A four-color quantum well infrared photodetector

A four-color quantum well infrared photodetector (QWIP) has been demonstrat ed in this work. Four stacks of quantum well structures with four different detection wavelengths are sandwiched among three highly doped contact laye rs. The peak wavelengths of the four colors are centered at 4.7, 8.5, 9, an d 12.3 mu m. The 4.7 and 8.5 mu m stacks are separated from the 9 and 12.3 mu m stacks by a middle ohmic contact layer, and the change of peak detecti on wavelengths within the two-stack QWIPs is achieved by varying the bias v oltage. Four different combinations of two-color simultaneous reading can b e obtained. The detector could achieve simultaneous reading of four colors by adding two extra contact layers to the design with appropriate readout c ircuitry. By using a small number of quantum wells, we are able to use all four stacks for voltage-tunable detection with two terminals. In spite of u sing InGaAs/AlGaAs and GaAs/AlGaAs materials in the four stacks, the device shows excellent material quality and performance characteristics. (C) 1999 American Institute of Physics. [S0003-6951(99)04909-8].