Analysis and control of emission properties of InGaN-on-GaN nanocolumns grown by molecular-beam epitaxy on Si(111) substrates.
Résumé
Self-assembled InxGa1-xN nanocolumns (NCs) were fabricated by plasma-assisted MBE on Si(111) substrates. The samples were analyzed by continuous-wave and time-resolved photoluminescence (PL) in order to gain control about the emission characteristics by changing the growth parameters. NCs were grown on Si (111) in a two-step procedure: (i) growth of GaN NCs at 800 ºC and (ii) growth of InGaN NCs on top of the GaN NCs at different sample temperatures (from 650 ºC to 750ºC) with the same nominal flux of In and Ga. This growth approach was chosen due to a drastic suppression of non-radiative recombination centers inside the NCs, a significant enhancement of the internal quantum efficiency and a superior light extraction efficiency. Within the growth temperature range of 650 to 750 °C, an increase in In incorporation for decreasing temperature is observed. This effect allows tailoring the InGaN nanocolumns emission line shape by using temperature gradients during growth. Depending on the gradient rate, span, and sign, broad emission line shapes are obtained, covering the yellow to green range, even yielding white emission.