A Combination of Ion Implantation and High‐Temperature Annealing: The Origin of the 265 nm Absorption in AlN

Abstract

The commonly observed absorption around 265 nm in AlN is hampering the outcoupling efficiency of light‐emitting diodes (LEDs) emitting in the UV‐C regime. Carbon impurities in the nitrogen sublattice (CN) of AlN are believed to be the origin of this absorption. A specially tailored experiment using a combination of ion implantation of boron, carbon, and neon with subsequent high‐temperature annealing allows to separate the influence of intrinsic point defects and carbon impurities regarding this absorption. Herein, the presented results reveal the relevance of the intrinsic nitrogen‐vacancy defect VN. This is in contradiction to the established explanation based on CN defects as the defect causing the 265 nm absorption and will be crucial for further UV‐LED improvement. Finally, in this article, a new interpretation of the 265 nm absorption is introduced, which is corroborated by density functional theory (DFT) results from the past decade, which are reviewed and discussed based on the new findings.

A Combination of Ion Implantation and High‐Temperature Annealing: Donor–Acceptor Pairs in Carbon‐Implanted AlN

“…[ 7,8,13 ] In the case of neon and boron implantation, HTA leads to recovery of the crystal without measurable energetic states inside the bandgap. [ 19 ] Thus, only the oxygen‐complex‐related (and therefore HTA‐related) B/UVA band is measurable in the case of boron and neon implantation, but no further luminescence signal. Additionally, no decrease of CL intensity of the B/UVA band was measured compared to nonimplanted HTA AlN references, underlining the assumption that neon tends to diffuse out of the lattice during HTA and boron is incorporated into the Al‐sublattice without introducing energetic states within the bandgap.…”

“…Additionally, no decrease of CL intensity of the B/UVA band was measured compared to nonimplanted HTA AlN references, underlining the assumption that neon tends to diffuse out of the lattice during HTA and boron is incorporated into the Al‐sublattice without introducing energetic states within the bandgap. [ 19 ]…”

“…More details about the experimental design and parameters are published in our previous work. [ 19 ]…”

“…[ 18 ] Like shown recently, HTA is also a suited technique to anneal intrinsic point defects in AlN introduced via ion implantation, like Frenkel pairs or, in general, vacancies and interstitials. [ 19 ]…”

“…[18] Like shown recently, HTA is also a suited technique to anneal intrinsic point defects in AlN introduced via ion implantation, like Frenkel pairs or, in general, vacancies and interstitials. [19] UV-C LEDs for disinfection/sterilization purposes exhibit the largest germicidal efficacy around an emission wavelength of 265 nm. [1] Coincidentally, AlN possesses a prominent absorption line at a photon wavelength of 265 nm (corresponding to %4.7 eV photon energy), which is hampering the efficiency of these UV-C LEDs.…”