Injection lasers made from graded-interface GalnAsP/lnP heterostructures

Heterostructures based on GalnAsP/lnP with a graded-interface heterojunction have been developed. Examination by metallography, electron microprobe analysis, and electroluminescence shows that the graded-interface layer is at the boundary between the active layer and the upper epitaxial layer of InP. The charge in the gap width over the layer thickness lies in the interval Δ E_g/Δ L=0.08–0.01 eV/μm for the various structures. The size of the graded layers varies from 0.5 to 1.2 μm in the various structures. These figures are smaller than the diffusion length of the injected carriers. Band schemes are given for two types of structures which have been developed: a p-InP-p-GaInAsP-n-InP structure and a p-InP-n-GaInAsP-n-InP structure. The mechanism for the transport of injected carriers and the influence of the graded layer on these carriers are discussed. The heterostructures have been used to fabricate lasers which operate at wavelengths of 1.08–1.095 μm at room temperature. These characteristics of these lasers have been studied. Their output characteristics are not surpassed by those of heterostructure lasers fabricated from sharp GalnAsP/lnP heterostructures (at the same wavelengths).