= Solution
Across a radial section, the narrow-gap <indium gallium nitride> layer lies between wider-gap n-GaN and p-GaN. A suitable <type-I band alignment> has a downward conduction-band offset and upward valence-band offset in the <indium gallium nitride>, confining <electrons> and holes to the active layer. The original band sketch isolates those offsets; the complete junction also has doping-induced <band bending>.
At <thermal equilibrium> the <Fermi level> is common throughout. Forward bias separates the <electron> and hole <quasi-Fermi levels>, injects carriers from the n- and p-regions and permits <electron-hole recombination> in the thin active layer. A full radial line through the wire crosses two copies of the shell well; a core-to-exterior radial coordinate crosses one.
\b[The 5 nm <indium gallium nitride> shell is the <quantum well> active region, not a metallic contact.] Finite band offsets, confinement and polarization fields affect its transition <energy>; the bulk gap alone is insufficient.
A plausible role for the SiN mask is selective-area growth: restrict nucleation to exposed windows and suppress parasitic deposition between wires. Retained insulating material can also help prevent unwanted electrical paths during later processing. Which role dominates depends on the actual fabrication sequence. The cited source concerns core-shell single-wire LEDs and contact engineering, so a qualitative band sketch does not reproduce its complete device model.<InGaN GaN Core-Shell Single Nanowire Light Emitting Diodes with Graphene-Based P-Contact by Maria Tchernycheva and others>[2014, pp.2456–2465, device/material system and contact architecture]{ref}
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