Photoluminescence spectroscopy and transport electrical measurements reveal the quantized features of Si nanocrystals embedded in an ultra thin SiO₂ layer

Abstract

In this paper, we have investigated the quantized charging features revealed by nanometer scale devices containing a 2D array of Si nanoparticles (nps) embedded into a SiO 2 layer. The Si nps were synthesized by ultra low energy ion implantation and annealing under slightly oxidizing ambient. The structural characteristics of the material (oxide thicknesses, nps size and density) have been studied by Transmission Electron Microscopy (TEM) and Energy Filtered TEM (EFTEM). Moreover, photoluminescence (PL) spectroscopy and electrical I(V) measurements using a MOS capacitor addressing only a few nps have been performed at room temperature. It is observed that, as the oxidizing annealing temperature increases, the nps size decreases and the oxide quality is restored. These features appear on the PL spectra as a blue shift of the PL red band linked to quantum confinement into nps and on the I(V) characteristics as an increase of the voltage peak width and a decrease of the main current background. 1 Introduction The quantized charging features like Coulomb blockade and single tunnelling effects revealed in nps must operate at room temperature (RT) to make single electron devices attractive for memory applications. In this context nps measuring less than 10 nm are candidates for single electron memory, where addition or subtraction of an electron represents a bit of data. With this aim in mind, nanocrystal memory is an alternative to conventional non volatile memory because of its high charge storage and low power consumption [1,2]. Among different techniques [3][4][5], ultra low energy ion implantation (ULE-II) allows the formation of a two dimensional (2D) array of Si nps. Using this technique, a high dose of silicon (~2x10 16 ions/cm 2 ) is implanted with an energy of 1 keV into thin oxide layers followed by thermal annealing (900 °C to 1000 °C) classically under N 2 . Varying the implantation conditions allows a fine control of the position, size and surface density of the nps [6,7]. We thus obtain a 2D array of silicon nps, with a controlled size and surface density, positioned at a tunnelling distance from the SiO 2 /Si interface. Some recent studies have shown that an improvement of the oxide quality, and in particular of the control oxide, is obtained when annealing under N 2 +1.5%O 2 instead of N 2 [7,8]. This oxide healing is possible thanks to the oxidation of the Si in excess present in the matrix after implantation [9]. However, various implantation damages (dangling bonds, excess silicon) are still present in the matrix and strongly affect the integrity of the oxide and thus the quantized effects in the nps. In this paper, we investigate this device by studying various characteristics as structural (TEM), photolumi-