Colloidal Germanium Inks for 3D Printed Semiconductors

The intrinsic properties of Ge, such as favorable band gap, high extinction coefficient, tunable optical properties and high carrier mobilities result in advantageous charge transport properties making them an ideal candidate for applications in photodetectors, bioimaging, energy conversion and storage devices. These properties can be enhanced upon the incorporation of dopants to further alter these properties via tuning of the band structure. Current research has focused on group III and V elements as dopants, but the use of transition metals has yet to be explored. We report a generalized and low temperature synthesis of transition metal (Cu, Mn, Ni, and Co) doped Ge nanoparticles (NPs) under ambient conditions. By varying the metal and concentration used during the synthesis, the optical absorption of the Ge NPs can be tuned between the range of 330 and 430 nm, These colloidal particles can be readily utilized as an ink for additive manufacturing and the ability to sinter the printed particles is demonstrated using both thermal and photonic processes. The effect that doping the colloidal Ge NPs has on the electro-optic properties of the printed films is also explored with a wide range of tunable conductivities reported. Finally, devices were fabricated to investigate the change in the electrical conductivity of the printed Ge films upon exposure to light and an increase of nearly 3 orders of magnitude was measured.