Two-Valued Characteristics in Semiconductor Quantum Well Lasers

Due to internal optical absorption loss, which varies with carrier density in the optical confinement region, the operating characteristics can be two valued in semiconductor quantum well lasers. Particularly, there can be two lasing thresholds and two branches in the light-current characteristic. While the internal differential quantum efficiency for the first (conventional) branch of the light-current characteristic is less than 1 and decreases with increasing pump current, that for the second (unconventional) branch is greater than 1 and nonmonotonous.