Etching of the SiGa_xN_y Passivation Layer for Full Emissive Lateral Facet Coverage in InGaN/GaN Core–Shell Nanowires by MOVPE

Abstract

To strongly enhance the vertical growth rate in MOVPE-grown GaN core−shell wires, large quantities of silane (SiH 4 ) need to be introduced for the growth of the wire core. This results in the formation of a SiGa x N y layer that acts effectively as a dielectric mask on the sidewalls of the GaN core, thereby promoting vertical growth. While its presence is useful during core growth, it precludes the formation of homogeneous core−shell heterostructures, whose coverage and optical quality tend to be maximized at the top of the wires. In this paper, we propose three different strategies to remove this passivating layer once its initial role is accomplished. They are based on chemical, physical, or thermal etching. Their effects on the optical quality of subsequent core−shell InGaN/GaN heterostructures, including single and multiple-quantum-well heterostructures, have been analyzed. Overall, an ex situ chemical etching of SiGa x N y by H 3 PO 4 results in an enhanced emissive coverage and a stronger overall luminescence intensity from the active regions, while simultaneously removing deep-defect emissions arising from the high growth temperature of the core.

Complications in silane-assisted GaN nanowire growth

“…20 Although this Si-rich layer deteriorates the quality of the InGaN shell layers grown outside of it, 21–23 its impact can be reduced and high quality core–shell structures can be achieved by optimising the structures 21,22 or removing the Si-rich layer prior to the growth of InGaN shell layers. 23…”

“…16,18,19 Second, GaN nanowires grown by this method oen exhibit a simultaneously formed Si-rich layer on the sidewall facets 15,[20][21][22] This Si-rich layer was reported to be responsible for the growth rate enhancement by preventing further deposition of GaN on the sidewall facets. 20 Although this Si-rich layer deteriorates the quality of the InGaN shell layers grown outside of it, [21][22][23] its impact can be reduced and high quality core-shell structures can be achieved by optimising the structures 21,22 or removing the Si-rich layer prior to the growth of InGaN shell layers. 23 Despite the wide adoption of this method, questions remain about the growth mechanism.…”

“…20 Although this Si-rich layer deteriorates the quality of the InGaN shell layers grown outside of it, [21][22][23] its impact can be reduced and high quality core-shell structures can be achieved by optimising the structures 21,22 or removing the Si-rich layer prior to the growth of InGaN shell layers. 23 Despite the wide adoption of this method, questions remain about the growth mechanism. Tessarek et al, attributed the fast growth rate to the passivating Si-rich layers on the sidewall facets, which increases the amount of Ga adatoms arriving at the growth front at the top surface, thus enhancing the growth rate for the -c (000 1) plane.…”