Prof. Helge Weman

Department of Electronic Systems,

Norwegian University of Science and Technology,

NO-7491, Trondheim, Norway.

&

Founder and CSO of CrayoNano AS, NO-7037, Trondheim, Norway

 

In 2012 we outlined a generic atomic model, which describes the epitaxial growth of semiconductors on graphene that is applicable to all conventional semiconductor materials. The epitaxial model was first verified by cross-sectional transmission electron microscopy studies of self-catalyzed GaAs nanowires that grew vertically on graphene by self-assembly.1

   The epitaxial growth of semiconductors on graphene is very appealing for device applications since graphene can function not only as a replacement of the semiconductor substrate but in addition as a transparent and flexible electrode for e.g. solar cells and LEDs.2 For deep ultraviolet (UVC) AlGaN-based light emitting diodes (LEDs), in need for various disinfection and sterilization purposes, the concept offers a real advantage over present thin film-based technology. UVC LEDs are today very expensive and inefficient due to the lack of a good transparent electrode (ITO is absorbing in UVC), the high dislocation density in the active thin film layers, low light extraction efficiency, and the use of very expensive AlN substrates or AlN buffer layers on sapphire substrates.

   Motivated by this potential we are at present focused on investigating the growth of self-assembled GaN nanowires on graphene using both MOVPE and MBE.3,4 A very high nucleation yield has been achieved on untreated CVD graphene using nanometer-sized AlGaN nucleation islands. As an attempt to achieve higher uniformity and position control we have also reported on selective area MOVPE growth of AlGaN nanopyramids on graphene using a SiO2 hole-mask.5 A first proof-of-principle flip-chip UV LED was recently demonstrated using double-layer graphene, where GaN/AlGaN nanowires were grown as the light-emitting structure using plasma-assisted MBE.6 The GaN/AlGaN nanowires are found to exhibit a high crystal quality with no observable defects or stacking faults.7 Room-temperature electroluminescence measurements show a GaN related near bandgap emission peak at 365 nm with no defect-related yellow emission. 

     Our spin-off company CrayoNano are now developing UVC LEDs emitting at 275 nm based on this technology as will be further discussed in my talk.

 

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1 A.M. Munshi et al., Nano Lett. 12, 4570 (2012).

2 A.M. Munshi and H. Weman, Phys. Status Solidi RRL 7, 713 (2013).

3 M. Heilmann et al., Nano Lett., 16, 3524 (2016).

4 A. Liudi Mulyo et al., Nanotechnology, 30, 049601 (2019).

5 A.M. Munshi et al., Appl. Phys. Lett., 113, 263102 (2018)

6 I.M. Hoiaas et al., Nano Letters 19, 1649 (2019). 

7 A. Liudi Mulyo et al., Sci Rep 10, 853 (2020).