Tunnel current in quantum dot infrared photodetectors

Infrared photodetectors have been fabricated based on InAs/GaAs self-assembled quantum dot (QD) layers, with various QD densities and doping levels. Dark currents have been measured as a function of applied bias and temperature. They show a clear activation energy, which decreases as the QD shell filling increases. Its absolute value and dependence on applied bias indicate that electrons tunnel from QD levels into the wetting layer of the next period. Resonant structures in the current–voltage curve and in its first derivative confirm the tunneling through the GaAs barrier. Negative differential resistances are observed in highly doped samples at low temperature.