Visible photoluminescence from Ge nanoclusters implanted in nanoporous aluminum oxide films

Abstract Nanoporous aluminum oxide (Al 2 O 3 ) films with uniform porous size of 45 nm prepared by the electrochemical process in inorganic acid medium were implanted at room temperature (RT) with 120 keV Ge + ions with a fluence of 1.2×10 16  cm −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 5456 A consistent with emission band characteristics of nanocluster of Ge with diameter in the range of 4–8 nm, 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 172 A and the emission intensity decreases significantly, strongly suggesting that nanocrystalline Ge having a character of direct optical transitions exhibits the visible photoluminescence.