Atomic force microscopy analysis of cleaved facets in III-nitride laser diodes grown on free-standing GaN substrates

Abstract

The cleaved {11¯00} mirror facets of III-nitride ridge waveguide laser diodes grown on free-standing GaN substrates have been characterized using atomic force microscopy. The measurements indicate that the exposed facets are atomically smooth and therefore they have a much lower roughness than has been reported for cleaved surfaces of III-nitride heterostructures grown on other substrates. Individual heterostructure layers—including InGaN quantum wells only 3nm thick—could be identified from small variations in the height of the exposed surface. These variations are attributed primarily to the partial relaxation of strained layers at the free surface.

100 μm-Cavity GaN-Based Edge Emitting Laser Diodes by the Automatic Cleavage Technique Using GaN-on-Si Epitaxial Lateral Overgrowth

“…Each stripe was aligned parallel to the [11̅00] direction as mentioned above. This configuration made it possible to use the m -plane most favorable to cleaving in crystal GaN as a facet. − This was also favorable for obtaining a short cavity because the distance for complete separation was much shorter than that of a typical continuous film wafer. We applied the inherent stress in the stripes due to the difference in the thermal expansion coefficient between Si and GaN so that only the stripe portion was cleaved, while the Si substrate remained intact.…”

Long lifetime cw InGaN laser diodes by molecular beam epitaxy

“…The substrates are compatible with the current industry trend and are available as 2" wafers. They also enable high-quality cleaved facets [15], higher thermal conductivity and backside ncontacts. Molybdenum is deposited before growth on the backside of the substrates, allowing them to be radiatively heated to the required growth temperature.…”

“…A cleaved facet is shown in Fig. 2, and cross-sectional AFM measurements show that the cleaved facets are usually atomically flat over at least tens of square micrometers [15]. On some of the laser bars highly reflective coatings consisting of four pairs of quarter-wave Si 3 N 4 /SiO 2 were applied to the facets after cleaving.…”