Study On Material Growth Unit Technology Of GaN Based Near Ultraviolet And Yellow LED On Silicon Substrate

Nowadays,the research on the III-nitride based LED has made a breakthrough,the internal quantum efficiency of blue LED has achieved to 85% 87%.In order to meet the application requirements of different band,the research focus of GaN based LED turns to high Al-and In-composition.In this thesis,the material growth unit technology,which affects the properties of LED,has been studied by using the GaN based near ultraviolet LED on Si substrate and GaN based yellow LED on Si substrate as the carriers with larger material mismatch and stronger polarization of electric field.In GaN based near ultraviolet LED on Si substrate section,mainly studied AlGaN quantum barrier growth unit technology and V-pit growth unit technology.In GaN based yellow LED on Si substrate section,mainly studied p-AlGaN EBL growth unit technology.The main achievements are as follows:1?The AlGaN quantum barrier structure with different Al composition was designed and grown.The physical mechanism of Al composition affecting the property of GaN based near ultraviolet LED on Si substrate was discussed,and the optimized Al composition was determined.The experiments results show that Al composition in AlGaN quantum barrier affects carrier confinement of active region and results in band-bending effect of EBL,which in turn exerts dramatically effect on quantum efficiency and efficiency droop of LED.Thus the Al composition should not be too high or be too small.The optimized Al composition in AlGaN quantum barrier of GaN based near ultraviolet LED on Si substrate?395 nm?is 15%.2?The V-pit size changes by manipulating the thickness of LT-GaN interlayer.It is found that there are two sets of V-pit with different sizes on the surface of QWs.Innovatively proposed the influence of each set of V-pit on the LED property is different and studied separately.The optimized V-pit size of GaN based near ultraviolet LED on Si substrate was determined,and the effect of the V-pit in the LED was supplemented and expanded.The experiments results show that V-pit could screen dislocation,suppress nonradiative recombination and enhance hole injection if its size in reasonable range.The optoelectronic properties of LED improve with the increase of V-pit size.However,if V-pit size beyond reasonable size,the quantum well effective emission area may decrease as well as the epitaxial properties,which result in device properties deteriorate with the increase of V-pit size.The optimized V-pit size is approximately 120-190 nm.Whether the V-pit size is too large or too small will deteriorate the properties of devices seriously.The related research results have been accepted by Journal of Luminescence.3?The p-AlGaN EBL growth unit technology was studied by manipulating the p-AlGaN EBL growth NH₃ flow rate.The dependence between p-AlGaN EBL growth NH₃ flow rate and unintentional C and O contaminations concentrations was investigated.The physical mechanism of the influence of C and O contaminations on the GaN based yellow LED on Si substrate was investigated.A new hole injection mechanism combining with schematic structure of V-pit was employed to account for these experiment results.Temperature and injection current dependent EQE and EL spectra were employed to verify the variation of hole concentration and hole injection mechanism.Considering the optical and electronic parameters as well as growth technology comprehensively,we found out the most appropriate value of p-AlGaN EBL growth NH₃ flow rate in our case.It is found that the concentrations of C and O contaminations increase as p-AlGaN EBL growth NH₃ flow rate decrease,which may be contributed to the formation of deep donor complex?CN-ON?due to its relatively low formation energy.The deep donor complex?CN-ON?is an effective compensation center for MgGa,leading to low effective hole concentration and high electrical resistivity of p-AlGaN EBL in flat region and sidewall of V-pit.The relative magnitude of electrical resistivity of p-AlGaN EBL in flat region and sidewall of V-pit decides the hole injection mechanism.The variation in hole injection mechanism causes distinct difference in optical and electronic characteristic of LEDs.When holes are mainly injected through flat region,temperature and injection current dependent EQE achieve maximum only in 100 K,EL spectra can only be observed the main emission peak and longitudinal optical phonon replicas.When holes are mainly injected through V-pit,EL spectra can be observed Mg-related emission peak,superlattice emission peak and sidewall quantum wells emission peak.p-AlGaN EBL growth NH₃ flow rate could not be too high due to serious prereactions,and could not too low due to high concentrations of C and O contaminations.Considering the optical and electronic parameters as well as growth technology comprehensively,we conclude that 1500 sccm is the most appropriate value of p-AlGaN EBL growth NH₃ flow rate in our case and excellent optoelectronic properties of InGaN/GaN yellow LEDs are obtained.The EQE,Vf,WPE and FWHM is 22.0%,2.363 V,20.42% and 39.4 nm,at a certain current density of 20 A/cm2,respectively.