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Posted: Jun 25, 2013

A breakthrough in nanowire growth: Quantitative in-situ monitoring for process optimization

(Nanowerk News) Nanowires (sometimes also called nanorods) are becoming more and more attractive for next generation LED and solar cell applications. One of the reasons is the fact that epitaxial III-V nanowire arrays combine 1-dimensional electronic states with additional degrees of freedom for strain relaxation and resonant electromagnetic interaction. The most critical parameters for nanowires’ optical response are their length and diameter.
Usually, time consuming and destructive ex-situ methods like scanning electron microscopy (SEM) are used for characterization before further processing. But now, LayTec and the Nanometer Structure Consortium at Lund University (nmC@LU) in Sweden have jointly developed a solution for real-time quantitative monitoring of III-V nanowire growth.
The first results were presented by Martin Magnusson of Lund University at LayTec‘s in-situ seminar on June 3. The team of Prof. Lars Samuelson used LayTec’s spectroscopic in-situ reflectometer EpiR to monitor the nanowire epitaxial process in an AIXTRON 200/4 reactor. Fig. 1 shows an MOVPE run sequence where InP shells were grown on InP core nanowires.
software display after a complete nanowire growth run
Fig. 1: LayTec software display after a complete nanowire growth run. In the color plot (left), the reflectance is given by the color.
The data of previous ex-situ analysis by SEM (see Fig. 2) and spectroscopic reflectance 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 ("Optical Far-Field Method with Subwavelength Accuracy for the Determination of Nanostructure Dimensions in Large-Area Samples").
SEM image of InP nanowires
structured with gold particles by nanoimprint lithography
Fig. 2: SEM image of InP nanowires structured with gold particles by nanoimprint lithography.
Together with these algorithms, the in-situ spectroscopic measurements by EpiR provide information on the evolution of nanowire length and diameter already during growth. According to Nicklas Anttu of Lund University, “The first results are very impressive. EpiR enables effective process optimization, speeds up development and paves the way to future process transfer for industrial nanowire growth. We are confident that in-situ metrology will be a must in nanowire applications in the near future.“
Source: LayTec
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