GeSn Intermetallic Contacts Without Tin Segregation
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Solution Overview
Problem
Existing methods for creating ohmic contacts in microelectronic or optoelectronic devices containing germanium-tin (GeSn) alloys risk segregating tin, leading to ineffective light sources or photodetectors, especially when the tin concentration exceeds 1% and during high-temperature processing.
Innovation Solution
A method involving epitaxy of a GeSn layer on a growth layer, forming an active region, removing part of the growth layer to reduce surface contact, and then heating in a furnace to create an intermetallic compound with low resistivity, while controlling the surface extent and bearing surface areas to prevent tin segregation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heating is applied to create an intermetallic compound for low-resistivity ohmic contact, then electrical conductivity is improved, but tin segregation occurs leading to loss of optoelectronic functionality
Solution Approach 1:
The patent applies preliminary action by performing a first annealing treatment at a moderate temperature (200-400°C) before the main heating step to create an intermetallic compound layer. This preliminary action prepares the structure to withstand subsequent high-temperature processing without tin segregation, as the pre-formed intermetallic layer acts as a protective barrier during the second heating step that achieves low resistivity.
2Manufacturing precision
If high temperature processing is used to form intermetallic compound, then contact resistivity is reduced, but tin atoms leave the crystal lattice causing segregation
Solution Approach 1:
The patent segments the heating process into two distinct stages: a first annealing step at moderate temperature (200-400°C) to form the intermetallic compound layer, and a second heating step at higher temperature to reduce resistivity. This segmentation allows each step to be optimized independently, achieving low contact resistivity while preventing tin segregation through the protective intermetallic layer formed in the first stage.
3Reliability
If tin concentration in GeSn alloy is increased to improve optoelectronic performance, then light emission/absorption efficiency is enhanced, but tin segregation becomes more pronounced during heating
Solution Approach 1:
The patent applies preliminary action by performing a first annealing treatment at a moderate temperature (200-400°C) before the main heating step to form an intermetallic compound layer. This pre-formed intermetallic layer acts as a protective barrier during subsequent high-temperature processing, preventing tin atoms from leaving the crystal lattice even when tin concentration exceeds 1%, thereby maintaining both high optoelectronic performance and compositional stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively creates an ohmic contact with low resistivity without segregating tin in the active region, even at high tin concentrations, thereby preserving the integrity and functionality of the optoelectronic devices.
Implementation Method 1
a method involving epitaxy of a GeSn layer on a growth layer
Implementation Method 2
heating in a furnace to create an intermetallic compound
Implementation Method 3
a process of diffusion and/or inter-diffusion and/or nucleation involving atoms of the metal
Implementation Method 4
Most of the energy of the beam is absorbed by the layer of TiN and the heat diffuses towards the layers of Ni and of GeSn
Data Source
AI summary
The method of the invention comprises an epitaxy of a layer of interest made of GeSn on a growth layer comprising Ge, having a concentration of tin lower than that of the layer of interest; a formation of an active region in the layer of interest, having a surface extent smaller than a first maximum surface area; a removal of a part of the growth layer so that the interface between the growth layer and the layer of interest facing the active region is less than a second maximum surface area or null; a formation of a metallic portion including Ti or NiPt on a part of the layer of interest;a heating in a furnace to a temperature strictly greater than the epitaxy temperature, to create an intermetallic compound from the metallic portion; the first and second maximum surface areas being such that the tin in the active region does not segregate.