Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

Abstract

GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer.

Defects in Single Crystalline Ammonothermal Gallium Nitride

“…[43] Additionally, the formation of helical dislocations during heat treatment and epitaxy process has very recently been reported and associated with interaction of dislocations and point defects. [45] Here, we summarize recent progress in ammonothermal growth of GaN and consider the effects as-grown defects and dislocations have on the material properties. The second section presents an overview of the ammonothermal growth process and reviews the improvements done in the growth technology to reduce the level of impurities in the grown crystals.…”

“…[82,[84][85][86] Recently the formation of helical dislocations during heat treatment of ammonothermal GaN was associated with interaction of dislocations and vacancy defects. [45] The properties of gallium vacancies and their complexes with hydrogen (V Ga -H) have been calculated from first principles. [81,84,87] The isolated V Ga and V Ga complexed with one or two hydrogen atoms (V Ga -H 1,2 ) are acceptors and form defect states approximately 0.8 eV above the valence band, while V Ga -H 3 is neutral with a defect state close to the valence band.…”

The Impact of AlN Templates on Strain Relaxation Mechanisms during the MOVPE Growth of UVB‐LED Structures

“…Interestingly, this transformation seems to take place only when the number of TDs is low. [ 28,29 ] We suggest that in our samples this process appears in the already grown AlGaN layer with initially straight TD lines. A simultaneous action of a number of parameters must be responsible for this process: high growth temperatures, the presence of high compressive stress due to the overgrowth with AlGaN with a lower Al‐content, the presence of a relatively low TDD, which could accommodate this strain, and an excess of point defects, which are necessary for this climb process and transformation to the helical shape.…”

“…The formation of helical dislocations was rarely reported in group‐III nitrides, mostly either during coalescence of laterally overgrown GaN layers [ 28 ] or in ammonothermal GaN. [ 29 ] It was shown that in GaN with low TDDs TDs with initially vertical dislocation lines and a screw component of the Burgers vector can be transformed into helical dislocations at elevated temperatures. [ 29 ] Diffraction contrast analysis proved that in our sample the helical dislocations have both c ‐ and a ‐component of the Burgers vector.…”

“…[ 29 ] It was shown that in GaN with low TDDs TDs with initially vertical dislocation lines and a screw component of the Burgers vector can be transformed into helical dislocations at elevated temperatures. [ 29 ] Diffraction contrast analysis proved that in our sample the helical dislocations have both c ‐ and a ‐component of the Burgers vector. Vacancy absorption by straight dislocation lines was proposed to be the mechanism responsible for this transformation.…”