Sag nanowire growth with a planarization process

A method for manufacturing a nanowire structure comprising:

• providing a substrate;
• forming a buffer region over the substrate;
• eliminating a sacrificial top portion of the buffer region to provide a buffer layer with a planarized top surface, wherein:
• the planarized top surface has a surface roughness below 10 Å;
• and
• the buffer layer comprises a plurality of discrete layers;
• forming a patterned mask over the planarized top surface of the buffer layer, wherein the patterned mask comprises an opening through which a portion of the planarized top surface of the buffer layer is exposed;
• and
• forming a nanowire after the patterned mask is formed, wherein the nanowire is formed over the exposed portion of the planarized top surface of the buffer layer through the opening of the patterned mask, and the nanowire protrudes vertically beyond a top surface of the patterned mask, wherein:
• the substrate comprises gallium antimonide (GaSb);
• within the buffer layer, at least one of the plurality of discrete layers comprises aluminum gallium arsenide antimonide (AlGaAsSb);
• and
• the nanowire is formed of indium arsenide (InAs), wherein the buffer layer is configured to provide electrical confinement and isolation between the substrate and the nanowire.