Nitride-based laser diodes using thick n-AlGaN layers

We obtained 1 mu m crack-free AlGaN layers up to an AlN molar fraction of 0 .4 by growing directly on low-temperature-deposited buffer layers. The buff er layer is effective for growing AlGaN layers without the stress caused by the lattice mismatch, We also demonstrated nitride-based laser diodes with such a 1 mu m crack-free n-AlGaN cladding layer/n-AlGaN contact layer/low- temperature-deposited buffer layer/sapphire structure, which showed a clear single spot in a far field pattern. The AlGaN-based structure can suppress optical leakage from the waveguide region to the underlying layer. The thr eshold current of the laser diode is about 230 mA, which is comparable to o r better than that of our laser diodes with the conventional GaN-based stru cture.