Broadband PureB Ge photodiodes fabricated on highly doped n+-Si for operation down to 0 V

PureB Ge-on-Si photodiodes were fabricated on silicon wafers highly-doped (HD) with arsenic to more than 1019 cm−3. As compared to diodes previously fabricated on wafers lightly-doped (LD) with phosphorus to 1015 cm−3, the operation voltage was shifted from a high reverse bias of 15 to 20 V to the 0 to 2 V region. The Ge was grown at 700 °C by chemical-vapor deposition to selectively fill windows in 3.5-μm-thick oxide. They were capped in-situ, also at 700 °C, with a 10-nm-thick pure boron layer to form the p-type anode region. Near-ideal responsivities of 0.21, 0.28, 0.64, and 0.57 A/W were obtained at 406, 670, 1310 and 1550 nm wavelengths respectively, in spite of relatively high defect densities related to a significant degree of arsenic autodoping. For the first, the high arsenic concentration at the Ge-Si interface eliminated the influence of a p-type interfacial potential barrier that otherwise impeded the detection of photogenerated carriers in photodiodes fabricated on LD substrates. In addition, the arsenic autodoping of the Ge resulted in a doping gradient and associated electric field that aided in the separation and detection of carriers photogenerated in the non-depleted Ge.