Effects Of P-type Doping And The Quantum Wells' Structure On Photoelectric Properties Of GaN Based LED

With the progress of GaN-based material epitaxial growth and related device preparation fabrication,InGaN/GaN based MQWs LEDs have shown great potential in the field of solid-state lighting,therefore getting wide attention.However,due to the difficulty of p-type doping and the difference in electron and hole transport properties,the carrier concentration and their distribution in the active region are extremely mismatched,which restrict the development and application of high bright high power LEDs.Thus,it is necessary to solve above problems.In this dissertation,we study the GaN-based LED on Si substrate grown by MOCVD.Based on the previous research work,to improve the photoelectric properties of InGaN/GaN-based LEDs,we optimize p-type doping of p-AlGaN electron blocking layer and the structure of quantum wells and draw the following main conclusions:1?The effects of Mg-preflow of p-AlGaN EBL on Mg concentration of p-AlGaN in blue?green?yellow LEDs were investigated,respectively.It was found that Mg-preflow of p-AlGaN could increase the Mg concentration by reducing the effect of memory effect of Mg.2?The effect of Mg-preflow of p-AlGaN EBL on photoelectric properties of blue LEDs was studied.Compared with the sample without Mg-preflow,the sample with Mg-preflow in p-AlGaN had higher EQE at room temperature and less serious IQE collapse,which resulted from the higher Mg concentration in EBL.Higher Mg concentration in EBL can make more holes being ionized and enhance the holes injection efficiency,which obtained the better carrier symmetry.3?The effect of Mg-preflow of p-AlGaN EBL on photoelectric properties of green and yellow LEDs was studied.It was observed that the dependence of peak wavelength and FWHM on the current density was the same as that of blue LEDs.However,the reduced EQE at room temperature and enhanced EQE at 100 K were obtained in the green and yellow LEDs with Mg-preflow of p-AlGaN.In the Mg-preflow samples,there were two factors that could have significant effects on the EQE.One was the increased holes concentration in the p-AlGaN,which could be beneficial to the improvement of EQE.Another was lighting mainly came from the quantum wells close to the p-GaN,which had poorer crystal quality,due to the hole mainly conducted by sidewall of V-shaped pits.For green and yellow LEDs with higher In content compared with blue LEDs,a more serious lattice mismatch occurs in the quantum wells,and there exists much more defects due to strain relaxation.Thus,the crystal quality is the mian fator affecting the EQE for green and yellow LEDs,while the increased holes concentration should play a leading role for blue LEDs.4?By investigating the effects of conventional quantum wells with the same growth temperature and the combined quantum well structure with confined well(close to n-GaN)and lighting well(close to p-GaN)on green LEDs respectively,it was found that the lighting wells close to p-GaN have a strong storage and confinement effect,which not only increased the carrier concentration in lighting wells,enhancing the overlap of electron and hole wavelength function and thus improving the EQE,but also reduced the IQE collapse at the low temperatures.