Influence of interface structure in the active region on photoluminescence in InGaN/GaN quantum wells

Two different InGaN/GaN multiple quantum wells (MQWs) were prepared. They contain AlN low-temperature interlayers (LTILs) between the GaN barrier and InGaN well layers, one with a trapezoidal InGaN QW and the other with a quasi-trapezoidal InGaN QW without terminal In composition gradient region (ICGR). Meanwhile, their photoluminescence (PL) spectra were acquired and their dependences on the excitation power and temperature were studied. These measurements reveal a smaller quantum-confined Stark effect, a stronger carrier localization effect, and a higher internal quantum efficiency of the quasi-trapezoidal QWs compared with that of the trapezoidal QWs. This phenomenon is a result of the fact that: the characteristic structure of the quasi-trapezoidal InGaN QWs, cannot only reduce strain in the active region due to effective strain-compensated effect of the AlN LTILs, but also avoid diffusion of In atoms from the high In region containing In-rich clusters into the terminal ICGR due to the lack of the terminal ICGRs. The former reduces the piezoelectric polarization fields induced by the lattice mismatch between well and barrier layers, the latter suppresses the degradation of the In-rich clusters and the generation of non-radiative centers.