Pseudo-dielectric function spectra of the near surface layer of GaAs implanted with various fluence of Xe+ ions
Introduction
After the discovery of the transistor in 1947, gallium arsenide (GaAs) was assessed as a candidate material for electronic devices. GaAs has a direct energy band gap, which means that the transitions between the valence band and the conduction band require only a change in energy and no change in momentum. Hence, GaAs is considered to be a good optoelectronic material and is used extensively in light-emitting diodes and semiconductor lasers. At low electric fields, the electron mobility in intrinsic GaAs is 8500 cm2/Vs, which is approximately six times that of silicon [1,2]. This high mobility was the reason for much of the early research and development of GaAs Field Effect Transistors. Practically, GaAs is widely used in the advanced devices like the monolithic microwave integrated circuits, microwave frequency integrated circuits, infrared light emitting diodes, optical windows, laser diodes and most importantly in solar cells [[3], [4], [5]]. When compared with crystalline silicon solar cell, GaAs solar cells have some advantages such as high-efficiency potential, possibility to use of thin-films and good temperature coefficient.
Ion implantation is a well-established and widely used technology in the development of electronics and optoelectronics [6]. It is a technique for modifying the physical properties of near surface regions in various materials. This alteration, however, is accompanied by the formation of disordered subsurface layers. The concentration of defects is affected by ion energy, ion mass and ion fluence. The changes of the properties of GaAs implanted with different ions such as In+, Xe+, and Ba+ were discussed in [7] by G.F. Feng et al. and in [8] by Kulik et al. emphasizing the damage in the materials after the implantation. The thickness and composition of the disordered layers were investigated using the Rutherford backscattering spectroscopy in [7,8], while the optical properties and the complex dielectric function were measured by the spectroscopic ellipsometry (SE).
Ion implantation also influences the formation of native oxide layers on the surface of materials after the exposition to ambient air. The effect was observed for GaAs implanted with Ar+, Al+, and Xe+ ions. The thickness and chemical composition of the native oxide layers on the GaAs surface were discovered to be dependent on the implantation fluence [9,10].
In our previous study [10], the formation of native oxides on the surface of GaAs samples before and after ion implantation was investigated. The linear correlation between the surface atomic density of the native oxide layer and the ion fluence was demonstrated in the fluence range of 2 × 1013 to 8 × 1014 ions/cm2. However, as a remarkable effect, the surface atomic density of oxide in the ion fluence range from 1 × 1015 to 3 × 1016 ions/cm2 strongly increases due to a significant increase of the thickness of the layer. It was assumed that such almost step-like increase of thickness is caused by the amorphization of the implanted GaAs layer. The aim of the present work is to answer the question whether the ion implantation causes the changes in the properties of the subsurface GaAs layers as well as the native oxide layer. In order to answer the question, the GaAs samples were irradiated with 250-keV Xe+ ions at various fluence. The pseudo-dielectric function was investigated though SE measurement with rotating analyzer configuration. The depth profile of elements in GaAs samples were determined by the Rutherford backscattering spectrometry with nuclear reaction method (RBS/NR). The influence of noble gas Xe+ implantation with various fluence on near surface layers of GaAs is presented.
Section snippets
Materials and methods
A bromine methanol chemo-mechanical polishing technique was used to clean the surface of semi-insulating GaAs samples [11]. One of the processed samples was kept as a virgin sample while the others were irradiated with the Xe+ ions. The energy of Xe+ beam was 250 keV and the fluence ranged from 3 × 1012 up to 3 × 1016 ions/cm2, with the beam current on the target fixed at ∼1μA/cm2. The arc discharge ion source is used to generate the ion beam. The beam has a circular profile with a diameter of
Results and discussions
The ellipsometric angles spectra Ψ(E) and ∆(E) from both virgin and Xe+ implanted samples were acquired. It should be reminded here that is equal to the ratio of complex Fresnel reflection coefficients Rp/Rs for parallel and perpendicular polarizations of light beam [17,18]. Fig. 1 shows the relevant Ψ(E) and ∆(E) spectra recorded at different angles of incidence.
Two local maxima in the Ψ spectra for the photon energy near 3.0 eV are shown in Fig. 1a. According to the published data
Conclusion
The Xe+ ion implantation process changes the values of the ellipsometric angles and the spectral shapes of the pseudo-dielectric functions of the near surface GaAs layer. This change is related to the radiation-induced damage in the implanted layer and transition from crystalline to amorphous GaAs phase with the increasing 250-keV Xe+ ion fluence. The thickness of native oxide on implanted GaAs grows with the ion fluence as well. The study reveals that when the Xe+ fluence increase, the
CRediT authorship contribution statement
P.L. Tuan: Writing – original draft, Conceptualization, Methodology, Formal analysis, Software, Writing – review & editing. M. Kulik: Conceptualization, Data curation, Methodology, Writing – review & editing. T.V. Phuc: Software, Writing – review & editing. A.I. Madadzada: Software, Writing – review & editing. T.Yu. Zelenyak: Software, Writing – review & editing. M. Turek: Methodology, Writing – review & editing. J. Żuk: Methodology, Writing – review & editing. C. Mita: Validation, Writing –
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The study was performed in the scope of the RO-JINR Projects no. 366 / 2021 item 81, 85; Poland-JINR Project no. 168 / 2021 item 26, JINR - Belarus Project no. 336 / 2021, item 23, JINR -Vietnam Project no. 647 item 6, Poland-JINR Project No. 120 / 2022 item 25.
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