Matching Items (2)

128050-Thumbnail Image.png

Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

Description

Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge[subscript 3]H[subscript 8] and SnD[subscript 4] hydrides, to fabricate Ge[subscript 1-y]Sn[subscript y] photodiodes with very high Sn concentrations in

Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge[subscript 3]H[subscript 8] and SnD[subscript 4] hydrides, to fabricate Ge[subscript 1-y]Sn[subscript y] 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-Ge[subscript 1-y]Sn[subscript y]/p-Ge[subscript 1-z]Sn[subscript z] 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-Ge[subscript 1-x]Sn[subscript x]/i-Ge[subscript 1-y]Sn[subscript y]/p-Ge[subscript 1-z]Sn[subscript z] architectures incorporating Ge[subscript 1-x]Sn[subscript x] 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 Ge[subscript 1-x-y]Si[subscript x]Sn[subscript y] 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.

Contributors

Agent

Created

Date Created
  • 2016-07-13

129304-Thumbnail Image.png

Electroluminescence from GeSn heterostructure pin diodes at the indirect to direct transition

Description

The emission properties of GeSn heterostructure pin diodes have been investigated. The devices contain thick (400–600 nm) Ge [subscript 1− y] Sn [subscript y] i-layers spanning a broad compositional range below

The emission properties of GeSn heterostructure pin diodes have been investigated. The devices contain thick (400–600 nm) Ge [subscript 1− y] Sn [subscript y] i-layers spanning a broad compositional range below and above the crossover Sn concentration y [subscript c] where the Ge [subscript 1− y] Sn [subscript y] alloy becomes a direct-gap material. These results are made possible by an optimized device architecture containing a single defected interface thereby mitigating the deleterious effects of mismatch-induced defects. The observed emission intensities as a function of composition show the contributions from two separate trends: an increase in direct gap emission as the Sn concentration is increased, as expected from the reduction and eventual reversal of the separation between the direct and indirect edges, and a parallel increase in non-radiative recombination when the mismatch strains between the structure components is partially relaxed by the generation of misfit dislocations. An estimation of recombination times based on the observed electroluminescence intensities is found to be strongly correlated with the reverse-bias dark current measured in the same devices.

Contributors

Agent

Created

Date Created
  • 2015-03-02