Measurement of Photon Absorption Loss in the Active and Passive Regions of a Semiconductor Laser

A technique is described for measuring the photon absorption coefficients in the active and passive regions of an electron-beam-pumped semiconductor laser. Measurements made at 4°K on n-type, single-crystal GaAs indicate that photon loss in the active region is due to free carrier absorption, and that this absorption coefficient increases linearly from 2.5 cm−1 to 47 cm−1 as donor concentration is varied from 2.4 × 1017 cm−3 to 4.7 × 1018 cm−3. For each case the active region absorption coefficient is less than that measured in the passive region, which varies from 354 cm−1 to 98 cm−1 over the same range of donor concentrations. The increased loss in the passive region is attributed to interband absorption transitions.