Photocurrent Measurement of Quantum Well Device

We can obtain information about the device structure using photocurrent measurements. As the word photocurrent suggest the measurement involves the use of light to excite electrons for valence band to conduction band by absorption of photons by the electrons. As absorption in semiconductor is determined by the density of photons, density of electrons in valence band and density of empty states in conduction band. if the incident photon has energy larger than bandgap, electron absorbing it will be excited to the conduction band and this is current generation and can be detected using very sensitive equipment such as lock-in amplifier in my case SR830. if we run negative bias across the device the amount of photons with lower energies absorbed increases. Therefore we can determine the bandedge and hence use this feature in Modulators. It is interesting to observe an absorption peak just below the bandedge due to the presence of excitons. The presence of excitons is important feature for Modulators exploiting Quantum Confined Stark Effect.