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The dependence of contact resistivity on the carrier concentration for the non‐alloyed Pd contacts on p‐GaN and the temperature dependence measurements of sheet resistivity of p‐GaN suggest that carrier transport at the interface between the contact and the p‐GaN would be dominated by deep level defect band, rather than the valence band. Based on these results, in order to reduce the operating voltage of the InGaN laser diode (LD), we designed a p‐GaN : Mg contact layer, where the ohmic metals are contacted, and optimized the p‐GaN contact layer.

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GaN-based laser diodes for 405 nm high-power applications are demonstrated. By decreasing the Al concentration of n-cladding layers, the vertical divergence angle was reduced to <18° and the average COD level was increase to >300 mW. SUMMARYGaN-based blue-violet laser diodes (LDs) have attracted great interest as light sources for nextgeneration DVD applications [1][2][3][4]. In the near future, data capacity of dual-layer disc systems is expected to be more than 50 GB, which requires the output power of LDs to be higher than 100 mW. For this purpose, reduced vertical beam divergence angle and reliable high-power operation are of prime importance. Generally, the far field angle decreases as near field mode size increases. And, a high COD (catastrophic optical damage) level can be obtained by decreasing optical power density at the laser facet [2]. Therefore, small beam divergence angle and a high COD level can be achieved at the same time by the expansion of near field intensity at the facet. In this work, the refractive index of ncladding layers is increased by the control of Al concentration in AlGaN cladding materials in order to expand near field size. Based on this structure design, we achieved small vertical beam divergence angle of <18 degrees and a high COD level of >300 mW. LD samples were grown by metalorganic chemical vapor deposition (MOCVD) on c-plane sapphire substrates as described elsewhere [4]. The LEO (lateral epitaxial overgrowth) technique has been employed to decrease dislocation density of layers. The active layers consisted of three pairs of a 40 Å-thick InGaN well and a 100 Å-thick InGaN barrier, which was optimized to emit laser light near

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