Intrinsic luminescence and core structure of freshly introduced a-screw dislocations in n-GaN

Abstract

Dislocations introduced by the scratching or by the indentation of the basal and prismatic surfaces of low-ohmic unintentionally n-type doped GaN crystals were investigated by means of cathodoluminescence and transmission electron microscopy (TEM). A strong luminescence of straight segments of a-screw dislocations was observed in the temperature range of 70–420 K. The spectrum of dislocation related luminescence (DRL) consisted of a doublet of narrow lines red shifted by about 0.3 eV with respect to the band gap. TEM revealed dissociated character of the screw dislocations and the formation of extended nodes at their intersection. From the analysis of the DRL spectral doublet temperature, power and strain dependences DRL was ascribed to direct and indirect excitons bound by 1D quantum wells formed by partials and stacking fault (SF) ribbon of dissociated screw dislocation.

Asymmetry of the Atomic Core Structure of Dissociated a‐Screw Dislocation in GaN Probed by Polarization Optical Spectroscopy

“…The absence of dark contrasts of half‐loops in the basal plane indicates that the dislocation motion proceeded in a prismatic glide system only. Low‐temperature CL measurements confirmed that spectral properties of these dislocations were the same as the ones of dislocations introduced by scratching or indentation described earlier . Photoluminescence (PL) spectra of dislocation‐rich and dislocation‐free regions in the range from 3.5 eV (near band edge emission, NBE) to 3 eV coincided well with each other and are not shown here.…”

“…A dislocation‐related PL spectrum at 5 K consists of very narrow Lorenz‐type DRL H line at 3.167 eV with a full width at half maximum (FWHM) around 0.5–0.7 meV and of a broader DRL L line at 3.134 eV with FWHM of around 2.6–3 meV. The energy separation between DRL H and DRL L peaks is about 33 meV, which coincides well with the CL‐spectra value at temperatures higher than 70 K . PL intensity of DRL H at 5 K was 5–10 times higher than the intensity of DRL L .…”

“…Recently, it was reported that freshly introduced straight segments of a‐screw dislocations in low‐ohmic unintentionally doped n‐type GaN crystals exhibited a strong intrinsic UV‐luminescence that persisted above room temperature. A DRL spectrum of an individual dislocation in low‐ohmic GaN consisted of a doublet of narrow lines with high‐energy (denoted as DRL H ) and low‐energy (denoted as DRL L ) components separated by 30 meV and redshifted as a whole by about 0.3 eV with respect to the bandgap.…”

“…Transmission electron microscopy (TEM) revealed dissociated character of the a‐screw dislocation cores containing two 30° Shockley partial dislocations bounding the SF ribbon. From the analysis of the DRL spectral doublet temperature, power and strain dependences DRL H and DRL L lines were ascribed, respectively, to spatially direct and indirect excitons bound by 1D quantum wells formed by the partials and SF ribbon of dissociated screw dislocation …”

“…Two kinds of the dislocated samples were under study. The first one was locally plastically deformed samples created by the scratching or indentation of (0001) surface at room temperature that were similar or the same as used in previous studies . The polarization luminescent study of such samples revealed a strong anisotropy for both DRL components.…”