Internal quantum efficiency of m-plane InGaN on Si and GaN

High brightness InGaN light emitting diodes (LEDs) require high quantum efficiency and its retention at high injection levels. The efficiency drop at a high injection levels in InGaN light emitting diodes (LEDs) has been attributed, e.g. to polarization field on polar c-plane InGaN and the heavy effective hole mass which impedes high hole densities and transport in the active quantum wells. In this study, we carried out a comparative investigation of the internal quantum efficiency (IQE) of InGaN active region in LED structures using resonant optical excitation for layers with polar (0001) orientation on c -plane sapphire, and nonpolar (1-100) m -plane orientation, the latter on specially patterned Si and on m -plane bulk GaN. Analysis of the resonant photoluminescence (PL) intensity as a function of the excitation power indicate that at comparable generated carrier concentrations the IQE of the m -plane InGaN on Si is approximately a factor of 2 higher than that of the highly optimized c -plane layer. At the highest laser excitation level employed (corresponding carrier concentration n ~ 1.2 x 10 18 cm -3 ), the m -plane LED structure on Si has an IQE value of approximately 65%. We believe that the m -plane would remain inherently advantageous, particularly at high electrical injection levels, even with respect to highly optimized c-plane varieties. The observations could be attributed to the lack of polarization induced field and the predicted increased optical matrix elements.