| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
Y7, Observation of m-Plane Slip and Relaxation Orthogonal to the Projected c-Direction in (20-21) InGaN/GaN Partially Relaxed Layers |
| Author(s) |
Matthew Thomas Hardy, Feng Wu, Po Shan Hsu, Ingrid Koslow, Erin C. Young, James S. Speck, Steven P. DenBaars |
| On-Site Speaker (Planned) |
Matthew Thomas Hardy |
| Abstract Scope |
Despite recent progress, the performance of green light emitting diodes (LEDs) and laser diodes (LDs) is much lower than equivalent devices emitting in blue or violet regimes. Green emitting active regions are grown under very high strain – 3% for In<SUB>0.3</SUB>Ga<SUB>0.7</SUB>N, degrading crystal quality and leading to large piezoelectric induced electric fields in the quantum wells. Stress relaxation also limits the composition and thickness of InGaN waveguiding layers in LDs. <I>c</I>-plane slip has been observed on (11-22) and (20-21) semipolar orientations, which have significant resolved shear stress on the <I>c</I>-plane. An available stress relaxation mechanism which preserves the crystal quality of overlying layers opens up the possibility of growing relaxed InGaN buffers to reduce the strain in overlying InGaN layers. However, successful growth of such layers requires understanding the stress relaxation mechanism orthogonal to <I>c</I>-plane slip. A series of samples was grown by atmospheric MOCVD on free standing (20-21) GaN substrates. The layer composition was held constant at In<SUB>0.076</SUB>Ga<SUB>0.924</SUB>N and thickness was varied among 60, 90 110 and 150 nm. The samples were characterized by cathodeluminescence (CL), reciprocal space mapping (RSM) and TEM. CL images show the onset of <I>c</I>-plane slip in the 60 nm sample, in the form of short, low density misfit segments. At 90 nm the onset of formation of dark lines inclined relative to the projected <I>c</I>-direction is observed. These dark lines become more dense in the 110 nm sample and fully dense in the 150 nm sample. RSM measurements for the 150 nm sample were taken for 201 symmetric, 203 and 3-21 asymmetric reflections. The 201 RSM indicated a layer tilt of 0.51°, corresponding to a degree of relaxation of 0.33 assuming only <I>c</I>-plane slip. The 203 and 3-21 RSMs showed in-plane relaxation of Δq||/q|| = 0.018 and 0.013, respectively. Plan view TEM showed misfit lines parallel to <I>a</I> and inclined with respect to the projected <I>c</I>-direction. Cross sectional analysis confirmed the presence of misfit dislocations, all with a Burger’s vector of 1/3 <11-20>. The inclined lines observed in CL and plan view TEM appear to be parallel to [-2116]. This corresponds to the intersection of (20-21) and inclined <I>m</I>-planes, suggesting these lines are misfit dislocations generated by slip on inclined <I>m</I>-planes. As confirmed by the RSM measurements, such a system can relax stress in both orthogonal directions and appears to dominate once the Peierls force opposing slip on <I>m</I>-plane relative to <I>c</I>-plane is overcome by the lack of any alternative stress relaxation mechanism in the orthogonal direction. We have observed the progression of stress relaxation by slip on the <I>c</I>-plane to slip on the <I>m</I>-planes and shown that this new slip geometry is effective in relaxing stress orthogonal to <I>c</I>-plane slip. |
| Proceedings Inclusion? |
Undecided |