The development of some applications on silicon(Si) substrates has obvious technological advan-(tages)

including the low cost

large-scale availability

good thermal and electrical conductivities and the feasibility of removing the Si substrates with wet etching.Significant mismatches in lattice constants and thermal expansion coefficients of silicon and GaN in growth process is encounted

such differences cause crack formation when the thickness of the grown film exceeds a critical thickness.Recently

considerable developments in this field has been achieved

GaN LED grown successfully on Si was reported.Junction temperature is a key parameter of light emitting diode(LED)

the junction temperature characteristic of GaN LED on Si substrate is reported firstly.The junction temperature of GaN on Si was measured under forward voltage.This method is based on the dependence of junction temperature on operating voltage.This relationship can be measured and used to compute the semiconductor junction temperatures in response to power dissipation in the junction region.This measurement consists of two steps of measuring: the calibration measurement and the actual junction-temperature measurement.The results showed that the junction temperature of GaN LEDs on Si substrate is different from that on sapphire substrates.The junction temperature on Si substrate is lower than that on sapphire

and the increase speed of the junction temperature is lower on Si substrate than that on sapphire substrate

especially in high operating current.We believe that this phenomena results from the better thermal conductivity of Si substrate than sapphire substrate(the thermal conductivity for Si and sapphire are 5 W/cm·K and 1.5 W/cm·K

respectively).The result that junction temperature is still low in high current suggests that the GaN-base LEDs on Si substrate have much more potential for the application on the high power devices.