Free-standing zinc-blende (cubic) GaN substrates grown by a molecular beam epitaxy process

In this paper bulk, free-standing, zinc-blende (cubic) GaN wafers grown by plasma-assisted molecular beam epitaxy (PA-MBE) are described. GaN layers of up to 60 microns in thickness have been grown. Characterisation measurements confirm the cubic nature of the GaN crystals and show that the fraction of hexagonal material present is not more than ∼10%. Cubic (001)GaN does not exhibit the spontaneous and piezoelectric polarization effects associated with (0001) c-axis wurtzite GaN. Free standing GaN wafers grown by PA-MBE make ideal lattice-matched substrates for the growth of cubic GaN-based structures for optoelectronic devices, and high power and high frequency electronic applications.