Effect of the Graded Silicon Content in SRN/SRO Multilayer Structures on the Si Nanocrystals and Si Nanopyramids Formation and Their Photoluminescence Response.

José Juan Avilés Bravo,Karla Esther González Flores,Santiago Antonio Cabañas Tay,Alfredo Morales Sánchez,Liliana Palacios Huerta,Mario Moreno Moreno,Javier Flores Méndez

doi:10.3390/ma14216582

Abstract

Two multilayer (ML) structures, composed of five layers of silicon-rich oxide (SRO) with different Si contents and a sixth layer of silicon-rich nitride (SRN), were deposited by low pressure chemical vapor deposition. These SRN/SRO MLs were thermally annealed at 1100 °C for 180 min in ambient N2 to induce the formation of Si nanostructures. For the first ML structure (MLA), the excess Si in each SRO layer was about 10.7 ± 0.6, 9.1 ± 0.4, 8.0 ± 0.2, 9.1 ± 0.3 and 9.7 ± 0.4 at.%, respectively. For the second ML structure (MLB), the excess Si was about 8.3 ± 0.2, 10.8 ± 0.4, 13.6 ± 1.2, 9.8 ± 0.4 and 8.7 ± 0.1 at.%, respectively. Si nanopyramids (Si-NPs) were formed in the SRO/Si substrate interface when the SRO layer with the highest excess silicon (10.7 at.%) was deposited next to the MLA substrate. The height, base and density of the Si-NPs was about 2–8 nm, 8–26 nm and ~6 × 1011 cm−2, respectively. In addition, Si nanocrystals (Si-ncs) with a mean size of between 3.95 ± 0.20 nm and 2.86 ± 0.81 nm were observed for the subsequent SRO layers. Meanwhile, Si-NPs were not observed when the excess Si in the SRO film next to the Si-substrate decreased to 8.3 ± 0.2 at.% (MLB), indicating that there existed a specific amount of excess Si for their formation. Si-ncs with mean size of 2.87 ± 0.73 nm and 3.72 ± 1.03 nm were observed for MLB, depending on the amount of excess Si in the SRO film. An enhanced photoluminescence (PL) emission (eight-fold more) was observed in MLA as compared to MLB due to the presence of the Si-NPs. Therefore, the influence of graded silicon content in SRN/SRO multilayer structures on the formation of Si-NPs and Si-ncs, and their relation to the PL emission, was analyzed.

Highlights

Introduction iationsOver the last several decades, silicon nanocrystals (Si-ncs) have been the subject of intensive study due to their potential applications as a strong light source [1,2,3,4]
The Si2p, O1s and N1s signals were obtained in X-ray photoelectron spectroscopy studies (XPS) depth profiles by gradually etching the silicon-rich nitride (SRN)/silicon-rich oxide (SRO) ML structure to record the corresponding signals at different depths until the
This effect has previously been related to the high temperature of annealing (1100 ◦ C), which promotes the diffusion of the Si and O atoms from the SRO layers with higher atomic percentage towards the SRO layers with lower percentages, generating the gradual interfaces

Summary

Introduction

Introduction iationsOver the last several decades, silicon nanocrystals (Si-ncs) have been the subject of intensive study due to their potential applications as a strong light source [1,2,3,4]. Si-ncs are mostly obtained in single layers of Si-rich dielectric materials [7,8]. A broad Si-nc size distribution was obtained in these single layers. It is possible to control the size and density of Si-nc by employing a technique that allows the deposition of multilayer (ML) structures of Si-rich dielectric materials [9,10]. This ML approach makes it possible to engineer the bandgap energy of Si-ncs by optimizing the layer thickness and the composition (x, y or z < 2) of the SiOx /SiOy /SiOz layers that form the ML structure.

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