MBE-deposited iridium silicides for focal plane array applications

Abstract

Iridium silicides are of current interest as candidate detector materials for silicon based, Schottky-barrier infrared focal plane arrays. In this work, the growth and structure of codeposited IrSi₃ and Ir₃Si₄ films is discussed as well as the effect of annealing and deposition temperature on pure Ir film depositions. Nearly single-phase polycrystalline IrSi₃ films were formed by codeposition of Ir and Si in a 1:3 ratio at temperatures as low as 450°C. Localized epitaxial crystallite growth, identified by x-ray and electron diffraction, is found for IrSi₃ films formed at temperatures >600 °C, with a previously unreported c-axis epitaxial crystallite growth on Si(111) dominating at ∼700 °C. Single-phase polycrystalline Ir₃Si₄ films were formed by annealing room temperature 3:4 codeposited films, whereas localized epitaxial Ir₃Si₄ crystallite growth occurred for codeposition at temperatures of ∼500 °C. Annealed Ir films initially form IrSi crystallites at temperatures of ∼350 °C and further react with the substrate to form polycrystalline Ir₃Si5 at temperatures ≥ 550 °C. The Ir₃Si₄ phase, not found in annealed reactions, dominated the growth of silicide films formed by hot Ir depositions at 500 °C. A previously unreported Ir₃Si₄ epitaxial growth was identified for Ir depositions on Si(111)substrates. Resistivity measurements indicate that IrSi₃, IrSi, and Ir₃Si₄ films are metallic, where Ir₃Si₄ had the lowest resistivity of ∼60 μΩ-cm. Optical photoresponse and I-V measurements performed on diode structures indicate the barrier height of IrSi₃ on p-type Si(111) (∼0.33 eV) to be higher than that on p-type Si(100) (∼0.22-0.25 eV), limiting infrared imaging capability to the SWIR (1-3 μm) and MWIR (3-5 μm) atmospheric transmission windows, respectfully. Codeposited Ir₃Si₄ films display optical barrier heights between 0.125 to 0.175 eV on p-type Si(100), providing possible imaging capability in the LWIR (8-12 μm) spectral region. Ir₃Si₄ devices, displaying localized epitaxial crystallite growth, yield higher emission efficiency than polycrystalline Ir₃Si₄ films. Optical photoresponse measurements on a IrSi device also indicate a low optical barrier height (∼0.12 eV) providing access to the LWIR spectral region. Optical measurements on Ir₃Si5 films are also presented.