TY - JOUR
T1 - Universality of optical absorptance quantization in two-dimensional group-IV, III-V, II-VI, and IV-VI semiconductors
AU - Lannoo, Michel
AU - Prins, P. Tim
AU - Hens, Zeger
AU - Vanmaekelbergh, Daniel
AU - Delerue, Christophe
N1 - Publisher Copyright:
© 2022 American Physical Society.
PY - 2022/1/19
Y1 - 2022/1/19
N2 - The optical absorptance of a single graphene layer over a wide range of wavelengths is known to be remarkably constant at the universal value πα where α is the fine structure constant. Using atomistic tight-binding calculations, we show that the absorptance spectra of nanometer-thin layers (quantum wells) of group-IV, III-V, II-VI, or IV-VI semiconductors are characterized by marked plateaus at integer values of πα, in the absence of excitonic effects. In the case of InAs, the results obtained are in excellent agreement with the currently available experimental data. By revisiting experimental data on semiconductor superlattices, we show that πα is also a metric of their absorption when normalized to a single period. We conclude that the πα quantization is universal in semiconductor quantum wells provided that excitonic effects are weak and is therefore not specific to the zero-gap graphene case. The physical origin of this universality and its limits are discussed using analytical models that capture the main underlying physics of the lowest optical transitions in III-V and II-VI semiconductor quantum wells. These models show that the absorptance is ruled by πα independent of the material characteristics because of the presence of a dominant term in the Hamiltonian, linear in the wave vector k(∼V·k), which couples the conduction band to the valence bands. However, the prefactor in front of πα is not unity as in graphene due to the different nature of the electronic states. In particular, the spin-orbit coupling plays an important role in bringing the absorptance plateaus closer to integer values of πα. The case of IV-VI semiconductor (PbSe) quantum wells characterized by a rocksalt lattice and multivalley physics is very similar to that of graphene, with the specification that a "massful gap"is formed around the Dirac points.
AB - The optical absorptance of a single graphene layer over a wide range of wavelengths is known to be remarkably constant at the universal value πα where α is the fine structure constant. Using atomistic tight-binding calculations, we show that the absorptance spectra of nanometer-thin layers (quantum wells) of group-IV, III-V, II-VI, or IV-VI semiconductors are characterized by marked plateaus at integer values of πα, in the absence of excitonic effects. In the case of InAs, the results obtained are in excellent agreement with the currently available experimental data. By revisiting experimental data on semiconductor superlattices, we show that πα is also a metric of their absorption when normalized to a single period. We conclude that the πα quantization is universal in semiconductor quantum wells provided that excitonic effects are weak and is therefore not specific to the zero-gap graphene case. The physical origin of this universality and its limits are discussed using analytical models that capture the main underlying physics of the lowest optical transitions in III-V and II-VI semiconductor quantum wells. These models show that the absorptance is ruled by πα independent of the material characteristics because of the presence of a dominant term in the Hamiltonian, linear in the wave vector k(∼V·k), which couples the conduction band to the valence bands. However, the prefactor in front of πα is not unity as in graphene due to the different nature of the electronic states. In particular, the spin-orbit coupling plays an important role in bringing the absorptance plateaus closer to integer values of πα. The case of IV-VI semiconductor (PbSe) quantum wells characterized by a rocksalt lattice and multivalley physics is very similar to that of graphene, with the specification that a "massful gap"is formed around the Dirac points.
UR - http://www.scopus.com/inward/record.url?scp=85123774846&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.105.035421
DO - 10.1103/PhysRevB.105.035421
M3 - Article
AN - SCOPUS:85123774846
SN - 2469-9950
VL - 105
JO - Physical Review B
JF - Physical Review B
IS - 3
M1 - 035421
ER -