Study On The Active Region Of V Pit-containing Gan-based Single Quantum Well Green LED Grown On Si Substrates

Compared with blue and red LEDs,the luminous efficiency of yellow and green LEDs is still lower,which is the bottleneck that restricts the development of high-quality full-spectrum LED lighting.To solve the problem of low luminous efficiency of green and yellow LEDs,it is necessary to recognize the luminous mechanism in the active region of LED.Compared with multi-quantum well LED,single-quantum well structure LED does not have the trouble of difference in luminous efficiency between different quantum well,which provides convenience for studying the luminous mechanism in the active region of LED.Therefore,in this dissertation,the active region of GaN based single quantum well green LED on Si substrate is taken as the main research object.The V-shaped pit is a defect in the quantum well active region of green LEDs.Any change of the active region will inevitably affect the characteristic of V-shaped pit.The V-shaped pit is also closely related to the photoelectric performance of LED devices.Therefore,the influence factors of V-shaped pit must be taken into account in the study of the quantum well active region of GaN based yellow and green LEDs.This dissertation mainly focuses on the structure and epitaxial growth parameters of active region of GaN based yellow and green LEDs on silicon substrate.The main contents and the obtained results are described as follows:The preparation method of high quality and high In component prelayer was obtained.The effects of different structures and different epitaxial growth methods on the In-incorporation,crystal quality and surface morphology of the prelayer were investigated.Both In-incorporation and the size of V-shaped pit of the prelayer were affected by the growth rate and indium gallium ratio of the prelayer.The faster the growth rate and higher indium gallium ratio is favorable for the more In-incorporation and smaller size of V-shaped pit.It was found that compared with the single-layer InGaN,the multi-layer InGaN/GaN had better surface morphology,and there would be no line-shaped defect caused by the connection of very small V-shaped pit.It was also observed that the surface morphology and crystal quality of the prelayer decreased when the growth rate of the prelayer increased from 0.2?/s to0.4?/s.Finally,the preparation method of high quality and high In component prelayer is:high indium gallium ratio,low growth rate and InGaN/GaN multi-layered structure.The forward and reverse leakage mechanism of GaN based yellow LED on Si substrate is illustrated.It was found that forward leakage was dominated by tunneling mechanism completely when the prelayer was grown at 850?.However,the forward leakage was dominated by tunneling mechanism together with the other mechanisms when the prelayer was grown at 880?.Reverse leakage is dominated by VRH mechanism?<250k?and P-F mechanism?>250k?.Within a certain range,the increase of v-shaped pit size and the increase of In component in the prelayer have an inhibitive effect on the reverse leakage behavior of devices dominated by P-F mechanism.In addition,it is also pointed out that the working voltage of LED devices is affected by their own series resistance and the area ratio of V-shaped pits in the active region.The experimental phenomenon that the working voltage of GaN-based green LEDs grown on Si substrate decreases with the number of quantum Wells within a certain range is reasonably explained on this basis.The reason for the luminous efficiency of GaN based single-quantum-well green LED on Si substrates decreases after the H₂ treatment during the GaN barrier growth while the forward and reverse leakage current decreases is explained.Experimental observation shows that EQE?525 nm,35 A/cm²?decreases by 5.3%after the H₂ treatment?including 2.5%H₂?.Both forward and reverse leakage currents decrease by an order of magnitude.The reasons for the above phenomenon are summarized as follows:The size of V-shape pits decreases after H₂ treatment.The holes tunneling barrier becomes thicker.It becomes more difficult for holes to inject into the quantum well.In addition,when introducing H₂ during the quantum barrier growth,H₂ etching would preferentially occur at V-shape pits,causing the significant indium loss.The blocking of the threading dislocations is more effective to reduce the leakage current.The effect of electron blocking layer?EBL?position on inhibiting the electron leakage of green InGaN/GaN single-quantum-well LEDs grown on Si substrates was proved by experiment and simulation.It was found that the position of the electron blocking layer was moved back 50 nm,the optical power of the device?500 nm,35A/cm²?increased 53%,the working voltage decreased by 0.1 V,and the electron leakage peak disappeared in the room temperature EL spectral under the high current density?80 A/cm²?.It is found that it is the p-GaN layer in front of AlGaN layer that really works for blocking the electron leakage as the position of the EBL moves back.The effective electron blocking potential barrier is increased by 91 meV and the hole transport potential barrier is reduced by 77 meV after the position of the EBL is moved back.In addition,the distribution of each layer material in the V-shaped pit can be changed after the position of the EBL is moved back,which influenced the hole transmission path.The hole tends to inject directly into the SQW from the c crystallographic plane.