Dopant migration effects in terahertz quantum cascade lasers.

We demonstrate that dopant migration and the resulting impurity scattering can strongly influence the performance of GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers. A nominally symmetric structure allows us to compare the negative and positive bias behavior of the very same device. Dopants, migrated towards the upper laser level during sample growth, degrade the lasing performance due to enhanced impurity scattering rates. The consequences are a higher threshold current (+30%) and reduced optical output power (-29%) in the affected operating direction. This polarity dependent performance is reversed in an asymmetrically doped sample, which imitates the migration of dopants against the growth direction. [ABSTRACT FROM AUTHOR]