Study On Optical-electrical Properties Of GaN-based LED

GaN and its alloys compound (AlGaN, InGaN) have been widely used in microelectronic devices (such as LEDs, LDs, HEMT), due to the strong chemical stability and tunable band gap characteristics. Particularly in the field of LED lighting, GaN is playing an irreplaceable role. High crystalline quality of LED chips have been prepared by metal organic chemical vapor deposition (Metal-Organic Chemical Deposition, referred to as MOCVD), but the internal quantum efficiency of GaN-based LED is still relatively low. Therefore, it is particularly important to understand the mechanism of carrier recombination in light emitting diode, optimize the structure of LED and improve the LED efficiency.In this paper, the PL, EL, Ⅰ-Ⅴ and Raman testing methods were used to investigate the influence of InGaN/GaN quasi-superlattice underlayer and low temperature p-GaN insetion layer on the optical-electrical characteristics of GaN-based LED. We try to explain the influence mechanism of InGaN/GaN quasi-superlattice underlayer and low temperature p-GaN insetion layer on the optical-electrical characteristics of GaN-based LED by studing the temperature dependent and excitation power dependent of PL and EL test. The main contents of the article include the following aspects:(1). The influence of InGaN/GaN quasi-superlattice (QSL) underlying buffer layer on the temperature dependent of the two samples is studied. The result shows that sample with InGaN/GaN quasi-superlattice (QSL) underlying buffer layer shows a smaller blue-shift of the PL peak energy. This is because the stress in MQWs is released after inserting the InGaN/GaN quasi-superlattice (QSL) underlying buffer layer;(2).The influence of InGaN/GaN quasi-superlattice (QSL) underlying buffer layer on the excitation power dependent of the two samples is studied. The result shows that the composition fluctuation or phase separation of the InGaN well layers is more obvious after inserting the QSL. This is because the strain is released and the strain release facilitates the slight composition fluctuation, or phase separation, of the InGaN well layers;(3).The PL intensity of the two samples, with and without an InGaN/GaN quasi-superlattice (QSL) underlying buffer layer, were investigated. The results show that inserting a QSL between the n-GaN and MQWs can improve the PL intensity. This is because inserting a QSL between the n-GaN and MQWs can release the strain in the MQW region and facilitates the slight composition fluctuation or phase separation of the InGaN well layers;(4).The Ⅰ-Ⅴ results of the two samples with and without low temperature p-GaN insertion layer are studied. At room temperature, the forward voltages are reduced after inserting a low temperature p-GaN layer. This is due to the significantly improvement of hole injection efficiency after inserting the low temperature p-GaN layer;(5).The influence of low temperature p-GaN on In component in quantum well is studied. Compared the obvious differences in EL of the two samples, the PL of two samples nearly has no difference. This is due to the suppression of low temperature p-GaN layer on In diffusion in the last quantum wells;(6).The influence of low temperature p-GaN layer on the excitation power dependent of the two samples is studied. After inserting a low temperature p-GaN layer, the diffusion of In component is suppressed and QCSE is enhanced.As the excitation power increases, the peak energy rise rapidly;(7).The EQE of the samples with and without low temperature p-GaN layer are compared. The results show that the EQE of sample is still large and the "efficiency droop" is not obvious in a large current after inserting a low temperature p-GaN layer. This significant improvement in "efficiency droop" behavior can be attributed to the enhancement of hole injection efficiency. Therefore, the designed low temperature p-GaN insertion layer can be a useful mean to alleviate "efficiency droop" behavior;(8).APSYS simulation program is carried out to simulate the band diagrams, carrier distributions, and radiative recombination in the sample with and without low temperature p-GaN layer, which also are compared with the experimental data. The results show that the simulation data are basically as same as the experimental data.