Research Of Passivation Layers And P-GaN Ohmic Contacts On GaN Based LED On Si Substrates

The epitaxial growth of GaN on Si substrate has made much progress in recent years. The reliability and the improvement of the efficiency are primary concerns for optoelectronic devices. Compare to the lateral LEDs, the vertical structure LEDs based on Si substrate have no current crowding and thermal conductivity problems. Besides, the use of the metal reflector and surface roughening can enhance the light extraction efficiency. In addition, it is easier and cheaper to remove the Si substrate by simple chemical etching than sapphire substrate. Therefore, the VCLED on Si substrate is a promising way to gain good reliability. However, it is in infancy, there is still a long way for GaN LED based on Si substrate.In this thesis, we have studied the effects of SiON passivation layer on reliability of GaN based blue and green LEDs on silicon substrate and the ohmic contact of Ni/Ag/Cr/Pt to P-GaN under different annealing temperature and different activated conditions of Mg. Some significant and innovative results are achieved as follows.Accelerate four-type LEDs (Sample A was uncoated. top-surface of sample B, sidewall of sample C and both top-surface and sidewall of sample D was coated with SiON passivation layer) under great current density of 312 A/cm2. The results show that the SiON passivation layer (especially the sidewall-SiON) could decrease the generation of non-recombination centers, decrease leakage currents, luminous decay and so on. The enhancement of the LOP of Si-based LED coated with SiON are 12.9% and 7.4% for blue and green LED, respectively. By the way, the lumious decay of the samples without SiON layers is just 10.95% tested at 20mA even after aging at great current density of 312 A/cm2. After aging at high current density of 156A/cm2 for 1032 hours. The dominant wavelength shifts and increases of VF2 for green LEDs are just 0.7nm and 0.003nm, which is attributed to the excellent reliability of LEDs with Si Substrate. The SiON could absorb short wavelength radiation and separate the epoxy from hot surface of LED chip, which helped preventing the epoxy from carbonization.It is for the first time that we use sapphire to simulating the interface of Ag and P-GaN under different annealing temperature and different Mg activated conditions. The reflectivity of Ag was tested under these conditions based on this method. The results show that the formation of NiO could enhance some reflectivity. The reflectivity of Ag with Pt activated, annealing at 400℃is the best but decrease when temperature further increase. The I-V characteristic of Ni/Ag/Cr/Pt contacts to p-GaN with Si Substrate annealing in different temperature, with different activated conditions of Mg was investigated. The results show that the one actived with Pt, annealing at 300℃, exhibit the best electrical properties, but then decrease, and there are little difference between the one with Ni-actived. Considering the influence of I-V and refelctivity, We refer that the one annealing at 500℃, actived with Ni is the best one。By comparing the reflectivity with and without Cr/Pt capping layer and the roughness of AFM testing, under different annealing temperature, the results show that the decrease of reflectivity is attributed to Ag agglomeration. The Cr/Pt capping layer could enhance the reflectivity, which is due to Cr/Pt could protect Ag from agglomeration. The reflectivity is 92.68% test on the glass at 400℃, which is close to the theoretical data 96%.Part of the research results have been used in the chip manufacture. This work was supported by the National 863 Program and ministry of education of china Semiconductor Luminance Innovative Research Team in University.