Exploring swift-heavy ion irradiation of InGaN/GaN multiple quantum wells for green-emitters: the use of Raman and photoluminescence to assess the irradiation effects on the optical and structural properties

Abstract

The effects of ¹²⁹Xe swift-heavy ion (SHI) irradiation on the optical and structural properties of InGaN/GaN multiple quantum wells (MQWs) are studied using non-destructive optical spectroscopy techniques. Through excitation wavelength-dependent μ-Raman spectroscopy, it is possible to identify the damage profile and to notice the surface region (around the first 40 nm) as the most affected one. Independent Rutherford backscattering spectrometry in channelling mode experiments corroborate this. By using resonant excitation with InGaN electronic states, it is possible to observe an increase of the A₁(LO)_InGaN phonon intensity for higher SHI energies. This is attributed to intermixing at the MQWs’ interfaces for electronic energy losses above 20 keV nm⁻¹. Photoluminescence studies reveal an intense yellow emission band (YB) with two distinct contributions: excitonic (InGaN) and deep-level defects (GaN). After irradiation, strong luminescence intensity quenching and a change in its excitation mechanisms occur. The YB is no longer excited with energy above the GaN bandgap, but instead through an excitation band (at about 2.75 eV) attributed to gallium vacancies introduced in the GaN barriers. The strong quenching of the luminescence reveals that SHI irradiation introduces detrimental defects in the structure, which may compromise its use (without additional post-implantation treatments) for obtaining more efficient green light emitters based on InGaN/GaN MQWs.