Articles you may be interested inSuppression of metastable-phase inclusion in N-polar ( 000 1 ¯ ) InGaN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 106, 222102 (2015); 10.1063/1.4922131 Morphological, structural, and emission characterization of trench defects in InGaN/GaN quantum well structures Appl. Phys. Lett. 101, 212107 (2012); 10.1063/1.4768291 Investigation of V-Defects and embedded inclusions in InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition on (0001) sapphire Appl. Phys. Lett. 83, 33 (2003); 10.1063/1.1588370 Dislocation behavior in InGaN/GaN multi-quantum-well structure grown by metalorganic chemical vapor deposition Appl.Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells grown by metalorganic chemical vapor depositionThe morphological evolution of InGaN/GaN multiple-quantum wells ͑MQWs͒ grown by metalorganic chemical vapor deposition has been examined by atomic force microscopy and cross-sectional transmission electron microscopy. We have determined that GaN barrier growth at low temperature ͑ϳ800°C͒ in a H 2 -free environment results in a microstructure that consists of not only V-defects, but also inclusions embedded within V-defects that originate at the first InGaN-to-GaN growth interface. Propagation of the inclusions results in progressive deterioration of the surface morphology and reduced MQW thermal stability as quantum-well periods are added. Raising the GaN barrier growth temperature to 900°C or adding H 2 suppresses inclusion propagation entirely and preserves two-dimensional step-flow growth mode, resulting in superior morphology and higher thermal stability.

Morphological evolution of InGaN/GaN quantum-well heterostructures grown by metalorganic chemical vapor deposition

On Si-implanted n-type GaN, a nonalloyed Ti/Al metallization has been found to form an Ohmic contact that has a specific contact resistance as low as 1.0×10−5 Ω cm2. The Ohmic character is believed to be caused by the 1120 °C implant activation anneal which generates nitrogen vacancies that leave the surface heavily n type. This theory is indirectly confirmed on unimplanted n-type GaN by comparing the rc of nonalloyed Ti/Al on unannealed GaN with that of nonalloyed Ti/Al on 1120 °C annealed GaN. The former has rectifying electrical characteristics, while the latter forms an Ohmic contact with an rc=1.3×10−3 Ω cm2.

The presence of oxygen in the annealing environment can exhibit a strong influence on the activation of p-GaN, as demonstrated by experiments described in this letter. We activated p-GaN at 600–900 °C in four environments: ultrahigh purity (UHP) N2 gettered to remove residual O2, UHP N2 without gettering, 99.5% UHP N2/0.5% UHP O2, and 90% UHP N2/10% UHP O2. The resistivity of the p-GaN was lowest when O2 was intentionally introduced during activation and was highest when extra care was taken to getter residual O2 from the annealing gas. The experiments also demonstrate that unintentionally incorporated O2 can be at high enough levels to influence the activation process.

We have measured high spatial/depth resolution (∼2–3 μm) thermal conductivity (κ) at 300 K of both fully and partially coalesced GaN/sapphire (0001) samples fabricated by lateral epitaxial overgrowth. On the fully coalesced sample we found 1.86W/cm K<κ<2.05 W/cm K over a distance of approximately 50 μm. One of the partially coalesced samples had 2.00 W/cm K<κ<2.10 W/cm K on the overgrown regions, as identified by atomic force microscopy imaging. These latter results are the highest thermal conductivity values reported on GaN material. A correlation between low threading dislocation density and high thermal conductivity values was established.