Kevin Angello Lizarraga Olivares

@article{nokey,

title = {Thickness-dependent excitonic properties of hexagonal boron-nitride thin films},

author = {Nguyen Van Thanh and Nguyen Tuan Hung and Hikaru Takehara and Atsushi Taguchi and Hsin Yi and Pablo Solís-Fernández and Hiroki Ago and Pengfei Yang8 and Lain-Jong Li and Kevin Lizárraga and Riichiro Saito and Hsiang-Lin Liu

},

url = {https://journals.aps.org/prmaterials/abstract/10.1103/231t-g3mn},

doi = {10.1103/231t-g3mn},

year  = {2025},

date = {2025-07-25},

urldate = {2025-07-25},

journal = {Physical Review Materials},

abstract = {We report the excitonic properties of hexagonal boron-nitride (h-BN) thin films as a function of thickness using deep-ultraviolet photoluminescence spectroscopy and spectroscopic ellipsometry for optical absorption analysis. The peak positions of the defect-induced donor-acceptor PL emissions and the band-to-band exciton absorption exhibit a blueshift with increasing thickness or an increase in the effective dielectric constant of the surrounding environment. The optical absorption spectra analyzed using the Elliott model, combined with renormalized band-gap calculations, reveal an exciton binding energy of 1.04 eV for monolayer h-BN, which decreases to 0.16 eV in h-BN single crystal due to environmental screening effects on the electron-hole interactions. Furthermore, both the band-gap value and Urbach energy decrease as the film thickness increases. The optical absorption coefficient derived from spectroscopic ellipsometry measurement of monolayer h-BN is directly compared with results from the first-principles GW plus Bethe-Salpeter equation calculations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Crystalline environment of luminescent Tb3+ ions embedded in indium tin oxide thin films: A DFT and crystal field analysis assessment},

author = {E. Serquen and K. Lizárraga and L. A. Enrique and F. Bravo and S. Mishra and P. Llontop and P. Venezuela and L. R. Tessler and J. A. Guerra},

doi = {10.1103/PhysRevMaterials.9.055202},

year  = {2025},

date = {2025-05-27},

urldate = {2025-05-27},

journal = {Physical Review Materials},

volume = {9},

issue = {5},

pages = {055202},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Description of excitonic absorption using the Sommerfeld enhancement factor and band-fluctuations},

author = {K Lizárraga and E Serquen and P Llontop and L A Enrique and M Piñeiro and E Perez and A Tejada and F Ruske and L Korte and J A Guerra},

url = {https://iopscience.iop.org/article/10.1088/1361-6463/ad91c1},

doi = {10.1088/1361-6463/ad91c1},

year  = {2024},

date = {2024-11-26},

urldate = {2024-11-26},

journal = {Journal of Physics D: Applied Physics},

volume = {58},

number = {6},

abstract = {One of the challenges of excitonic materials is the accurate determination of the exciton binding energy and bandgap from optical measurements. The difficulty arises from the overlap of the discrete and continuous excitonic absorption at the band edge. Many researches have modeled the shape of the absorption edge of such materials on the seminal formulation proposed by Elliott in 1957 (Phys. Rev. 108 1384–9) and its several modifications such as non-parabolic bands, magnetic potentials and electron–hole-polaron interactions. However, exciton binding energies obtained from optical absorption often vary strongly depending on the chosen ‘Elliott formula’. Here, we propose an alternative and rather simple approach, which has previously been successful in the determination of the optical bandgap of amorphous, direct and indirect semiconductors, based on the band-fluctuations (BFs) model. In this model, the fluctuations due to disorder, temperature or lattice vibrations give rise to the well known exponential shape of band tail states. The formulation results in an analytic equation for the fundamental absorption with 6 parameters only. To test it, the binding energy and optical bandgap of GaAs and the family of tri-halide perovskites over a wide range of temperatures, are obtained by fitting the modified Elliott model. The results for the bandgap, linewidth and exciton binding energy are in good agreement with reports based on non-optical measurements. Moreover, due to the polar nature of perovskites, the retrieved binding energies can be compared with those computed with a model proposed by Kane (1978 Phys. Rev. B 18 6849). In the latter model, the exciton is surrounded by a cloud of virtual phonons interacting via the Frölich interaction. As a consequence, the upper bound for the binding energy of the exciton-polaron system can be estimated. These results are in good agreement with the optical parameters obtained with the proposed Elliott equation including BFs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {New optical dispersion models for the accurate description of the electrical permittivity in direct and indirect semiconductors},

author = {K Lizárraga and L A Enrique-Morán and A Tejada and M Piñeiro and P Llontop and E Serquen and E Perez and L Korte and J A Guerra},

url = {https://iopscience.iop.org/article/10.1088/1361-6463/acd859},

doi = {10.1088/1361-6463/acd859},

year  = {2023},

date = {2023-06-08},

urldate = {2023-06-08},

journal = {Journal of Physics D: Applied Physics},

volume = {56},

number = {36},

abstract = {We propose new optical dispersion models to describe the imaginary part of the electrical permittivity of dielectric and semiconductor materials in the fundamental absorption region. We work out our procedure based on the well-known structure of the semi-empirical Tauc–Lorentz dispersion model and the band-fluctuations approach to derive a five-parameter formula that describes the Urbach, Tauc and high-absorption regions of direct and indirect semiconductors. Main features of the dispersion models are the self-consistent generation of the exponential Urbach tail below the bandgap and the incorporation of the Lorentz oscillator behavior due to electronic transitions above the fundamental region. We apply and test these models on optical data of direct (MAPbI3, gallium arsenide and indium phosphide), indirect (gallium phosphide and crystalline silicon), and amorphous hydrogenated silicon semiconductors, accurately describing the spectra of the imaginary part of the electrical permittivity. Lastly, we compare our results with other similarly inspired dispersion models to assess the optical bandgap, Urbach tail and oscillator central resonance energy.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}