| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
Y6, Misfit Dislocation Formation in Partially Strain-Relaxed (11-22) Semipolar InGaN |
| Author(s) |
Po Shan James Hsu, Erin C. Young, Alexey E. Romanov, Kenji Fujito, James S. Speck, Shuji Nakamura |
| On-Site Speaker (Planned) |
Po Shan James Hsu |
| Abstract Scope |
Semipolar orientations of wurtzite GaN are promising for long wavelength, high performance laser diodes (LDs) because of their reduced QCSE and higher theoretical gain. However, design of LD epitaxial structure on semipolar planes is unique in comparison to nonpolar and polar planes due to the possibility of forming stress-relieving misfit dislocations (MDs) at highly strained hetero-interface(s). The on-set of strain-relaxation in zinc-blende semiconductors occur via lateral glide of pre-existing threading dislocations (TDs). Such TD glide can occur similarly in semipolar wurtzite GaN as a result of the nonzero resolved shear stress on the inclined basal plane. The magnitude of the resolved shear stress is a function of the semipolar plane inclination angle with respect to the basal plane--which is a maximum for basal planes inclined ~45 degrees and decreases with increasing inclination angle. As a consequence, critical thicknesses for MD formation have been observed to vary for different semipolar orientations. In particular, the semipolar (11-22) plane (c-plane inclination ~58°) has been observed to have very low critical thickness in comparison to other semipolar planes such as the (20-21) plane (c-plane inclination ~75°) [1]. This is likely the key limiting factor in achieving stimulated emission in electrically-injected green (11-22) LDs. However, a better understanding of MD formation in semipolar GaN may provide lucrative opportunities in device design through proper dislocation control. In this work, we investigate strain-relaxation of (11-22) InGaN on GaN as a function of indium composition (fully coherent to partially relaxed). The samples were grown by metal-organic chemical vapor deposition (MOCVD) on nominally on-axis semipolar (11-22) free-standing GaN substrates. All samples were characterized by cathodoluminescence (CL) and X-ray diffraction (XRD).
Partially strain-relaxed (11-22) samples exhibited one-dimensional arrays of MDs along the crystallographic [1-100] direction when analyzed under panchromatic CL. The on-set of strain-relaxation detected by CL correlates well with Matthews Blakeslee's criterion for critical thickness--suggesting MDs are formed via TD glide. Further analysis under monochromatic CL at the substrate (365 nm) and InGaN peak, showed a single substrate TD associated with every MD. Symmetric reciprocal space maps (RSMs) along the [11-2-3] direction exhibited minimal detectable epi-layer tilt. This indicates a lower detection limit for strain-relaxation using X-ray diffraction, and is likely among the reasons why reported critical thicknesses for MD formation are higher than that calculated using Matthews Blakeslee's equilibrium criterion. |
| Proceedings Inclusion? |
Undecided |