Exciton states and photoluminescence of silicon and germanium nanocrystals in an Al 2 O 3 matrix
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NSIONAL SYSTEMS
Exciton States and Photoluminescence of Silicon and Germanium Nanocrystals in an Al2O3 matrix I. M. Kupchak, Yu. V. Kryuchenko, D. V. Korbutyak, A. V. Sachenko, É. B. Kaganovich^, É. G. Manoœlov, and É. V. Begun a Lashkarev
Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev, 03028 Ukraine ^e-mail: [email protected] Submitted September 11, 2007; accepted for publication October 30, 2007
Abstract—This paper deals with the theoretical and experimental study of radiative processes in zero-dimensional Si and Ge nanostructures consisting of a system of Si or Ge nanocrystals embedded in an Al2O3 matrix. The Al2O3 films containing Si or Ge quantum dots were produced by pulsed laser-assisted deposition. The timeresolved photoluminescence spectra of the films were recorded in the energy range from 1.4 to 3.2 eV in the range of photoluminescence relaxation times between 50 ns and 20 µs. The exciton binding energy and the energy of radiative excitonic transitions are calculated, taking into account the finite barrier height and the polarization of heterointerfaces. In addition, the excitonic photoluminescence spectra are calculated, taking into account the effect of quantum mesoscopic fluctuations and the possible nonmonotonically varying dependence of the radiative zero-phonon lifetime of excitons on the dimensions of the quantum dots. The observed agreement between the calculated and recorded photoluminescence spectra confirms the excitonic nature of photoluminescence and provides a means for the determination of the model parameters of photoluminescence in the nanostructures. PACS numbers: 78.55.Hx, 78.67.Bf, 81.07.Ta, 81.15.Fg, 81.16.Mk, 81.40.Tv DOI: 10.1134/S1063782608100096
1. INTRODUCTION One of the most extensively studied objects of nanophysics is films that contain quantum dots (QDs) formed by indirect-gap semiconductor nanocrystals (NCs), Ge or Si NCs. Such films exhibit photoluminescence (PL) in the visible spectral region at room temperature. It has been established that, in nature, the visible PL is associated with the quantum-confinement effect in Si and Ge NCs embedded in Si or Ge oxide matrices. Most studies have dealt with Si oxide films containing Si NCs. At the same time, a search is being conducted for alternative matrices, in which the band gap is sufficiently large to form a potential barrier at the interface between the Si or Ge NCs and the matrix and in which, at the same time, the permittivity is such that provides the dielectric amplification effect and, in addition, a high density of the NCs. The requirements additionally imposed upon the barrier layer of the QDs are thermodynamic stability, lack of interaction with the NC material, etc. There are a few publications [1] that report the observation of visible PL at room temperature in films containing Si nanoparticles in the Al2O3 matrix. The choice of the Al2O3 barrier layer for Si QDs is governed by the fact that the permittivity of Al2O3 (ε = 9) is larger than that of SiO2. This allows one to obta
