Multicolor voltage tunable quantum well infrared photodetector

Using intersubband transitions in quantum wells to produce long wavelength infrared (IR) devices is well known. The most successful example to-day is the quantum well infrared photodetector (QWIP). We present a novel concept of a multicolor QWIP by stacking the usual one-color QWIPs separated by thin (z 100 nm in our test structure) conducting layers. We rely on the highly non-linear and exponential nature of the device dark current-voltage characteristics. This implies that an applied voltage across the entire multistack would be distributed among the one-color QWIPs according to their values of dc resistances. Thus, when the applied voltage is increased from zero, most of the voltage will be dropped across the one-color QWIP with the highest resistance. As the voltage is further increased, an increasing fraction of the voltage will be dropped across the next highest resistance onecolor QWIP, and so on. Since the detector responsivity of a one-color QWIP gradually turns on with applied voltage, we therefore can achieve a multicolor QWIP with spectral response peaks that turn on sequentially with an applied voltage. The bandedge profiles of a three-color version under different bias conditions are schematically shown in Fig. 1.