Conservation of low dark current of InGaAs photodiodes after NH3/HF etch with a BCB passivation layer

Investigations on the effect of a BCB (benzocyclobutene) coating of InGaAs photodiodes are performed. Samples with two different layer structures are used for fabricating mesa diodes using wet and dry etching. It is found that simple spin-on of BCB reduces surfaces damages of the diode sidewalls caused by plasma processing significantly. The combination of wet etching and BCB coating yields excellent dark current densities of 2 mu A/cm2 and 3.5 mu A/cm2 at 2 V reverse bias for samples with and without an intermediate quaternary layer on the p-side, respectively. Furthermore the BCB coating functions as a protection against surface degradation in subsequent plasma processes, and is a good candidate for a long term passivation.