| The systematic development of a S passivation process for application in AlxGa1-xAs high power lasers is discussed. The treatment process consisted of a wet chemical etch, and a low damage dielectric coating using Electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) technique. Its effectiveness in controlling non-radiative recombination near the surface of a series of AlxGa1-x As epitaxial structures was determined by photoluminescence (PL) and photoreflectance (PR) measurements. Nominally undoped, low x treated surfaces showed large PL enhancements, while the thick native oxides of high x surfaces rendered the treatment less effective. PR measurements indicated a reduction in the surface electric field in p-type materials, and increased band bending in n-type materials which was consistent with a passivation model. Initial application of the treatment process to laser diodes highlighted problems, as determined mainly by light output versus current tests. A decrease in the output power and an increase in threshold current after treatment was attributed to diffierential etching of the epitaxial layers in the S solution, and facet microroughness due to the pre-etch. However, under appropriate processing conditions, high power lifetime tests s how an improvement in reliability with treated lasers showing an average ∼0.14% degradation compared to ∼34% for "as is" lasers. |
