Study On The Optical Properties Of GaN Nanorods

In recent years, GaN based Ⅲ-nitride semiconductor materials have obtained the rapid development. Since they have unique optical and electrical properties, such as the wide direct band gap, which can be continuously turned from 0.7eV to 6.2eV, large exciton binding energy, high heat conductivity, etc., in comparison to the traditional materials, GaN based Ⅲ-nitride semiconductor materials have become the preferred materials for optoelectronic device applications. Nowadays, with the rapid development of the theory and technology, these researches and applications turn to a new direction, namely, nanomaterials and nanodevices. GaN based nanomaterials have significant quantum effect, so their optoelectronic properties will appear different new properties in comparison to the bulk materials, in addition, they will play a important role in the process of fabricating the nano-optoelectronic devices, thus, GaN based nanomaterials attract more and more attention, especially, GaN nanorod structures become the foreword and hotspot in the field of the GaN based nanomaterials science.This paper mainly focuses on studying the optical properties of GaN nanorods. Firstly, we compare the photoluminescence properties of GaN nanorods and as-grown planar by excitation power dependent photoluminescence (PL). Then, we investigate the quantum efficiency performance of the two samples when the excitation power is 0.5mW. The main results and conclusions are listed as follows:(1) There are three luminescence peaks in the PL speatral of GaN nanorods and planar. They are respectively band-edge peak (about 362nm), blue luminescence band (about 434nm), and yellow luminescence band (about 550nm). While, the origin of band-edge peak in the two samples are different. This can lead to the extent of increasing of the carrier proportion which participating in band-edge radiative recombination in nanorods is less than that of the excitation power 0.5mW, in comparison to that of excitation power 1mW.(2) In the test of excitation power range, GaN nanorods shows higher band-edge integrated PL intensity and lower blue luminescence as well as yellow luminescence integrated PL intensity, this suggests that GaN nanorods has better optical qualities.(3) With the excitation power increasing, the carrier proportion of participating in band-edge radiative recombination in GaN nanorods is larger than that of planar, correspondingly, the carrier proportion of participating in blue luminescence and yellow luminescence radiative recombination in GaN nanorods is smaller. These can be explained by the smaller point defects density in GaN nanorods. Meanwhile, this also explains the experimental phenomena, that the band-edge PL intensity in GaN nanorods changes from less to greater than yellow luminescence band, While, in planar, it’s still less than the yellow luminescence band.(4) In experiment, an enhancement of 12.2 times in the room temperature integrated PL intensity is observed from the GaN nanorods, in comparison to that of planar. This large integrated PL intensity enhancement of GaN nanorods can be attributed to the improvement of internal quantum efficiency (ηint) as well as light extraction efficiency.(5) We set up a new model, the ratio of ηint of GaN nanorods to that planar can be achieved. The calculated result turns out that the ηint of GaN nanorods is 2-3 times higher than the planar. Meanwhile, this model also proves that the traditional method for calculating ηint is not suitable for the nanorod structures.