Threading edge dislocation arrays in epitaxial GaN: Formation, model and thermodynamics

• We observed and considered the distribution of dislocations in MOCVD-grown Gallium Nitride.
• The origin of edge-type dislocation arrays is attributed to grain coalescence.
• The distribution of dislocations is quantitatively modeled by thermodynamic theory.
• The phase transition of GaN from polycrystal to monocrystal during the two-step epitaxial method is explained.

The arrays of edge threading dislocations (TD) have been observed in highly dislocated GaN film grown on Al2O3(0001) substrate. There are three kinds of arrays including straight-row, partial-circle and full-circle arrays. A theoretical model derived from the thermodynamics of grains evolution during the GaN recrystallization was used to explain the appearance of these arrays and the statistical distribution of edge TDs. Both the theoretical and experimental results show a Weibull distribution of edge TDs. It is concluded that in crystalline GaN epitaxial films, the edge TD arrays originate from grain coalescence after the recrystallization.