Effect of Be‐doping on InGaN/GaN nanocolumn light‐emitting diode structures by rf‐plasma‐assisted molecular‐beam epitaxy

Abstract

GaN nanocolumns are one‐dimensional high‐quality dislocation‐free nano‐crystals. The effect of Be‐doping on GaN nanocolumns was investigated using InGaN/GaN nanocolumn LED structure grown by RF‐plasma‐assisted molecular‐beam epitaxy. Be was doped into the upper cladding region of the nanocolumn light‐emitting diodes (LEDs). Be is expected to be a p‐type dopant of GaN with a shallow accepter level, but p‐type conductivity was not obtained in these experiments. However, we observed a remarkable enhancement of the lateral growth of the GaN nanocolumn by Be doping; that is, the surface of the Be‐doped region became smooth and continuous with increasing Be doping concentration. The root mean square (RMS) surface roughness was reduced from 35 to 10 nm with increasing Be cell temperature from 710 to 975 °C. Cross‐sectional TEM observation revealed that no threading dislocations were generated in the observed area at the conjunction boundary between neighboring nanocolumns during lateral growth. This suggests that a high‐quality overgrowth layer with a low threading dislocation density can be realized on Be‐doped GaN nanocolumns. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Properties of GaN-based nanopillar-shaped crystals grown on a multicrystalline Si substrate

“…It has been also said that the variation originates in increases of lateral growth rates in heavily doped nanostructure crystals which are grown on single crystalline substrates. 23,26 Similar effects might occur in the films reported here though the mechanism for the enhancement of the lateral growth rate in this case is still not clear.…”

Overgrowth of GaN on Be-doped coalesced GaN nanocolumn layer by rf-plasma-assisted molecular-beam epitaxy—Formation of high-quality GaN microcolumns

“…As reported in Ref. [9], Be doping into the GaN nanocolumns enhanced the lateral growth of nanocolumns to produce a smooth and continuous film on the top surface; the root-mean-square (RMS) surface roughness obtained by atomic force microscope (AFM) observation was markedly reduced from 35 to 10 nm over an area of 20 mm  20 mm upon increasing the Be cell temperature (T Be ) from 710 to 975 1C. From cross-sectional and plan-view transmission electron microscope (TEM) observations of the Be-doped nanocolumn grown at T Be =920 1C, it was observed that the nanocolumn size increased in the Bedoped region due to lateral growth, but the coalescence between nanocolumns was insufficient.…”

“…However, the presence of the 5-nm-thick InGaN layer and the short growth time of the GaN nanocolumns do not change the surface morphology. The RMS surface roughnesses with the nanocolumn platforms of T Be =920 and 975 1C were 22.5 and 10.4 nm, respectively [9].…”

“…We reported the epitaxial overgrowth of a continuous GaN film on GaN nanocolumns in 2002 [7], and then the enhancement effect of Mg doping on coalesced GaN nanocolumns was utilized for the fabrication of InGaN/GaN nanocolumn LEDs [8]. Very recently, we have reported that Be doping had a superior enhancement effect on the lateral growth of GaN nanocolumns [9]. GaN overgrowth on GaN nanocolumns can provide a new fabrication technique for GaN substrates because of the easy removal of the substrates.…”

Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

“…Kishino's group first reported the coalescence of top GaN NWs on a silicon substrate. 91,92 They found that Be-or Mg-doping of GaN can remarkably enhance the lateral growth and eventually obtain a smooth and continuous layer with increasing Mg doping concentration. A similar approach was also applied to AlGaN-based UV-A NWs-LED in which the coalesced p-GaN contact layer was successfully demonstrated with the advantage of eliminating the polymer-filling planarization step, thus simplifying fabrication.…”