MEASUREMENT OF PHOTON ABSORPTION LOSS IN THE ACTIVE AND PASSIVE REGIONS OF A SEMICONDUCTOR LASER

Abstract

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.