Correlation between nanopipes formed from screw dislocations during homoepitaxial growth by metal-organic vapor-phase epitaxy and reverse leakage current in vertical p–n diodes on a free-standing GaN substrates

Abstract

We fabricated p−n diodes under different growth pressures on free-standing GaN substrates of the same quality and observed a noteworthy difference in the reverse leakage current. A large reverse leakage current was generated by nanopipes, which were formed from screw dislocations in the homoepitaxial layer. There were two types of screw dislocation observed in this study. The first type already existed in the substrate and the other was newly generated in the epilayer by the coalescence of edge and mixed dislocations. An increase in the growth pressure suppressed the transformation of screw dislocations into nanopipes, which led to a reduction in the reverse leakage current. To reduce the leakage current further, it is necessary to apply growth conditions that do not transform screw dislocation into nanopipes and to use a free-standing substrate without threading dislocations, that become nanopipes.

Correlation between structural properties and nonradiative recombination behaviors of threading dislocations in freestanding GaN substrates grown by hydride vapor phase epitaxy

“…26 It is also noted that the above double-core structure is different from an open-core nanopipe as reported by some groups. 20,33,50,51 The two dislocations show sharp and bright contrasts in the g/3g WBDF images, suggesting they are dislocations rather than the sidewalls of a nanopipe. The LACBED results and the etch pit image also support this conclusion.…”

“…The TDs have deleterious effects on the performance and lifetime of GaN-based devices through mechanisms such as carrier scattering, 9,10 carrier trapping via nonradiative recombination (NRR), [11][12][13][14][15][16] and paths for leakage current. [17][18][19][20][21][22] These different mechanisms are connected by the fact that dislocations act as one-dimensional (1D) charged defects that introduce electronic states into the energy gap. 14,[22][23][24] It is well accepted that the negative effects of dislocations on devices are strongly dependent on their Burgers vector and are susceptible to other dislocation characteristics, such as their line direction, 20 core structure, 20,22,[25][26][27] impurity gettering, 14,22 and surface morphology.…”

“…[17][18][19][20][21][22] These different mechanisms are connected by the fact that dislocations act as one-dimensional (1D) charged defects that introduce electronic states into the energy gap. 14,[22][23][24] It is well accepted that the negative effects of dislocations on devices are strongly dependent on their Burgers vector and are susceptible to other dislocation characteristics, such as their line direction, 20 core structure, 20,22,[25][26][27] impurity gettering, 14,22 and surface morphology. 21 However, there are large discrepancies in the literature regarding the relationship between the dislocation behavior and their structural properties.…”

“…28,29 Others found that the dislocations with the a component (TEDs and TMDs) act as NRR centers, 12,14 whereas the pure TSDs are inactive. 14 terms of leakage current pathways, most groups seem to agree that TSDs, especially those with an open-core, are responsible for the large leakage current under a reverse bias in Schottky barrier diodes (SBDs) 30 and vertical PN diodes, 18,20,22 even though the types of impurities that accumulate at the dislocations are different. When a Na-flux GaN substrate is used, the leakage current is strongly dependent on the growth sector at the initial stage of the Na-flux growth and has a positive correlation with the magnitude of the Burgers vectors, while the effects of oxygen impurities are implied.…”

Structural and Electrical Characterization of 2” Ammonothermal Free-Standing GaN Wafers. Progress toward Pilot Production

“…For example, Usami et al recently identified nanopipes formed from the coalescence of edge and mixed dislocations during epitaxial growth as leakage paths in vertical PN diodes. They accomplished this by superimposing emission microscope data with etch pit data and investigating the pits that coincided with the leakage spots using transmission electron microscopy [9]. In addition to having a low dislocation density, growing GaN devices on GaN substrates (GaN-on-GaN) allows vertical device architectures which have better thermal management, higher reliability, and high breakdown voltages using small devices as compared to lateral devices [10].…”