Effects Of The Structure Near Quantum Wells On Photoelectric Properties Of GaN Based LEDs On Silicon Substrate

Silicon substrate GaN based LEDs are attracting more and more attention for its advantages, such as, lower manufacturing cost, simpler package process and higher reliability. The first successful development of practical level of blue LED was made in 2004. After ten yeas in 2013, the photoelectric performance of LEDs had been comparable to the mainstream technology route.The manufacturing technology of GaN based LED on silicon substrate in this labhas been mature. Until now, optimized epitaxial platform for LED on silicon has been gradually established, including, the quantity of quantum wells, total thickness of well and barrier, MQWs doping, n-type doping, p-type doping and other main structure characteristics.As the active region,effect of strcture near quantum wells is vital on the photoelectric performance of LEDs. Based on previous research in our lab, this paper did some further optimization of the structure near quantum wells to improve the performance of LEDs. Here, the structure near quantum wells conclude cap layer in barrier, low temperature GaN preparation layer, p-AlGaN electron blocking layer and p-type layer. The conclusions are as follows:1.The effect of cap layer thickness in quantum barrier on the optoelectronic properties of blue LEDs isinvestigated. It is found the sample with10? cap obtains uniform indium component and clear interface. Under operating current density, 10? sample has higher light output power, external quantum efficiency and lower working voltage. In addition, the peak width at half height(HW) is wider. The improve on efficiency and voltage is due to the promotion of interface between barrier and well. It plays a better role on carrier leakage and ohmic contact. Therefore, we consider 10? cap layer is suitable to improve the luminous efficiency and overall photoelectric performance.2.Three different thickness of low temperature GaN epitaxial film are grown to study the effect of V-pits size on the optoelectronic properties of blue LEDs. With the increasing of V-pits size, epitaxial film contains higher In components, smaller strain, higher relaxation. Under operating current density, the light power and external quantum efficiency is higher. And the efficiency droop is improved. In addition, the working voltage and leakage current decrease. It benefits from larger V-pits, which screens dislocation and increases the injection of holes. At the same time, we noticed that the leakage current tends to increasing with larger V-pits.Itis due to the competitionbetween screening dislocations and new generated defects. Aging tests on the samples indicate silicon substrate GaN based LEDs has high reliability and suitable selection of V-pits size could further relieve the luminance decrease in aging.3. The effect of p-AlGaN EBL thickness on the performance of InGaN/GaN multiple quantum wells(MQWs) green light-emitting diodes(LEDs) was investigated. It was observed that increasing the thickness of p-AlGaN EBL could reduce the leakage current and improve the efficiency of green LEDs with large V-pits. It is proposed that the increasing of EBL thickness leads to a thicker p-AlGaN on the sidewalls of V-pits, which provides thicker energy barrier and consequently screens dislocations more effectively. The leakage current(at-5V)of LEDs with 40 nm EBL is about an order magnitude lower than that of LEDs with 20 nm EBL. With the increase of EBL thickness, at low current densities, the external quantum efficiency(EQE) decreases firstly and increases afterwards, which could be attributed to the competition between enhancement of radiative recombination rate and reduction of hole injection efficiency. At operating current density, there is positive correlation between EQE and the thickness of EBL. It is accredited to the improved electron confinement in the active region by preventing electrons overflowing to the p-type layer. Meanwhile, the efficiency droop is obviously suppressed when the thickness of EBL increase from 20 nm to 40 nm. However, further increasing the thickness of EBL may deteriorate the EQE and efficiency droop.4.We study the effect of P-type GaN thickness on the optoelectronic properties of blue LEDs. Under operating current density, sample with thinner P-type layer has higher light output power, luminous efficiency and smaller working voltage. At the same time, the reverse leakage is also improved. It is mainly due to the thinner p-type layer is more advantageous to hole injection, resulting in increasing radiative recombination and decreasing series resistance.