Optik 123 (2012) 887–891 Contents lists available at ScienceDirect Optik jou rnal homepage: www.elsevier.de/ijleo Phase mixture and anti-reflection window in visible of annealed beryllium-nitride thin films on silicon crystal Conett Huerta Escamilla a , Fabio Chale Lara a,b,c , Mario H. Farías a , Mufei Xiao a,∗ a Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Apartado Postal 365, Ensenada, Baja California CP 22800, Mexico b Centro de Investigación Científica y de Educación Superior de Ensenada, Apartado Postal 2681, Ensenada, Baja California CP 22800, Mexico c CICATA-IPN Unidad Altamira, Km. 14.5 Carretera, Tampico-Puerto Industrial, Altamira, Tamps CP 89600, Mexico a r t i c l e i n f o Article history: Received 16 January 2011 Accepted 20 June 2011 Keywords: Be3N2 thin films Pulsed laser sputtering Optical reflection spectroscopy a b s t r a c t Beryllium-nitride (Be 3 N 2 ) thin films were grown on silicon Si(1 1 1) substrates by pulsed laser deposition in a RIBER LDM-32 system, and characterized with in/ex situ XPS and SIMS. The structure of the films was analyzed with XRD. The films were further analyzed for surface topographic information with SEM and profilometry, and for optical properties with optical spectroscopy. It was observed that the material, prepared at room temperature and annealed at 700 ◦ C for 2 h, had undergone a partial phase transition to a mixture of amorphous and crystalline phases, and the thin films showed a large anti-reflection window in the visible. Therefore, the annealed Be 3 N 2 thin films would be potentially useful for stable electronic packaging with desired photonic features. © 2011 Elsevier GmbH. All rights reserved. 1. Introduction Beryllium nitride (Be 3 N 2 ) in thin film format has rarely been studied for its optical properties or considered for applications in optoelectronics [1], in part due to the toxic nature of beryllium. In recent times, nitride based materials were however widely adapted for short wavelength light emissions [2–4], thanks to the large energy gap between the valence and conduction bands. For group III–V nitrides, the channel for the inter-band transit is usually direct and the light emission caused by the transit can reach up to the ultraviolet [5,6]. On the other hand, beryllium is a light and elastic metal of very high melting point, and its alloys are widely used for coating and packaging in hazardous environments. In addition, beryllium nitrides as well as other nitride materials are good thermal insula- tors with high temperature stability and chemical resistance [7–9]. However, unlike AlN thin films that bear rich phase and photonic features [10–12], Be 3 N 2 thin films are usually less optically active in the visible and may cause significant absorption and reflection [1,7]. Otherwise, the composite can be a good candidate as coat- ing or packaging material for silicon based optoelectronic devices. It is usually desirable that the coating has tunable transparency or anti-reflection capabilities in certain optical frequency ranges. Two concerns may arise in considering coating Be 3 N 2 on sili- con based devices. Firstly, one has to choose a suitable deposition ∗ Corresponding author. E-mail address: mufei@cnyn.unam.mx (M. Xiao). method that is able to deposit highly controllable thin films on sili- con substrate. Secondly one wants to engineer the thin film so that it allows light in a given optical frequency range to be coupled into thin film modes and no light is reflected back. The anti-reflection coat is especially useful for highly efficient solar absorption with silicon. In the present work, we have found satisfactory solutions to the two concerns. We have developed a stable deposition process based on pulsed laser sputtering so that uniform Be 3 N 2 thin films can be grown on silicon crystal Si(1 1 1) surface and the thickness of the thin films is controllable within a few nanometers. However, a drawback of the process was found that the formed thin films were mostly in amorphous state without crystalline features, which is consistent with previous findings [1]. For this reason, the films remained largely in metallic phase and significant optical absorp- tion and reflection were observed in the visible. In order to increase the portion of crystalline structures in the thin films, we increased the deposition temperature up to 700 ◦ C, and the resulting films were found to contain significant crystalline components but the optical reflection spectrum remains of a simple increasing func- tion. Eventually, we have found the solution for at least a partial phase transit. We first deposited the film at room temperature. After the deposition, the film was annealed at 700 ◦ C for 2 h. In this case, the reflection spectrum contains apparent interference patterns, indicative of a dielectric phase. In other words, the films were found in a mixture of amorphous and crystalline structures. It is interesting to note that the annealed thin film opens a large anti-reflecting window in-between two broadened reflecting and absorbing peaks, which is due to the fact that the thin film becomes 0030-4026/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijleo.2011.06.058