Identification of point defects using high-resolution electron energy loss spectroscopy

Although there are many techniques that can detect bandgap states associated with point defects in the lattice, it is not routinely possible to determine the type of defect at submicron spatial resolution. Here we show that high-resolution electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope can locate and identify point defects with a resolution of about 10 nm in a wide-bandgap BAlN semiconductor. B interstitials, N vacancies, as well as other point defects have been experimentally detected using EELS and have been identified using density functional theory.

Figure 1

HAADF images of AlN/BAlN heterostructures, with a B/(B+Al) ratio of (a) 0.12, and (b) 0.18. The B concentrations in the numbered regions are estimated from the $Z$ contrast and are listed in Table 1.

Figure 2

(a) EELS low-loss spectra in the energy range below 1 eV of the sample with $\mathrm{B}/\left(\mathrm{B}+\mathrm{Al}\right)=0.18$. (b) HAADF image showing the positions where the spectra in (a) were acquired. The $Z$ contrast of this image is poor for BAlN/AlN interface, under this certain acquisition condition.

Figure 3

EELS low-loss spectra of a scanned region in the BAlN films with a B/(B+Al) ratio of (a) 0.18 and (b) 0.12, with background-subtracted spectra shown in red.

Figure 4

(a) The 3 × 3 × 2 AlN unit cells used in DFT calculations. The shaded region is magnified to show the atomic arrangements with (b) B interstitial; (c) Al interstitial; (d) N vacancy; and (e) Al vacancy. The point defect structures in (b)–(e) are relaxed from (a) using 3 × 3 × $3k$ points. The arrows mark the position of the defects.

Figure 5

DFT calculations for AlN in a 3 × 3 × 2 supercell: (a) Without point defects, (b) with single B interstitial, (c) with single Al interstitial, (d) with single N vacancy, and (e) with single Al vacancy. The defect states in the band gap are marked from A to J, and are summarized in Table 3. The Fermi levels are marked by black dashed lines.