Detailed investigation of electron transport, capture and gain in Al_0.3Ga_0.7As/GaAs quantum well infrared photodetectors

Abstract

We present an investigation of Al 0.3 Ga 0.7 As/GaAs quantum well infrared photodetectors (QWIPs) through detailed ensemble Monte Carlo simulations. Both two-dimensional and three-dimensional electrons are simulated with realistically evaluated scattering rates. Transport of the excited electrons is accurately modelled including the reflections from well-barrier interfaces. The details incorporated into the simulator clarified some important phenomena, as well as verifying the previous predictions. Under large bias, well accumulation occurs non-uniformly, being highest near the emitter. Contrary to previous assumptions, the L valley is found to be the origin of a significant portion of the captured electrons even under typical bias voltages. -L transfer, while decreasing carrier mobility, also increases capture probability and decreases the electron lifetime, having a twofold effect on device gain. The above findings explain the large difference between the gains of Al x Ga 1−x As/GaAs (with x ∼ 0.3) and InP/In 0.53 Ga 0.47 As (or GaAs/In x Ga 1−x As) QWIPs, as well as the bias dependence of gain. The average barrier electron velocity is close to the saturated electron velocity in bulk Al 0.3 Ga 0.7 As under moderate and large bias; however, low-field mobility is significantly lower than that in bulk material. While complementing previous work, our results offer a deeper understanding of some important QWIP characteristics by resolving the details of transport and electron dynamics in the device.

A microscopic model of quantum well infrared photodetectors (QWIP)

“…Moreover, megapixel, highly uniform QWIP focal plane arrays have been reported with a wide range of possible applications [9,10]. However, despite the extensive amount of experimental and theoretical efforts, not much work has been done on microscopical quantum description of the processes that govern both vertical and parallel electron transport in periodic quantum structures, involving bound-bound and bound-continuum intersubband transitions [6,[11][12][13]. In order to ensure further improvement of the QWIP technology, primarily by using novel structures and material systems, a thorough understanding of fundamental physical processes in QWIPs, as well as first principles simulation tool are necessary.…”

Optically addressed near and long-wave infrared multiband photodetectors

“…LWIR responsivity has a negative differential slope on À1 to À2 V electrical bias range, consistent with early reports and related with intervalley transfer of electrons. 24,27,28 The result shows that the p-i-n sub-photodetector does not affect the transport characteristics of the QWIP under the reported operating conditions, and the LWIR QWIP signal is as high as its single band counterparts. 24 In NIR mode, photodetector noise is limited by the system noise which is above the shot noise limit due to low current density, on the order of 10 À6 A/cm 2 at 68 K. In summary, NIR/LWIR optically addressed dual band infrared photodetector has been experimentally demonstrated.…”

Characteristics of high responsivity 8.5μm InGaAs/InP QWIPs grown by metalorganic vapour phase epitaxy

“…Of all these, QWIPs based on GaAs/AlGaAs materials are the most advanced for infrared imaging applications because of the mature material synthesis and processing technology of these materials. In recent times, there has been a renewed interest in QWIPs based on InGaAs/InP materials [4][5][6][7][8][9][10][11][12][13][14][15]. A significant advance is the reports of focal plane array imaging camera based on this material system [16,17].…”