Long-wavelength λc=18 μm infrared hot-electron transistor

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Abstract
A long‐wavelength λc=18 μm infrared hot‐electron transistor (IHET) with low dark current is demonstrated. In order to achieve long‐wavelength absorption, a low barrier height is required, which in turn results in a large dark current. Therefore, operation of a normal long‐wavelength quantum‐well infrared photodetector (QWIP) structure is limited to very low temperatures and biases due to the thermally activated dark current. In the IHET, a high‐energy pass filter placed after 30 periods of GaAs/AlGaAs quantum wells blocks the temperature‐activated dark current while allowing high‐energy photoexcited electrons to pass and be collected as photocurrent. A comparison of the dark current to the 300 K background photocurrent shows that the QWIP structure without the high‐energy pass filter demonstrates background‐limited infrared photodetection (BLIP) only at T≤35 K. Furthermore, in order to avoid saturating a typical readout circuit, detector operation of the QWIP is restricted to biases less than 0.08 V at 35 K. In contrast, the filtered dark current in the IHET is reduced by two to four orders of magnitude such that BLIP performance can be achieved for temperatures up to T=55 K without saturating the readout circuit. Because of the preferential current filtering effect, the noise equivalent temperature difference of the IHET can be improved by a factor of 100 at T=55 K. The dark‐current‐limited detectivity was found to be D*=1×1010 cm Hz1/2/W at λp=15 μm, Ve=−0.2 V, and T=55 K.