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esearch Letter

Emitting modification in Si-rich-SiNx films versus silicon nitride compositions T. Torchynska, Instituto Politécnico Nacional, ESFM, México DF, 07738, México G. Polupan, Instituto Politécnico Nacional, ESIME, México DF, 07320, México L. Khomenkova, V. Lashkaryov Institute of Semiconductor Physics at NASU, Kyiv, 03028, Ukraine A. Slaoui, ICube, 23 rue du Loess, BP 20 CR, 67037 Strasbourg Cedex 2, France Address all correspondence T. Torchynska, L. Khomenkova at [email protected]; [email protected] (Received 27 April 2017; accepted 31 May 2017)

Abstract SiNx films were grown by plasma-enhanced chemical vapor deposition on Si substrates with the composition controlled by the flow ratio R: ammonia to silane in the range R = 0.45–1.0. Then SiNx films were annealed at 1100 °C for 30 min to form Si-quantum dots (QDs). Fourier transform infrared spectroscopy study permits estimating SiNx compositions. Photoluminescence (PL) spectra of SiNx films included bands peaked at: 2.87–2.99, 2.42–2.54, 2.10–2.25, and 1.47–1.90 eV. Former three PL bands are attributed to emission via defects in SiNx films. Fourth PL band is assigned to exciton emission in Si QDs, detected by transmission electron microscopy study in films grown at R ≤ 0.67. The nature of non-radiative defects in SiNx films is discussed as well.

Introduction Silicon nitride (Si3N4)-based materials have been extensively investigated in the last decades owing to their interesting chemical, mechanical, and optical properties.[1] The creation of Si-quantum dots (QDs) in a SiNx host offers the several key advantages over Si oxide.[2] Silicon nitride is a more promising matrix for Si-QDs due to its structural stability at electronic technology processing. Better electrical properties owing to the lower tunneling barrier allow the transport of electrons and holes into Si-QDs embedded in SiNx.[3] Additionally, the Si-QDs coordinated with oxygen atoms are subject to charge trapping at the interface states, which limit the energy of emission quantas from Si-QDs to 0.8, almost all excess Si atoms have been coagulated into Si-QDs. But the SiNx films fabricated with lower R still demonstrate the presence of excess Si [Fig. 1(c)]. Room-temperature PL spectra of annealed samples demonstrate the variation of their shape versus film compositions (Fig. 2). With R decreasing the PL spectra demonstrate the appearance of asymmetry in the low-energy side (Fig. 2). The total PL peak position has shifted toward the lower energies, but it does not demonstrate a systematic shift with R (Fig. 2). The analysis of PL spectra has revealed that all PL spectra can be decomposed (Fig. 3) on four PL bands with the maxima at: 2.87–2.99 eV (A), 2.42–2.54 eV (B), 2.10–2.25 eV (C), and 1.47–1.90 eV (D) in different samples. It is clear that PL peaks

A, B, and C dominate in PL spectra of films grown at R = 0.71– 1.0 (Fig. 2). The PL peaks A, B, and C shift at nearly 120 meV: from 2.99, 2.54, 2.25 eV down to 2.87, 2.42, 2.13 eV, respectively, with R decreasing (Fig. 2). In SiNx films grown at R = 0.59–0.6