A semiconductor laser element is specified in Japanese Patent Publication No. 2002-299763 A.
On account of their compactness and cost-effective production, semiconductor laser diodes are used in numerous areas of application, such as, for example, data transmission, data storage, projection, material processing, optical pumping, biosensor technology and the like. In particular semiconductor laser diodes having a ridge waveguide, so-called ridge laser diodes, are used in this case. Conventional ridge technology is encountering its limits here in the face of constantly increasing requirements regarding higher powers, improved mode behavior and the like, with regard to robustness, reliability and high radiation efficiency. Central problems here are the inadequate mechanical stability, the deficient electrical loading capacity and the unsatisfactory leakage current and aging behavior of the conventional ridge laser diodes. In particular, the manufacturing yield for mass market applications and the production costs associated therewith are not optimal.
FIGS. 6A and 6B illustrate two exemplary embodiments of a conventional ridge waveguide semiconductor laser diode in cross section. On a GaN substrate 100 there are arranged an n-conducting cladding layer 101, an n-conducting waveguide layer 102, an active semiconductor layer 2c, a p-conducting waveguide layer 103, a p-conducting cladding layer 104 and an ohmic contact layer 105. The p-conducting cladding layer 104 and the p-conducting waveguide layer 103 are etched in such a way that a ridge waveguide 200 is formed. The semiconductor laser diode thus has a main body 201 and a ridge waveguide 200.
Side faces of the ridge waveguide and of the main body are provided with a passivation layer 107. In this case, the passivation layer 107 is arranged uniformly on the side faces, such that this is embodied in a stepped fashion. In addition, the passivation layer has an opening on the surface of the ridge waveguide, such that an electrical contact connection is made possible at this surface of the ridge waveguide.
For making electrical contact with the semiconductor laser diode, an n-conducting connection layer 106 is arranged on that side of the substrate which faces away from the semiconductor layers and a p-conducting connection layer 5 is arranged on the passivation layer and the ridge waveguide.
However, laser diodes of this type have a deficient robustness since the ridge waveguide of the laser diode is susceptible to mechanical damage such as, for example, scratching, bond damage or external mechanical force effects. In addition, on account of the vertically formed side face of the ridge waveguide, uniform application of the p-side contact is difficult to carry out since, on account of shading effects, the contact feed at the base of the ridge waveguide is formed in a very thin fashion. However, these thinned contact regions constitute weak points in the current-carrying capacity and can lead to an electrical failure of the semiconductor laser diode. A further problem of the conventional laser diodes is a short-circuit risk. In particular on account of the passivation layer 107 having a thickness of only a few 100 μm, there is the risk of a short circuit in the region of the active layer 2c in the case where the etching process carried out for producing the ridge waveguide is implemented partially deeper, such that etching is effected near or even through the active layer 2c.