Study Of Growth Conditions On Photoelectric Properties Of GaN Based Yellow Light LED On Silicon Substrate

Due to the excellent electrochemical properties,Ga N-Based materials has been widely used in microelectronic and optoelectronic.Moreover,with the rapid development of semiconductor technology and process,it has been successfully prepared form high power blue,green and ultraviolet LED devices.In particularly,the blue LED has made outstanding achievements,of which internal quantum efficiency is up to 85~87%.At present,white-light illumination usually based on blue light with phosphor coversion.Even though this way has the advantage of high efficiency,it still has amounts of problems that blue light occupies a relatively high proportion,and color rendering index and efficiency are difficult to take account of simultaneously.In order to further improve the lighting quality,it is necessary to improve the efficiency of long band LED,especially the yellow light.In this paper,the structural characteristics of the materials and the photoelectric properties of the devices under different growth conditions are studied on the basis of the work of the previous researchers,By optimizing the growth pressure of the Yellow LED quantum well,the growth rate of the P-AlGaN electron barrier layer,the Si doping concentration of the quantum barrier layer and the electron injection layer before the well,The following research results are mainly obtained.1.The growth pressure of quantum wells of Ga N-based yellow LED was regulated,different growth pressure of quantum well structure characteristics and the influence of the photoelectric performance were studied,which lead the optimum growth pressure of GaN based yellow LED quantum well was determined.The experimental results show that increasing the growth pressure of quantum wells could reduced the In fraction slightly but raised the homogeneity.It shows that the sample have fewer In clusters,N vacancies and better crystal quality,which provide positive effect on photoelectric performance.However,with the increasing of growth pressure,interface between well and barrier becomes ambiguous.It's accredited to the weakened carrier confinement.Thus,the current droop effect is intensified.The EQE of the device is mainly affected by the defects number and the interface quality between well and barrier.The sample grown at 75torr has obtained the optimal performance in the working current at 20 A/cm~2.2.The effect of growth rate on the P-AlGaN EBL crystal quality and the photoelectric properties of GaN-based yellow light LED was studied by regulating the growth rate of P-AlGaN EBL.With the decreasing of growth rate,C atoms have more time to desorb from surface.When the growth rate was improved,C atoms adsorbed on the surface of the epitaxial film can be buried in the epitaxial layer by the newly deposited atoms,which leads to the increase C concentration.Moreover,the memory effect of In is more obvious under the higher growth rate.The crystal quality of P-AlGaN was deteriorated because of the presence of these impurity atoms which will further affect the photoelectric properties of the materials.Futher more,the thickness of the platform quantum well is larger than that of the sidewall of V-pits,the holes need to overcome higher energy barrier through the c-plane MQWs at low temperature.The holes are insufficient while it is degraded for crystal quality of P-AlGaN,which was contributed to the reduced activation efficiency of Mg.Therefore,the holes are tending to inject sidewall of V-pits,the emitting peak of sidewall quantum is more obvious because of higher injected proportion of holes.3.The influence of different Si doping positions and concentration on the photoelectric performance of GaN-based yellow LED was studied by using Si doping in first four barrier and the electron injection layer respectively.In the designed concentration range of Si,as the Si concentration in the first four barrier increasing,the interface between well and barrier becomes steeper.At the same time,both forward voltage and reverse leakage are improved.It is mainly due to the doped Si in the yellow LED deteriorated the crystal quality of device,which promote the trap-assisted tunneling.It was observed that increasing the Si concentration of barrier,the holes localization effect was enhanced in the MQWs near P-types,resulting in increasing EQE under small current density and decreasing EQE under small current density.Meanwhile,Si doped in the electron injection layer before MQWs can seriously damage the crystal quality of the GaN epitaxial film.It is reflected in the large forward voltage and reverse leakage.the fluorescence also shows an ununiform image.There is almost no light emitting under small current density,and the overall EQE is lower than other samples.