Nitride-based laser diodes using thick n-AlGaN layers
We obtained 1 µm crack-free AlGaN layers up to an AlN molar fraction of 0.4 by growing directly on low-temperature-deposited buffer layers. The buffer 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 µm 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 threshold current of the laser diode is about 230 mA, which is comparable to or better than that of our laser diodes with the conventional GaN-based structure.