Electric-field effects in semiconductor quantum wells

In the presence of an electric field the energy spectrum of a quantum well becomes continuous, with bound states transforming into resonances, but also with strong modifications in the above-barrier region. Analyzing the density of states (DOS) of the system, we find modulated oscillations of this quantity due to interference of the waves reflected from the well boundaries and from the slope of the electric-field potential. We show that these oscillations in DOS are related to the Fowler-Nordheim resonances in transmission through a double-barrier tunneling structure. We also calculate the absorption α(ħω) from the ground state in the well to the energy continuum above the barriers. We find a pronounced electric-field effect on α(ħω); the slowly varying curve for zero field transforms into a series of sharp peaks. The observation of these peaks requires narrow wells, wide barriers, and moderate electric fields. It would allow for the determination of important parameters like band offset or the value of the internal electric field.