Comparison between Polar (0001) and Semipolar (1122) Nitride Blue-Green Light-Emitting Diodes Grown on c- and m-Plane Sapphire Substrates

摘要

We present a comparative study of semipolar (1122) and polar (0001) (ln,Ga)N/GaN light emitting diodes grown simultaneously under equal conditions by metalorganic vapor deposition. These structures are grown on 2-in. GaN templates with two different (1122) and (0001) orientations. The templates were formerly obtained by MOCVD, on (1010) m-plane and (0001) c-plane sapphire substrates. The semipolar quantum wells exhibit a 30% higher indium content compared to the polar quantum wells. This was confirmed by complementary X-ray diffraction and energy dispersive X-ray spectroscopy measurements on thick (～60nm) InGaN layers grown on (1122) and (0001) GaN templates. The results of electroluminescence and photocurrent show that the emission of semipolar QWs is strongly red-shifted with respect to the band edge. This large Stokes' shift is attributed to carrier localization at potential minima induced by indium composition fluctuations. A strong blueshift under forward DC injection is observed for the semipolar (Ga,ln)N diodes. Since a reduced piezoelectric field is expected in the semipolar diodes, the observed blueshift is mainly due to carrier filling of the localized states.