Reduction of 1/f carrier noise in InGaAsP/InP heterostructures by sulphur passivation of facets

The influence of facet passivation on the noise behaviour of InGaAsP/InP double-heterostructures used for laser diodes is investigated. The facet treatment with sodium sulphide resulted in a reduction of the low-frequency noise by about 30 dB (at 1 kHz). This noise reduction can clearly be attributed to the decrease of the surface state density by facet passivation. Moreover, our measurements indicate that the strong 1/f carrier noise in InGaAsP/InP semiconductor laser diodes is essentially caused by surface recombination.