Bandgap engineering across telecom wavelengths of InN nanowires by post-growth hydrogen irradiation

III-V semiconductor nanowires (NWs) provide significant versatility in the manipulation of their optical and electronic characteristics and, crucially, may accommodate quantum-confined structures such as quantum dots (QDs), which serve as foundational elements for photonic and optoelectronic devices. Quantum structures are often created in NWs throughout the growth process by alternating sections with differing bandgaps or different crystal phases. However, this conventional approach can result in a limited capability in controlling the dots’ size and emission energy. Therefore, we are working on a new, post-growth approach for forming QDs whose size and energy can be finely controlled. Our approach focuses on InN NWs monolithically grown by MBE on Si substrates through autocatalysis thanks to the use of an In seeding layer [1]. In bulk InN, post-growth hydrogen irradiation was shown to increase the bandgap energy due to the formation of a 4-H complex between In, N and H [2]. If this incorporation is carefully controlled at the nanoscale within a NW, it could potentially enable bandgap modulation along the same NW, leading to the formation of QDs. To achieve this goal, we have optimized low-energy hydrogen irradiation of InN NWs that leads to on demand post-growth bandgap engineering. By µ-PL spectroscopy on single NWs we demonstrated a giant bandgap tuning of the NWs, with a blueshift of almost 0.5 eV with respect to the pristine NW (emitting at ~1900 nm) and passing through the range 1100 nm - 1500 nm thus including telecom wavelengths. We also investigated possible strain effects and defects-induced effects on hydrogenated InN NWs by spatially resolved µ-Raman spectroscopy. Hydrogen incorporated in the NWs can be partially or fully removed through thermal annealing so we used this technique to further fine-tune the bandgap of hydrogenated InN NWs and to reverse the emission energy of hydrogenated to pristine NWs. We have also investigated the possibility of achieving a localized annealing through spatially-resolved laser annealing [3]. We are actively working on developing new methods to advance H-based bandgap engineering control down to the nanoscale, with the goal of creating QDs. Besides for the quantum optics applications based on QDs, the giant bandgap tunability of InN NWs across the solar spectrum is ideal for optoelectronics and photo-voltaic applications.