A quantum well infrared focal plane array achieves hyper-spectral measurements of incident infrared radiation using a voltage dividing network that applies different and adjustable biasing voltages to each line of the line by column array. The peak wavelengths of each quantum well layer of each detector structure in the array is set to a specified nominal value by appropriate fabrication of the depths of the quantum wells of the layers. The nominal peak wavelength value of each quantum well layer can further be varied by modulating the bias voltage applied to the gate of the direct injection transistor associated with each detector structure of the array. A read out integrated circuit (ROIC) containing the direct injection transistor processes the photo-current from each quantum well layer of each detector structure. Using an n by n array of vertically stacked detector structures, along with the associated ROIC, a focal plane array can be fabricated where each row of detector elements in the array is responsive to different peak wavelengths.