Current induced intersubband absorption in GaAs/GaAlAs quantum wells

The observation of intersubband (e1-e2) absorption induced by current injection in GaAs/GaAlAs multiquantum wells is reported. The new technique enables sensitive measurement of intersubband transitions in undoped quantum wells. The carrier concentration in the wells is easily controlled by varying the current density. The technique is demonstrated on undoped multiquantum well layers sandwiched in a p-i-n laser-diodelike structure. The lowest confined level was populated by biasing the junction and hence injecting carriers into the quantum wells. The spectra were taken by a Fourier transform infrared (FTIR) spectrometer, modulating the current and using the double modulation method. The dependence of the absorption on current intensity was examined and excess carrier concentration and lifetime were calculated. The induced absorption saturates at current densities higher than 100 mA/cm².