International Radiation Detectors, Inc.

Temperature Dependence

Figure 1 shows the temperature dependence of the AXUV, SXUV and UVG diodes responsivity at 254 nm. Typically the responsivity was found to increase by .03% per degree Celsius. As shown in Figure 2, the temperature dependence of AXUV and SXUV diode responsivity is essentially the same down to 1 nm. This suggests that the responsivity temperature dependence in this region is caused by an increase in the quantum yield (owing to reduction in the bandgap) with higher temperature.

Because of presence of surface recombination in the SXUV diodes, their responsivity temperature dependence is expected to be lower then that of the AXUV diodes. The surface recombination is known to have negative temperature dependence. However, we have not been able to verify the lower temperature dependence of the SXUV responsivity experimentally.

Fig. 1: Change in 254 nm responsivity of AXUV, SXUV and UVG photodiodes with temperature

Fig. 2: Change in the SXUV and AXUV photodiode responsivity with temperature

The positive temperature coefficient of responsivity at wavelengths above 700 nm shown in Figure 2 above is caused by an increase in the minority carrier lifetime with temperature. The increased lifetime results into increased diffusion length and thus higher carrier collection.

Fig. 3 shows typical temperature dependence of the shunt resistance of AXUV/UVG/SXUV photodiodes. The shunt resistance was found to decrease by a factor of 2 for every 7.5°C rise in temperature.

Fig. 3: Change in shunt resistance of AXUV, SXUV and UVG photodiodes with temperature.

Fig. 4 shows the typical temperature dependence of capacitance for the IRD photodiodes over a temperature range of 0°C to 40°C. The positive temperature dependence of diode capacitance occurs because the intrinsic carrier concentration increases with temperature which results in the reduction of built-in potential.

Fig. 4: Temperature dependence of zero bias capacitance of AXUV, SXUV and UVG diodes, with 5 mm dia. active area.