Influence of in fraction on the optical properties of InGaN/GaN blue light-emitting diodes

Scanning transmission electron microscopy (STEM) and temperature dependent photoluminescence (PL) measurement are used to study the influence of In fraction on the optical properties of InGaN/ GaN blue light-emitting diode (LED). STEM results reveal that both of two samples have the same quantum-well structure. Low-temperature dependence of PL shows that the peak energy of one sample with lower In fraction exhibites a classical S type (Red-Blue-Red) with increasing temperature. Currently it is recommended that the blue shift of peak energy (with increasing temperature) is mainly due to exciton recombination, which is caused by inhomogeneous In distribution. However, the sample with higher In fraction doesn't show any blue shift about the peak energy. This unnormal phenomenon can be mainly attributed to the large thermal barrier caused by potential fluctuation of high In composition, which prohibits carriers transition from strong localized state into weak localized state (this process can cause blue shift of energy). Meanwhile, band filling process of carriers becomes prominent in the role of energy blue shift from 160 K to 300 K, this can be attributed to the more obvious quantum confined effect in higher In fraction sample, compared with lower In fraction, resulting in smaller average red shift of peak energy.