Effect of hydrogen treatment temperature on the properties of InGaN/GaN multiple quantum wells

Effect of Hydrogen Treatment on Photoluminescence and Morphology of InGaN Multiple Quantum Wells

In this paper, the photoluminescence (PL) properties and surface morphology of InGaN/GaN multiple quantum well (MQW) structures with the hydrogen (H₂) heat treatment of InGaN are investigated to elucidate the effect of hydrogen on the structure and surface of the MQWs. The experimental results show that the H₂ heat treatment on the as-grown MQWs may lead to the decomposition of InGaN and the formation of inhomogeneous In clusters. The atomic force microscope (AFM) study indicates that although the surface roughness of the uncapped samples increases after H₂ treatment, the V-defects are suppressed. Moreover, the luminescence efficiency of the MQWs can be effectively improved by growing a GaN cap layer with an appropriate thickness on the top of the MQWs, which can reduce the effects of the H₂ atmosphere and high temperature on the MQWs. In addition, a morphologic transformation from step bunching to shallow steps occurs and a much smoother surface can be obtained when a thicker cap layer is adopted.

Anomalous Temperature Dependence of Photoluminescence Caused by Non-Equilibrium Distributed Carriers in InGaN/(In)GaN Multiple Quantum Wells

An increase of integrated photoluminescence (PL) intensity has been observed in a GaN-based multiple quantum wells (MQWs) sample. The integrated intensity of TDPL spectra forms an anomalous variation: it decreases from 30 to 100 K, then increases abnormally from 100 to 140 K and decreases again when temperature is beyond 140 K. The increased intensity is attributed to the electrons and holes whose distribution are spatial non-equilibrium distributed participated in the radiative recombination process and the quantum barrier layers are demonstrated to be the source of non-equilibrium distributed carriers. The temperature dependence of this kind of spatial non-equilibrium carriers’ dynamics is very different from that of equilibrium carriers, resulting in the increased emission efficiency which only occurs from 100 to 140 K. Moreover, the luminescence efficiency of MQWs with non-equilibrium carriers is much higher than that without non-equilibrium carriers, indicating the high luminescence efficiency of GaN-based LEDs may be caused by the non-equilibrium distributed carriers. Furthermore, a comparison analysis of MQWs sample with and without hydrogen treatment further demonstrates that the better quantum well is one of the key factors of this anomalous phenomenon.