Abstract: An infrared detector has a multi-layer structure to simultaneously detect IR energy in different spectral bands without changing polarity of a bias imposed across the detector. Two absorption layers are separated by a barrier layer that imposes an electrical potential barrier to one of the absorption layers. Under low bias in one direction, only one layer generates a photocurrent. Under a higher bias in the same direction, both layers generate a photocurrent. Additional absorption layers may be added to detect additional bands of energy, where the additional absorption layers generate photocurrent under a bias in another direction. Two, three, and four band detection is disclosed. Where absorbing layers within a single unit cell absorb under different bias direction, the barrier layer between those different bias direction layers suppresses a diffusing electron current. A method for detecting and resolving energy absorbed in two, three, and four different energy bands is also provided.