LONG-WAVELENGTH LAMBDA(C)=18-MU-M INFRARED HOT-ELECTRON TRANSISTOR

A long-wavelength lambda(c) = 18 mum 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 tum results in a large dark current. Therefore, operation of a normal lon g-wavelength quantum-well infrared photodetector (QWIP) structure is l imited to very low temperatures and biases due to the thermally activa ted dark current. In the IHET, a high-energy pass filter placed after 30 periods of GaAs/AlGaAs quantum wells blocks the temperature-activat ed dark current while allowing high-energy photoexcited electrons to p ass and be collected as photocurrent. A comparison of the dark current to the 300 K background photocurrent shows that the QWIP structure wi thout the high-energy pass filter demonstrates background-limited infr ared photodetection (BLIP) only at T less-than-or-equal-to 35 K. Furth ermore, in order to avoid saturating a typical readout circuit, detect or operation of the QWIP is restricted to biases less than 0.08 V at 3 5 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 achi eved for temperatures up to T = 55 K without saturating the readout ci rcuit. Because of the preferential current filtering effect, the noise equivalent temperature difference of the IHET can be improved by a fa ctor of 100 at T = 55 K. The dark-current-limited detectivity was foun d to be D = 1 X 10(10) cm Hz1/2/W at lambda(p) = 15 mum, V(e) = -0.2 V, and T = 55 K.