A light-absorbing device and method employ a series of photon-absorbing semiconductor substructures. A first semiconductor substructure provides first and second energy states. A difference between the first and second states being such as to cause an electron to be promoted from the first state to the second state upon absorption of a photon of a first energy. A second semiconductor substructure provides third and fourth energy states. The third state is arranged to receive the electron from the second state. A difference between the third and fourth states being such as to cause the electron to be promoted from the third state to the fourth state upon absorption of a subsequent photon of a second energy. The third state has a lower energy than the second state, such as to cause the electron to dissipate energy as it passes from the second state to the third state.