Combined study of the effect of deposition temperature and post deposition annealing on the photoluminescence of silicon quantum dots embedded in chlorinated silicon nitride thin films
Chlorinated silicon nitride (SiNx:Cl) thin films with embedded silicon quantum dots (Si QDs) were grown by remote plasma enhanced chemical vapor deposition using SiH2Cl2, H2, NH3 and Ar at different deposition temperatures (DT) in the range of 50 to 350 degC and using steps of 50 degC. After that, each sample was subjected to annealing treatments at temperatures (AT) of 400, 700 and 1000 degC. The evolution of the optical properties, composition and structure as a function of DT and AT were investigated by Null Ellipsometry, photoluminescence (PL) measurements, UV Vis spectroscopy, X ray Photoelectron Spectroscopy (XPS) Fourier Transform Infrared Spectroscopy (FTIR) scanning electron microscopy with energy dispersive X ray spectroscopy (SEM) with (EDS) and High Resolution Transmission Electron Microscopy (HRTEM) A red shift in the PL peak and an increment in the PL integrated intensity of the films was found on increasing DT from 150 to 350 degC; such changes can be explained by modifications of the matrix chemical composition and by the quantum confinement effect due to an increase in the size and density of Si QDs respectively. A chemical analysis revealed that films deposited below 150 degC suffer a post deposition oxidation process leading to the formation of silicon oxide; this process is accelerated by the temperature of the annealing treatment. Meanwhile films deposited between 150 and 350 degC are mainly composed of silicon nitride that diminishes the mentioned oxidation due to the thermal treatments and promotes the splitting of Si QDs into two populations with different average diameter. The annealed films deposited below 150 degC show a clearly decrement in the PL intensity, meanwhile the maximum emission PL peak from annealed films grown from 150 to 350 degC shifts to high emission energies. This post thermal annealing blue shift can be mainly related to the nucleation of new small Si QDs. We concluded that temperature is one of the most important mainstays to achieve good luminescence from Si QDs.