Effect Of Medium-high Temperature Interlayer On The Optical And Electrical Properties Of GaN Based Blue Light Emitting Diodes

GaN-based blue light-emitting diodes(LEDs) have been widely used in general lighting, displaying and other areas because of their high luminous efficiency, small size and so on. The typical dislocation density of InGaN/GaN MQW LEDs has a range of 108-1010/cm-2, whereas the electroluminescence efficiency can up to 40%-60% and this phenomenon has been attracted considerable interest for researchers. In this work, the optical and electrical properties of LED chips were discussed based on the self-screening effect of V-shaped pits, which influenced by the size of V-pits; on the other hand the optical and electrical properties of LED chips were analyzed, which influenced by temperature gradient layers.GaN-based blue light emitting diodes(LEDs) were grown on patterned sapphire substrates by metal-organic chemical vapor deposition(MOCVD) method. 1)the size of V-pits were controlled by different thicknesses of medium-high temperature. The optical and electrical properties of LEDs influenced by the size of V-pits had been investigated, and the relevant physical mechanism was discussed; 2)the optical and electrical properties of LEDs influenced by temperature gradient layers had been studied, and its relevant physical mechanism was discussed. The detail consequences as follows:1)Crystal quality, optical and electrical properties, surface morphology have been characterized by high-resolution X-ray diffraction(HRXRD), photoluminescence spectroscopy(PL), LED test system and atomic force microscopy(AFM), respectively. As the thickness of medium-high temperature interlayer was increased from 60 nm to 100 nm, the size of V-pits were enlarged from 70-110 nm to 110-150 nm. For the optical results, with the excitation power increasing, the redshift of peak wavelength were 1.8 nm and 1 nm, then all samples showed a blueshift of 2 nm. For the electrical results, the chip light output power was improved from 21.9 mW to 24.1 mW at injection current of 20 mA. As injection current increasing from 1 mA to 40 mA, the buleshift of peak wavelength were 6.5 nm, 4.2 nm and the FWHM broadened 5.9 nm and 7.5 nm respectively. As the size of V-pits increased, it was beneficial to enhance the holes injection area and injection depth, thus the light output power of the LED device was improved.2)Crystal quality, optical and electrical properties have been characterized by high-resolution X-ray Diffraction(HRXRD), photoluminescence spectroscopy(PL) and LED test system, respectively. For the sample grown with temperature gradient layer, the FWHM of XRD rocking curve for(002) and(102) plane were decreased from 290 to 251 arsec, 281 to 242 arsec, respectively. PL integrated intensity was improved by 13.9%. At 20 mA injection current, the light output power of chips were improved from 31.2-32.0 mW to 33.7-34.5 mW, and the forward voltage of chips were nearly decreased 0.1 V. All results show that the optical and electrical properties were improved with the temperature gradient layer which plays an important role of reducing the dislocation density and strain relaxation in InGaN/GaN MQWs.