Influence of temperature on different optoelectronic characteristics of InGaN light emitting diodes

We have measured the electroluminescence (EL) and carrier lifetime characteristics in InGaN/Sapphire purple light emitting diode (LED), namely, UV3TZ-405-30 in a temperature range from 350 to 120 K and have compared them with those of a similar LED (UV3TZ-395-15) but with different Indium concentration, measured earlier. While it is found that for the present device the EL intensity decreases drastically with lowering of temperature after reaching a maximum (99%) at 228 K, this is markedly different from the previous device where intensity continues to increase monotonically till lowest temperature. This qualitatively distinct temperature dependence indicates difference in nature of localisation of carriers in the multiple quantum wells for varying Indium content in the two devices. The light–current–temperature data have been analysed in terms of the semiconductor rate equations to determine different optoelectronic properties. Next, estimating the ideality factor from the current–voltage (I–V) measurements, the effective carrier lifetime has been evaluated from the open circuit voltage decay process. Using the above measurements, the temperature dependence of the internal quantum efficiency of the device has been calculated and it is found to attain a maximum value of 99.88% at 228 K. Unlike all previous calculations, a unique feature of the present approach has been to include the effect of temperature dependence of the radiative recombination coefficient (B) in the rate equation analysis. Finally, a comparative study of the temperature dependence of the different optoelectronic properties of both devices is presented with and without this effect.