Polarization-Induced Band Inversion in In-Rich InGaN/GaN Quantum Wells

Łepkowski, S. P.; Bardyszewski, W.; Rodak, D.

doi:10.12693/aphyspola.126.1154

Cited by 1 publication

(3 citation statements)

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“…We would like to note that due to the negative SOI of InN, the highest light-hole (LH) sub-band with the

symmetry is above the highest heavy-hole (HH) sub-band with the

symmetry [ 13 ]. The names of the subbands reflect the dominant contribution of the CB, HH, and LH states around

[ 19 ]. As the value of x increases, the energy gap of In x Ga 1−x N alloys decreases toward the bandgap of InN and, more importantly, the built-in electric field in the QWs increases, causing an inversion of the CB and LH sub-bands and the TPT from the NI to the TI (see Figure 2 d).…”

Section: Resultsmentioning

confidence: 99%

“…= 0 [19]. As the value of x increases, the energy gap of In x Ga 1−x N alloys decreases toward the bandgap of InN and, more importantly, the built-in electric field in the QWs increases, causing an inversion of the CB and LH sub-bands and the TPT from the NI to the TI (see Figure 2d).…”

Section: In X Ga 1−x N/gan Dqwsmentioning

confidence: 98%

“…Unfortunately, the problem is that to achieve the TPT in InN/GaN QWs, the QW width should be at least four monolayers ( MLs ) and the growth of such thick and fully strained structures is extremely difficult, due to large strain reaching 11%. This problem can be partially overcome by applying InGaN alloys [ 13 , 19 , 20 ]. However, in In x Ga 1−x N/GaN QWs, the critical thickness for obtaining the TI state increases faster with decreasing In content in the QWs than the critical thickness for pseudomorphic growth [ 13 , 20 ].…”

Section: Introductionmentioning

confidence: 99%

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Polarization-Induced Phase Transitions in Ultra-Thin InGaN-Based Double Quantum Wells

Łepkowski

Anwar

2022

Nanomaterials

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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 . 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.

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“…We would like to note that due to the negative SOI of InN, the highest light-hole (LH) sub-band with the

symmetry is above the highest heavy-hole (HH) sub-band with the

symmetry [ 13 ]. The names of the subbands reflect the dominant contribution of the CB, HH, and LH states around

Section: Resultsmentioning

confidence: 99%

Section: In X Ga 1−x N/gan Dqwsmentioning

confidence: 98%