The dissociation of (a+c) misfit dislocations at the InGaN/GaN interface

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Heterostructures

Background:

• Hexagonal materials commonly exhibit (a+c) dislocations dissociating into partial dislocations.
• Relaxed InGaN buffer layers are essential for depositing high indium content structures.
• Understanding misfit (a+c) dislocation dissociation at the InGaN/GaN interface is key for controlling nucleation and glide.

Purpose of the Study:

• Investigate the dissociation mechanism of misfit (a+c) dislocations in plastically relaxed InGaN layers on GaN substrates.
• Characterize the structure and behavior of these dissociated dislocations.
• Elucidate the role of stress in the dissociation process.

Main Methods:

• High-resolution microscopy to observe dislocation networks and dissociation.
• Atomistic simulations to model the core structure of dissociated edge (a+c) dislocations.
• Analysis of dislocation networks at the InGaN/GaN interface.

Main Results:

• A trigonal network of (a+c) dislocations was observed at the InGaN/GaN interface, rotated 3° from <100> directions.
• Dislocations were found to dissociate into two Frank-Shockley 1/6<203> partial dislocations with an I1 stacking fault.
• Atomistic simulations revealed a 3/5-atom ring structure for the partial dislocation cores.
• The separation of partial dislocations suggests climb, potentially induced by mismatch stress.

Conclusions:

• The dissociation of misfit (a+c) dislocations in InGaN/GaN involves Frank-Shockley partials and I1 stacking faults.
• Dislocation climb, likely stress-induced, plays a role in the observed partial dislocation separation.
• This study provides critical insights into the mechanisms governing dislocation behavior in nitride semiconductors, impacting device performance.