Visible photoluminescence from Ge nanoclusters implanted in nanoporous aluminum oxide films

Abstract

Nanoporous aluminum oxide (Al2O3) films with uniform porous size of 45nm prepared by the electrochemical process in inorganic acid medium were implanted at room temperature (RT) with 120keV Ge+ ions with a fluence of 1.2×1016cm−2. The nucleation and growths of Ge nanoparticles, were obtained by thermal annealing of the implanted samples at the temperature range of 200–600°C. The size and distribution of the nanoparticles were characterized by photoluminescence (PL) measurements. The photoluminescence measurements as a function of the annealing temperature shows that at low annealing temperature (200°C), the sample presents a low intensity and broad emission band centered at 5456Å consistent with emission band characteristics of nanocluster of Ge with diameter in the range of 4–8nm, as the annealing temperature increases to 400°C the PL intensity increases by a factor of almost 20 and the emission band suffers a small red shift. The intensity increases can be related to the increase of the number of Ge nanocluster. At the annealing temperature of 600°C, the emission band is considerably red shifted by almost 172Å and the emission intensity decreases significantly, strongly suggesting that nanocrystalline Ge having a character of direct optical transitions exhibits the visible photoluminescence.