Comparison of InGaAs pin photodiodes with Ti/Pt/Au and Au reflectors

The authors have fabricated planar InGaAs pin photodiodes designed for high-speed operation with rear metallic reflectors. The effectiveness of both Ti/Pt/Au and Au reflectors for enhancing the photoresponse of InGaAs pin photodiodes is evaluated. The experimental results show that an InGaAs pin photodiode with a 1 μm absorption layer can achieve a responsivity > 0.9 A/W (approx. 86% quantum efficiency) at 1.3 μm wavelength with an Au reflector but can achieve only approx. 0.8 A/W (approx. 76% quantum efficiency) with a Ti/Pt/Au reflector. Furthermore, the reflectivity of both metallic mirrors (approx. 0.9 for Au and approx. 0.4 for Ti/Pt/Au) is extracted using a simple theoretical model.