Optoelectronic semiconductor device

Abstract

An optoelectronic semiconductor device includes a first cladding layer (1) of the first conductivity type provided on a substrate (11), an active layer (2), a second cladding layer (3) of a second conductivity type, an intermediate layer (4), and a third cladding layer (5) also of the second conductivity type, the thickness of the second cladding layer (3) being such that the intermediate layer (4) lies within the optical field profile of the active layer (2), while the intermediate layer (4) includes a semiconductor material with a lower bandgap than the second (3) and third (5) cladding layers. Such devices, often in the form of diode lasers, are used inter alia in optical glass fibre communication and optical disc systems. A disadvantage of such devices is that their starting currents are comparatively high. The semiconductor material of the intermediate layer (4) has a lattice constant which is different from that of the substrate (11 ) and a bandgap which is greater than the energy of the radiation emitted by the active layer (2). As a result, the simplest possible semiconductor materials may be chosen for the intermediate layer (4), which materials have a low absorption for the emitted radiation. The starting current is reduced by this and a comparatively thick intermediate layer (4) can be used, which favors its use as an etching stopper layer. These advantages are particularly realised in devices comprising a mesa (20), such as ridge-type lasers. Ternary semiconductor materials such as InGaAs and InGaP in that case form very suitable materials for the intermediate layer (4).