THEORETICAL-STUDY OF DIFFERENTIAL GAIN IN STRAINED QUANTUM-WELL STRUCTURES

Differential gain in semiconductor lasers is closely related to high-frequency capability, and the modulation band-width is expanded with enhancement of the differential gain. In this paper, the differential gain expected in a strained quantum well (QW) and in a lattice-matched QW is discussed based on a theoretical treatment of the band structures where the band nonparabolicity is taken into account. The differential gain in strained QW's will be larger by about three-four times relative to lattice-matched QW's, and a maximum differential gain of 4-6 x 10(-15) cm2 will be possible in strained QW's. The anisotropy of the subband nonparabolicity in lattice-matched QW's contributes to the larger difference between the two types of QW's. The calculated band-edge effective masses and the calculated laser properties are compared to the available measurements, and some comments are given for realizing high-speed strained lasers.