The Dual-Heterojunction Ge on Si Photodetector

Metal contact plugs are today commonly used to establish electrical connection to the anode and cathode electrodes of Ge on Si integrated photodetectors. While large progress has been made in optimizing these contacts, scattering loss at the metal regions still remains the most important efficiency-limiting factor. In addition, the process used to form the contacts is challenging because of the relatively high attack rate of Ge in aqueous solutions. In this paper an alternative way of building and contacting a Ge diode is presented: leveraging the presence of the Si substrate, highly doped n- and p-type regions are formed on the sides of the Ge region. These both serve establishing the built in potential in the diode as well as offering a low resistance path for the photocurrent extraction. Devices built using this approach match and sometime exceed the performance of the classic “PIN” homojunction ones. In this paper experimental results from a number of dual heterojunction Ge on Si devices based on the LuxG process (Luxtera’s integrated sislicon photonic process) will be presented and discussed.