Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf Overlapping efects of the optical transitions of GaNAs thin flms grown by molecular beam epitaxy I.E. Cortes-Mestizo a, ⁎ , L.I. Espinosa-Vega b , J.A. Espinoza-Figueroa b , C.M. Yee-Rendón c , L. Zamora-Peredo d , A.G. Rodríguez b , C.A. Mercado-Ornelas b , F.E. Perea-Parrales b , V.H. Méndez-García b a CONACYT- Coordinación para la Innovación y la Aplicación de la Ciencia y la Tecnología (CIACYT), Universidad Autónoma de San Luis Potosí, Av. Sierra Leona #550, Col. Lomas 2a Sección, San Luís Potosí, San Luis Potosí, 78210, México b Coordinación para la Innovación y la Aplicación de la Ciencia y la Tecnología (CIACYT), Universidad Autónoma de San Luis Potosí, Av. Sierra Leona #550, Col. Lomas 2a Sección, San Luís Potosí, San Luis Potosí, 78210, México c Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Sinaloa, Av. de las Americas y Blvd. Universitarios, Culiacán, Sinaloa, 80000, México d Centro de Investigación en Micro y Nanotecnología, Universidad Veracruzana, Calzada Ruiz Cortínes #455, Boca del río, Veracruz, 94294, México ARTICLEINFO Keywords: Gallium arsenide nitride Conduction band splitting Photorefectance Ellipsometry Molecular beam epitaxy GaNAs/GaAs heterojunction Band anti-crossing model Dilute nitride ABSTRACT Photorefectance and ellipsometry are two very useful optical spectroscopy techniques employed to analyze the electronic band structure of semiconductors. Photorefectance and ellipsometry spectra of gallium arsenide ni- tride (GaNAs) thin flms on gallium arsenide (GaAs) layers may be composed of transitions from the conduction bands of the alloy and the binary (E -, E + , and E 0 , respectively) in conjunction with their interaction spin-orbit split-of valence band (E - +Δ 0 and E 0 +Δ 0 ). For low concentration of nitrogen (between 0.2 and 0.6 %), the determination of the E + conduction band becomes difcult to distinguish by the fact that critical points are superimposed in the spectrum of both characterization techniques. In this work, a method to determine the E + conduction band of GaNAs thin flms grown on GaAs by molecular beam epitaxy is proposed when the over- lapping of spectral features infuences their optical determination. When using spectroscopic characterization techniques, the modulation/excitation region depends on the wavelength employed and sample characteristics, and consequently low nitrogen concentration in the alloy in conjunction with the thickness of the GaNAs layers have been found responsible for the signal overlapping. It is demonstrated that by decreasing the sample tem- perature in the photorefectance process the overlapping is avoided, allowing for a correct interpretation of the GaNAs conduction band splitting analysis and discarding the contribution of built-in electric felds. From these results, we achieved a precise experimental determination of the presence/absence of the band splitting pre- dicted by the band anti-crossing model using non-destructive characterization tools. 1. Introduction Through the substitution of arsenic by nitrogen atoms in the gallium arsenide (GaAs) host lattice the gallium arsenide nitride (GaN x As 1-x , where x is the mole fraction of N) ternary compound is formed. This material has been widely researched due to the attractive large bandgap bowing observed even for small atomic percentage of nitrogen (%N) incorporation since it was experimentally demonstrated in the early 1990s [1]. For instance, within the diluted regime (%N < 3) the band gap energy is reduced by ~100 meV per %N [2]. On this way, the development of the GaNAs has been a subject of great interest due to the potential applications in optoelectronic devices, covering emission/ absorption processes between red to ultraviolet [3-6]. The behavior of the band structure of the GaNAs system is explained by the band anti-crossing model (BAC), which describes the role of nitrogen incorporation on a wide variety of III–N–V alloys. The BAC indicates that anti-crossing interaction between the electronic states of the localized nitrogen and energy states of the GaAs host matrix split the conduction band into two sub-bands labeled as E - and E + [7]. The band gap of the GaNAs system is related to E - while the E + level is an extra conduction-band edge of the GaNAs. Thus, the GaN x As 1-x bandgap can be tuned in by the %N used in the alloy, according to BAC. As it was mentioned earlier, a small increment of %N decreases the bandgap energy, E - , while at the same time increases the energy separation https://doi.org/10.1016/j.tsf.2020.137969 Received 12 September 2019; Received in revised form 7 February 2020; Accepted 18 March 2020 ⁎ Corresponding author. E-mail address: irving.cortes@uaslp.mx (I.E. Cortes-Mestizo). Thin Solid Films 702 (2020) 137969 Available online 20 March 2020 0040-6090/ © 2020 Elsevier B.V. All rights reserved. T