Wavelength selective detection using excitonic resonances in multiquantum-well structures

The wavelength and voltage dependence of photocurrent near excitonic resonances are used to study the wavelength selectivity of p-i(multiple quantum well, or MQW)-n photodiode structures with a parallel sequence of optical bits, each with a different wavelength. The selectivity is considered good if the state of a λ_i wavelength bit can be detected regardless of λ_j(j ≠i) state of the bits. Photocurrent is found to have very good selectivity only if λ_j bits are all zero, i.e., the optical information is serial, but it is also found that differential photocurrent (ΔI_ph/ΔV ) provides a good selectivity for random states of λ_j bits (i.e., parallel input). Four channel selectivity is demonstrated at 200 K. Specifically designed quantum-well structures can greatly improve this selectivity