1. A spectrally tunable detector comprising: a first barrier region disposed on a first conductive region; an absorbing region that is based at least in part on intersubband transitions of quantum states, wherein the absorbing region comprises: a first quantum well region disposed on the first barrier region, a quantum dot region disposed on the first quantum well region, and a second quantum well region disposed on the quantum dot region, wherein the second quantum well region has a different material composition than the first quantum well region, and wherein the different material composition cause a vertical asymmetry in a local potential seen by carriers, a second barrier region positioned on the second quantum well region, wherein the first barrier region and the second barrier region contribute to the vertical in the local potential; and a second conductive region disposed on the second barrier region, wherein both the first conductive region and the second conductive region comprise a highly doped semiconductor material having a same conductivity type.