Electroluminescence properties of vertical structure GaN based LED on silicon and copper submount at different temperatures and current densities

Abstract

GaN-based light-emitting diode (LED) thin films grown on Si(111) substrates are successfully detached and transferred to copper and silicon submounts, and then become 40mil high power vertical structure LED chips. Electroluminescence properties of the two kinds of chips with the same expitaxial structure are investigated at different forward current densities and ambient temperatures. The obtained results are as follows. 1) at the same temperature, the EL peak wavelength of the chip with copper submount is longer than that of the chip with silicon submount. Under 13 K, the EL peak wavelength of the chip with copper submount is about 6 nm longer than that of chip with silicon submount as the driving current increases from 0.01 mA to 400 mA. While under 300 K, the difference in EL peak wavelength between the two kinds of chips at 0.01 mA is only about 3 nm; as the current increases to 400 mA, the difference will tend to zero and the spectra will coincide. 2) At the same current density, as the temperature increases from 13 K to 320 K, the EL peak wavelengths of the two kinds of chips are S-shaped, and the spectra tend to coincide. 3)When the temperature is below 100 K, the current density droop effect of the chips with copper submount is more abvious than that of chips with silicon submount, while above 100 K, the results are just inverse. Perhaps, it is due to the fact that the differences in thermal expansion coefficient and thermal conductivity between the two kinds of submounts lead to the diffrent EL properties.