Efficient light emitting diodes by photon recycling and their application in pixelless infrared imaging devices

The success of the pixelless imaging concept using a quantum well infrared photodetector integrated with a light emitting diode (QWIP-LED) depends cri tically on the extent of spatial lateral spreading of both photocurrent gen erated in the QWIP and near infrared (NIR) photons emitted by the LED as th ey escape from the device layers. According to the photon recycling model p roposed by Schnitzer [Appl. Phys. Lett. 62, 131 (1993)] there appears to be a trade-off between a high LED external quantum efficiency and a small pho ton lateral spread, the former being a necessary condition for achieving hi gh detector sensitivity. This lateral spreading due to multireflections and reincarnations of the NIR photons could potentially degrade the image qual ity or resolution of the device. By adapting Schnitzer's model to the QWIP- LED structure, we have identified device parameters that could potentially influence the NIR photon lateral spread and the LED external efficiency. In addition, we have developed a simple sequential model to estimate the cros stalk between the incoming far infrared image and the up-converted NIR imag e. We have found that the thickness of the LED is an important parameter th at needs to be optimized in order to maximize the external efficiency and t o minimize the crosstalk. A 6000-Angstrom-thick LED active layer should giv e a resolution of similar to 30 mu m and an external efficiency of similar to 10%. (C) 2000 American Institute of Physics. [S0021-8979(00)08603-5].