High-speed InGaAs-based vertical Schottky barrier photodetectors

In this work, we report on the design, fabrication, and characterization of an InGaAs-based vertical Schottky barrier (VSB) photodetector that uses a lattice-matched n/sup -/-InAlAs Schottky barrier height enhancement layer in conjunction with a 320 nm-thick film of ITO to form a high quality transparent Schottky contact. The Schottky barrier height of ITO on n/sup -/-InAlAs was determined to be 0.68 eV through the use of Norde plots and I-V measurements. The thin film of ITO and the device passivation layer of silicon nitride, together, form an odd-multiple quarter-wave transformer to 1.31 /spl mu/m perpendicularly incident light. The devices exhibited very low dark current densities, high responsivities, and high 3-dB bandwidths. A dark current per unit area of 8.87 /spl middot/10/sup -5/ A/cm/sup -2/ at an applied bias of 5 V was obtained. The responsivity for all the devices tested ranged from 0.55 to 0.59 A/W at a wavelength of 1.31 /spl mu/m. The 15 /spl mu/m diameter devices exhibited 3-dB bandwidths of 19 and 25 GHz in response to 1.55 /spl mu/m illumination with an applied bias of 5 and 10 V, respectively.