Study On The Effect Of The Growth Process Of Active Region On Photoelectric Properties Of GaN-based Green LED On Si Substrates

GaN-based LEDs have been widely used in the solid state lighting field because their light emission wavelength can be continuously adjusted from infrared to ultraviolet.However,the development of the luminous efficiency of LEDs with different wavelength is extremely unbalanced.Currently,GaN-based blue LEDs have reached commercial standards,while the luminous efficiency of LEDs in the yellow-green light band is still at a low level due to high indium composition and large stress,which is called "yellow-green gap" phenomenon.This has become an important bottleneck restricting the development of multi-primary colors mixed white LEDs lighting.Thus,it is necessary to further study how to improve the luminous efficiency of yellow and green LEDs.In this paper,by changing the growth condition and structure in the active region,the effect on the photoelectric properties of the GaN based green LEDs on Si substrate is investigated in order to further improve the luminous performance.The following research results are mainly obtained.1.The effect of quantum barriers(QBs)growth rate on the quantum wells(QWs)crystal quality and the photoelectric properties of GaN-based green LEDs were studied by regulating the TEGa flow rate during the growth process of QBs.When the QBs growth rate was reduced,the N vacancies formed in the quantum well are reduced,and the large-sized In-rich clusters are effectively alleviated,thereby the crystal quality of the quantum well is significantly improved.At the same time,with the decreasing of QBs growth rate,QW/QB interface becomes more abrupt and the carrier confinement ability improved.This makes the samples with the lower QBs growth rate show higher external quantum efficiency in the entire test current density range(0.001-75 A/cm2).In addition,after the growth rate of the QBs is reduced,the reverse leakage current of the LEDs is alleviated.It is further verified that the lower QBs growth rate is beneficial to the improvement of QWs crystal quality.2.Based on the traditional InGaN/GaN superlattice preparation layer,the preparation layer is divided into three sections for growth,and the GaN barrier at the seperation is heavily doped with Si.The effects of Si doped in the preparation layer on the photoelectric performance of GaN-based green LEDs were investigated.The results show that after the preparation layer was doped with Si,the forward voltage of the LEDs was reduced,and the wall-plug efficiency(WPE)was improved at the operating current density of 35 A/cm2.The improved performance is closely related to the height of the heterojunction potential barrier in the preparation layer region,and the doping of Si can reduce the potential barrier to a certain extent.However,after the preparation layer is doped with silicon,the crystal quality of the QWs active region deteriorates,resulting in an increase in the forward and reverse leakage current of the LEDs.This is because the preparation layer is divided into three sections to grow and silicon doping will introduce more defects,which will damage the quality of the QWs.In addition,under the low-temperature,electroluminescence(EL)spectrum can be observed that the sample doped with Si in the preparation layer has a stronger electron leakage peak,indicating that its electron overflow is more serious.We attribute this phenomenon to the lower potential barrier of the preparation layer region,which makes it easier for electrons to be injected into the QWs,and the electron and hole concentrations at low temperatures are seriously mismatched,making it easier for electrons to flow from the QWs to the p-type layer.3.The effect of preparation layer thickness on the photoelectric performance of GaN-based green LEDs on Si substrates was studied.The results show that as the thickness of the preparation layer increases,large-sized indium-rich clusters generated in the QWs are gradually eliminated,and the forward leakage current of the LEDs is alleviated.However,samples with thicker preparation layers have more severe reverse leakage due to the increase in the size and density of the V-shaped pits.It is precisely due to the size of the V-shaped pit is increased and the hole injection efficiency is improved,which effectively reduces the forward voltage of the LEDs,thereby improving the luminous efficiency of the LEDs.Besides,because the preparation layer has the effect of releasing the stress in the QWs,the sample with a thicker preparation layer has a smaller blue shift of the EL spectrum peak wavelength in a low current density range.