Ohmic Contacts With Ultra-Low Optical Loss on Heavily Doped n-Type InGaAs and InGaAsP for InP-Based Photonic Membranes

In this paper, we present significant reductions of optical losses and contact resistances in AgGe-based ohmic contacts to InP membranes. Due to the high solubility of Si in InGaAs and InGaAsP, heavily doped n-type contact layers are grown on InP wafers. This high doping concentration gives rise to annealing-free ohmic contacts and low contact resistances at the level of 10
^-7
Ω cm
²
. It also leads to strong band-filling effects in InGaAs and InGaAsP, which result in low optical absorption losses in the contact layer. Combined with the low optical loss of AgGe, a massive reduction of the propagation loss in membrane waveguides is observed compared with other existing solutions. An additional advantage is the minimal influence of thermal treatments during the processing, leading to very stable high-performing contacts.