Recombination of Shockley partial dislocations by electron beam irradiation in wurtzite GaN

Abstract

Dissociated a-type screw dislocations in gallium nitride, comprising pairs of 30° Shockley partial dislocations separated by I2 basal stacking faults, were observed by aberration-corrected high resolution transmission electron microscopy (HRTEM). HRTEM image simulations, in conjunction with density functional theory calculations, led to the identification of the core structures of the Shockley partials. Both partials were found to belong to the glide set rather than the shuffle one, while the core with gallium polarity is reconstructed, but the one with nitrogen polarity is not. During in situ irradiation by the electron beam, the I2 stacking fault ribbon was found to shrink, ultimately leading to a remerging of the two partials. This reversal of the dissociation reaction was attributed to recombination enhanced dislocation glide, whereby the Shockley partial with nitrogen polarity was identified to be the mobile one. A possible model explaining this mobility is proposed comprising a local modification of the dislocation's electronic structure due to the presence of nitrogen vacancies at its core.

Sequential plan-view imaging of sub-surface structures in the transmission electron microscope

“…For example, hydrogen was found to be incorporated into Ti samples prepared using conventional room temperature FIB (using Ga ion or Xe plasma source) or electropolishing [32]. As another example, dissociated dislocations were found in GaN foils as a result of strain relaxation occurring during mechanical sample preparation [33].…”

Stacking Fault Manifolds and Structural Configurations of Partial Dislocations in InGaN Epilayers

“…Models of m-line Shockley PD core structures and rotational projected similarities to a-line PDs (SP and DP denote single and double period, respectively). [35,41] m-line…”

“…Other works also support the REDG phenomenon in association with point defects in GaN, and the participation of I 2 BSFs in device degradation processes. [43,44] In our previous work, [35] dissociated 1/3<21 1 0> lattice dislocations were found to adopt curved configurations, being predominantly screw along <21 1 0> a-lines with short <0110> m-line segments. Dissociation of 1/3<21 1 0> edge dislocations along m-lines into pairs of Shockley PDs has been observed in wurtzite-structured ZnO.…”

“…When a counterclockwise rotation is applied to the 60 -glide-N PD (Figure 8c), it exhibits a projected core similar to that of the 90 -glide-N double-period PD (Figure 8d). [35,41] The screw PD looks like a single-period 30 -glide-Ga PD when rotated clockwise (Figures 8e,f ). Such similarities appear for all cores, and these resemblances are summarized in Table 1.…”

“…carrier injection through the phenomenon of recombinationenhanced dislocation glide (REDG). [35] This could be promoted by a modification of their electronic structure due to the segregation of nitrogen vacancies. Other works also support the REDG phenomenon in association with point defects in GaN, and the participation of I 2 BSFs in device degradation processes.…”