Invited Paper EM-ThM9
Heteroepitaxial Lattice Mismatch Stress Relaxation in Nonpolar and Semipolar GaN by Dislocation Glide

Thursday, November 1, 2012, 10:40 am, Room 009

Light emitting devices, namely LEDs and laser diodes, grown on c-plane GaN suffer from large internal electric fields due to discontinuities in spontaneous and piezoelectric polarization effects which cause charge separation between holes and electrons in quantum wells and limits the radiative recombination efficiency. Nonpolar GaN devices, such as in the m-plane {1100}, are free from polarization related electric fields since the polar c-axis is parallel to any heterointerfaces. Semipolar GaN-based devices have reduced electric fields.

Nonpolar and semipolar nitride epitaxial layers have other striking differences from c-plane. Namely, in conventional c-plane GaN heteroepitaxy, there is no shear stress on the easiest slip plane – the (0001) or basal plane and the next easiest slip plane – the prismatic {1100} m-plane. Epitaxy of mismatched layers on nonpolar and semipolar GaN, there are significant shear stresses in the inclined m-planes and on the inclined c-plane. Significant lattice mismatch-related stresses can be relieved by misfit dislocation formation via threading dislocation glide.

In this talk, we present the progress in developing high quality relaxed semipolar templates. The predominant relaxation in semipolar InGaN on GaN or AlGaN on GaN, in orientations such as (1122) or (2021), proceeds via threading dislocation glide on the inclined basal plane, followed in many cases by prismatic slip [1]. Since semipolar GaN has only one (0001) plane, plastic relaxation results in crystallographic tilt which can easily be measured in on-axis x-ray rocking curves or reciprocal space maps and can be directly used to quantify the extent of plastic strain relaxation [2]. The initial misfit stress relaxation occurs by glide of pre-existing threading dislocations [3,4] at a thickness slightly greater than the Matthews-Blakeslee critical thickness; the development of pseudomorphoric InGaN and AlGaN semipolar buffer layers via dislocation strain relaxation [5,6,7]; blue (1122) LDs in relaxed buffer layers [8]; green LEDs on relaxed buffer layers [9].

[1] F. Wu et al., Appl. Phys. Lett 99, 251909 (2011).

[2] E.C. Young et al. Appl. Phys. Express 3, 011004 (2010).

[3] E.C. Young et al. Appl. Phys. Express 3, 111002 (2010).

[4] P.S. Hsu et al., Appl. Phys. Lett. 99, 081912 (2011).

[5] F. Wu et al. J. Appl. Phys. 109, 033505 (2011)

[6] A.E. Romanov et al., J. Appl. Phys. 109, 103522 (2011).

[7] E.C. Young et al. Appl. Phys. Express, 4, 061001 (2011).

[8] P.S. Hsu et al. Appl. Phys. Lett. 100, 021104 (2012).

[9] I. Koslow et al. submitted for publication (2012).