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Modeling and Simulation Study of Electrical Properties of Ge-on-Si Diodes with Nanometer-thin PureGaB Layer

Deposition of a nanometer-thin layer-stack of pure gallium and boron (PureGaB) on arsenic (As)-doped epitaxial germanium (Ge) forms a shallow-junction photodiode, reported to have almost ideal I-V characteristics, low saturation current densities, and high responsivity down to 255 nm wavelengths. In this work, different physical mechanisms that could explain the high anode Gummel number in PureGaB-Ge-on-Si diode have been examined. A model for point-defect-mediated diffusion of B and Ga in Ge has been developed. Formation of a shallow pn junction has been modeled using 1D process simulations of B and/or Ga drive-in from the PureGaB layer. B diffusion resulted in junction depths less than a nanometer deep, while Ga formed a highly doped p+ regions with peak concentrations> 10 20 cm −3 and junction depths from 31 nm to 123 nm, depending on the applied sets of diffusion parameter. Both approaches have been used to fit the I-V characteristics of a fabricated PureGaB Ge-on-Si diode: B-only diffusion model with negative interface charge concentration of 1.9 10 13 cm −2 for suppression of electron injection and Ga diffusion model, self-sufficient for the explanation of low electron current densities. Both proposed models give possibilities to obtain a Gummel number of ≈ 2×10 14 s/cm 4 , matching the value extracted from I-V characteristics of a fabricated device.

PureGaB ; Ge-on-Si ; germanium ; detector ; infrared ; gallium ; boron ; diffusion ; process simulations ; anode Gummel number ; interface charge layer

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