III-nitride nano-crystals, such as nanocolumns [1] are attractive candidate for opto-electronic devices, for the sake of their dislocation free-nature, strain-relaxation effect and high light extraction efficiency. For the application of nano-crystals, suitable device structure and accurate shape and position control are required.

Recently we have fabricated InGaN/GaN nanocolumn LEDs on flexible metal sheet. After the growth of n-GaN nanocolumn and InGaN/GaN quantum disks on (111) Si substrate by rf-plasma assisted molecular beam epitaxy, the lateral growth of p-GaN was enhanced to make continuous film at the top surface [2]. Pt/Au (50mm) electrode was formed on the p-side surface and then Si was selectively removed. After filling the interstice of n-GaN nanocolumns with spin on glass, tips of the nanocolumns were exposed in circular (f=400mm) then ITO transparent electrodes were deposited. The nanocolumn LED showed red (663nm) emission under 10mA DC drive.

The size and position fluctuation of self-assembled InGaN/GaN nanocolumns cause broadening of emission spectra. Selective area growth (SAG) of GaN nano-crystals is a key technology to overcome this problem. For the SAG of nano-crystals, (0001) GaN templates coated with nano-patterned Ti (~5nm) were used as substrate. Holes or stripe windows with diameter or width of around 100~400nm were open to appear the GaN surface. When the growth temperature was above 900^oC, GaN nano-crystals were grown only on the window area with side facets normal to the substrate surface. Well aligned nanocolumns [3] and plate-like thin nano-crystals (nanowalls) [4] were grown.
This study was partly supported by a Grant-in-Aid for Scientific Research on Priority Areas #18069010 and (B) #21310087 from MEXT.

[1] M. Yoshizawa et al, Jpn. J. Appl. Phys. 36 (1997) L459. [2] A. Kikuchi et al, Jpn. J. Appl. Phys. 43 (2004) L1524. [3] H. Sekiguchi et al, Appl. Phys. Express 1, (2008) 124002. [4] A. Kikuchi et al, MRS Fall Meeting, Q4.6, USA (2007).

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1. Room temperature stimulated emission from self-organized GaN nano-columns grown on (111) Si substrate