Semipolar (202̅1) III-Nitride P-Down LEDs with in situ anneal to reduce the Mg memory effect

Abstract

P-down LEDs (PDLEDs) have the potential to open up new design schemes for III-nitride LEDs compared to conventional n-down LEDs (NDLEDs). For light emitters operating above 480nm, the PDLED design enables the epitaxial advantages of semipolar (202̅1) and gains the polarization benefits of semipolar (202̅1̅). Here, we investigated semipolar (202̅1) InGaN-based PDLEDs in terms of their photoluminescence (PL) spectra and compositional profile. Despite concerns of the Mg memory effect degrading PDLED performance due to Mg-related non-radiative recombination centers, the PL intensities were nearly identical between the NDLED and PDLEDs, which emitted at wavelengths centered near 500nm. Secondary ion mass spectrometry revealed that the Mg doping levels in the multiple quantum well (MQW) active region were comparable for each structure, with average values of 2.9×1018cm−3 for the NDLED and 1.8×1018cm−3 for the PDLED. Prior to growing the active region MQW, a 700°C in situ anneal was carried out to reduce the average Mg concentration in the PDLED MQW to 3.7×1017cm−3. Its hydrogen concentration remained at 5×1019cm−3 in the p-type GaN region, which suggests that hydrogen passivation occurs during the growth of subsequent epitaxial layers in ammonia.