limit, AlN carrier mobility, and activation energies for p-type dopants. The multiple quantum wells analysis describes the emission in the deep-ultraviolet range without exceeding the direct-to-indirect bandgap cross-point limit of around 77% of Al content. Moreover, the quantum-confined Stark effect on wavefunctions overlapping has been studied, where Al-graded quantum wells reduce it. Both zincblende and wurtzite have improved electrical and optical characteristics by including a thin AlGaN with low Al content. Mg and Be acceptor activation energies have been calculated at 260 meV and 380 meV for Be and Mg acceptor energy, respectively. The device series resistance has been decreased by using Be instead of Mg as the p-type dopant from 3 kΩ to 0.7 kΩ.

We investigate the phase transitions and the properties of the topological insulator in InGaN/GaN and InN/InGaN double quantum wells grown along the [0001] direction. We apply a realistic model based on the nonlinear theory of elasticity and piezoelectricity and the eight-band k·p method with relativistic and nonrelativistic linear-wave-vector terms. In this approach, the effective spin–orbit interaction in InN is negative, which represents the worst-case scenario for obtaining the topological insulator in InGaN-based structures. Despite this rigorous assumption, we demonstrate that the topological insulator can occur in InGaN/GaN and InN/InGaN double quantum wells when the widths of individual quantum wells are two and three monolayers (MLs), and three and three MLs. In these structures, when the interwell barrier is sufficiently thin, we can observe the topological phase transition from the normal insulator to the topological insulator via the Weyl semimetal, and the nontopological phase transition from the topological insulator to the nonlocal topological semimetal. We find that in InGaN/GaN double quantum wells, the bulk energy gap in the topological insulator phase is much smaller for the structures with both quantum well widths of 3 MLs than in the case when the quantum well widths are two and three MLs, whereas in InN/InGaN double quantum wells, the opposite is true. In InN/InGaN structures with both quantum wells being three MLs and a two ML interwell barrier, the bulk energy gap for the topological insulator can reach about $1.2 \mathrm{meV}$. We also show that the topological insulator phase rapidly deteriorates with increasing width of the interwell barrier due to a decrease in the bulk energy gap and reduction in the window of In content between the normal insulator and the nonlocal topological semimetal. For InN/InGaN double quantum wells with the width of the interwell barrier above five or six MLs, the topological insulator phase does not appear. In these structures, we find two novel phase transitions, namely the nontopological phase transition from the normal insulator to the nonlocal normal semimetal and the topological phase transition from the nonlocal normal semimetal to the nonlocal topological semimetal via the buried Weyl semimetal. These results can guide future investigations towards achieving a topological insulator in InGaN-based nanostructures.