Carrier transport by formation of two-dimensional hole gas in p-type Al0.1Ga0.9N/GaN superlattice for AlGaInN-based laser diode

We have investigated the electrical quality of Mg-doped p-type Al0.1Ga0.9N/GaN superlattice (SL) structures grown by metalorganic chemical vapor deposition (MOCVD) with different AlGaN and GaN thicknesses. The spatially averaged hole concentration of a p-Al0.1Ga0.9N/GaN superlattice structure was determined by the thickness of each layer in the SL. The hole concentration was significantly increased, above 1.0×1018 cm−3 by increasing the thickness of each layer in the SL due to the increase of the two-dimensional hole gas. The sheet resistance of a p-type Al0.1Ga0.9N/GaN superlattice structure used as the p-layer in an InGaN SQW laser diode (LD) was reduced by increasing the thicknesses of AlGaN or GaN layers in the SL. This is attributed to the increased hole concentration caused by two-dimensional hole gas at the interface between AlGaN and GaN. However, the series resistance of the AlGaInN-based LD structure increased with the thickness of the AlGaN layer. These results suggest that a thinner AlGaN layer in a p-type AlGaN/GaN superlattice structure can improve the operation of LDs.