Description

Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge3H8 and SnD4 hydrides, to fabricate Ge1-ySny photodiodes with very high Sn concentrations in the 12%–16% range. A unique aspect of this approach is the compatible reactivity of the

Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge3H8 and SnD4 hydrides, to fabricate Ge1-ySny photodiodes with very high Sn concentrations in the 12%–16% range. A unique aspect of this approach is the compatible reactivity of the compounds at ultra-low temperatures, allowing efficient control and systematic tuning of the alloy composition beyond the direct gap threshold. This crucial property allows the formation of thick supersaturated layers with device-quality material properties. Diodes with composition up to 14% Sn were initially produced on Ge-buffered Si(100) featuring previously optimized n-Ge/i-Ge1-ySny/p-Ge1-zSnz type structures with a single defected interface. The devices exhibited sizable electroluminescence and good rectifying behavior as evidenced by the low dark currents in the I-V measurements. The formation of working diodes with higher Sn content up to 16% Sn was implemented by using more advanced n-Ge1-xSnx/i-Ge1-ySny/p-Ge1-zSnz architectures incorporating Ge1-xSnx intermediate layers (x ∼ 12% Sn) that served to mitigate the lattice mismatch with the Ge platform. This yielded fully coherent diode interfaces devoid of strain relaxation defects. The electrical measurements in this case revealed a sharp increase in reverse-bias dark currents by almost two orders of magnitude, in spite of the comparable crystallinity of the active layers. This observation is attributed to the enhancement of band-to-band tunneling when all the diode layers consist of direct gap materials and thus has implications for the design of light emitting diodes and lasers operating at desirable mid-IR wavelengths. Possible ways to engineer these diode characteristics and improve carrier confinement involve the incorporation of new barrier materials, in particular, ternary Ge1-x-ySixSny alloys. The possibility of achieving type-I structures using binary and ternary alloy combinations is discussed in detail, taking into account the latest experimental and theoretical work on band offsets involving such materials.

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Title
  • Direct Gap Ge1-ySny Alloys: Fabrication and Design of Mid-IR Photodiodes
Date Created
2016-07-13
Resource Type
  • Text
  • Collections this item is in
    Identifier
    • Digital object identifier: 10.1063/1.4956439
    • Identifier Type
      International standard serial number
      Identifier Value
      0021-8979
    • Identifier Type
      International standard serial number
      Identifier Value
      1089-7550
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    Senaratne, C. L., Wallace, P. M., Gallagher, J. D., Sims, P. E., Kouvetakis, J., & Menéndez, J. (2016). Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes. Journal of Applied Physics, 120(2), 025701. doi:10.1063/1.4956439

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