Enhancement of Absorption Magnitude of Short-Wavelength Intersubband Transition in InGaAs/AlAs Quantum Wells

Reduction of absorption magnitude with shortening of the intersubband transition wavelength is observed in InGaAs/AlAs quantum wells on GaAs substrates. Theoretical calculation of the carrier distribution shows that the reduction is caused by carrier leakage to the X minimum of the AlAs barrier from the Γ minimum of the InGaAs well. In order to regain the absorption magnitude, we undertake to suppress the carrier leakage by reducing the density of states in the AlAs X minimum and by increasing the energy spacing between Γ and X minima. The optimizations lead to the enhancement of the absorption magnitude of more than fourfold, and a peak absorption coefficient of 14000 cm -1 is obtained with an optimized structure. The results obtained here are considered very useful for device applications of the short-wavelength intersubband transitions.