LayTec AG of Berlin, Germany, which makes in-situ metrology systems for thin-film processes, focusing on compound semiconductor and photovoltaic applications, and Sweden's Nanometer Structure Consortium at Lund University have jointly developed a solution for real-time quantitative monitoring of III-V nanowire growth.
First results were presented by Martin Magnusson of Lund University at LayTec's in-situ seminar on 3 June. Professor Lars Samuelson and his team used LayTec's spectroscopic in-situ reflectometer EpiR to monitor the nanowire epitaxial process in an Aixtron 200/4 reactor. Figure 1 shows a metal-organic vapour-phase epitaxy (MOVPE) run sequence where InP shells were grown on InP core nanowires.
Video: In-situ monitoring of nanowire growth run, courtesy of LayTec and YouTube.
The data of previous ex-situ analysis by SEM (see Figure 2) and spectroscopic reflectance [1] were used by Nicklas Anttu of Lund University to develop numerical algorithms for deduction of the average length and diameters of the growing nanowire ensemble (N. Anttu et.al, 'Optical Far-Field Method with Subwavelength Accuracy for the Determination of Nanostructure Dimensions in Large-Area Samples', Nano Lett., 2013, 13 (6), p2662).
Together with these algorithms, the in-situ spectroscopic measurements by EpiR provide information on the evolution of nanowire length and diameter already during growth.
"The first results are very impressive," says Nicklas Anttu of Lund University. "EpiR enables effective process optimization, speeds up development and paves the way to future process transfer for industrial nanowire growth," he adds. "We are confident that in-situ metrology will be a must in nanowire applications in the near future."
Nanowires (or nanorods) are becoming increasingly attractive for next-generation LED and solar cell applications, says LayTec. One of the reasons is that epitaxial III-V nanowire arrays combine one-dimensional electronic states with additional degrees of freedom for strain relaxation and resonant electromagnetic interaction.
