On carrier spillover in c-and m-plane InGaN Light Emitting Diodes

The internal quantum efficiency (IQE) and relative external quantum efficiency (EQE) in InGaN LEDs emitting at 400 nm with and without electron blocking layers (EBLs) on c-plane GaN and m-plane GaN were investigated in order to shed some light on any effect of polarization charge induced field on efficiency killer carrier spillover. Without an EBL the EQE values suffered considerably (by 80 %) for both orientations, which is clearly attributable to carrier spillover. Substantial carrier spillover in both polarities, therefore, suggests that the polarization charge is not the major factor in efficiency degradation observed, particularly at high injection levels. Furthermore, the m-plane variety with EBL did not show any discernable efficiency degradation up to a maximum current density of 2250 Acm(-2) employed while that on c-plane showed a reduction by similar to 40 %. In addition, IQE of m-plane LED structure determined from excitation power dependent photoluminescence was similar to 80 % compared to 50 % in c-plane LEDs under resonant and moderate excitation condition. This too is indicative of the superiority of m-plane LED structures, most probably due to relatively larger optical matrix elements for m-plane orientation.