Effects of graded barriers on the operation of split-off band infrared detectors

Increasing the operating temperature of infrared detectors is a prime importance for practical applications. The use of split-off band transitions has been proposed for high operating temperature infrared detectors. Initial results showed increasing the potential barrier for free carrier emission has led to increases in operating temperature from 150 K for a detector with an 8 μm threshold to room temperature for detector with a 4 μm threshold. However, these detectors showed a low responsivity due to the capture of carriers in each emitter. A proposal was made to use graded barriers with an offset between the barriers on the two sides of an emitter as a method of reducing the capture in the emitters. Two GaAs/AlGaAs samples with a single graded barrier (Al fraction x = 0.57 to 1 and 0.45 to 0.75, respectively) were used to test the effects. The sample with the lower barrier show responsivity increased by a factor of ∼10 or more compared to the higher graded barrier sample and detectors without the graded barrier. The higher graded barrier sample, space charge build up causes almost all potential drop across the first barrier, and hence reduces the response. Based on the modeling it is believed that this effect will be greatly reduced in detectors with multiple periods of graded barriers and emitters, allowing the full gain effects of the graded barriers to be realized.