High energy radiation effects on LED's

The 8 MeV electron irradiation on GaN based LED chips creates significant changes in the I-V characteristics (upto 6.8x1014 e/cm2 ) only at the lower bias region. However, emission spectra reveal that there are some defects that are present in the pre-irradiated samples as well as in post irradiated samples. These defects correspond to those identified for n-GaN grown by MOCVD process. Three of these traps correspond to 1 MeV electron radiation induced traps previously reported in GaN. In addition, electron irradiation has introduced two more defects.The effect of high-energy Li ions (40 MeV) on the Green LED chips show a decrease in the operating voltage. The degradation was observed in the chip at the lowest fluence.For high (5x1012 ions/ cm2) fluence the I-V curve does not exhibit the turn-on voltage region. The degradation mechanism appears to be from creation of recombination centers and traps. This is confirmed by DLTS studies on green LED chips.From the emission spectra it can be seen that the wavelength increases as the fluence is increased. This suggests that irradiation has induced defects in, at least, the junction region, thereby degrading LED efficiency.