Multilayer III-V Heterostructure Source/Drain for Leakage Control
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Solution Overview
Problem
Semiconductor devices face challenges in achieving low source/drain resistance and low contact resistance while minimizing unwanted channel leakage, particularly due to the limitations of using low effective mass materials which lead to off-state leakage and hot carrier effects.
Innovation Solution
A method involving a multilayer III-V heterostructure in the source/drain regions, comprising a bottom barrier layer, a seed layer, and a top layer with a compositionally graded layer, all made from compound semiconductor materials from Groups III and V of the Periodic Table, to reduce resistance and prevent leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low effective mass semiconductor materials (such as In(x)Ga(1−x)As) are used for the channel, then channel resistance is reduced, but off-state leakage and hot carrier effects increase
Solution Approach 1:
The source/drain regions are segmented into multiple layers with different bandgap characteristics. The bottom layer has a wider bandgap to prevent leakage, while the top layer has a narrower bandgap to reduce resistance, creating a segmented structure that resolves the contradiction between low resistance and low leakage
Solution Approach 2:
Different regions of the source/drain structure are assigned different material compositions with specific bandgap properties. The bottom portion uses wider bandgap materials for leakage prevention, while the top portion uses narrower bandgap materials for resistance reduction, applying local quality to different spatial regions
2Reliability
If materials with the smallest effective masses (e.g., InAs, Ge) are used, then contact resistance is improved and mobility is enhanced, but off-state leakage increases
Solution Approach 1:
The source/drain regions utilize composite material structures combining multiple III-V semiconductor compounds with different bandgap energies. This composite approach allows simultaneous achievement of low contact resistance (through narrow bandgap top layers) and low off-state leakage (through wide bandgap bottom layers)
3Reliability
If a single narrow bandgap material is used in source/drain regions, then contact resistance is reduced, but channel leakage increases
Solution Approach 1:
The solution transitions from a single-layer to a multi-layer vertical structure in the source/drain regions. This dimensional change allows the system to simultaneously achieve low contact resistance at the top interface and low channel leakage at the bottom interface by stacking materials with different bandgap properties
Data Source
AI summary
The source/drain of a fully III-V semiconductor or Si-based transistor includes a bottom barrier layer that may be lattice matched to the channel, a lower layer of a wide bandgap III-V material and a top layer of a comparatively narrow bandgap III-V material, with a compositionally graded layer between the lower layer and top layer gradually transitioning from the wide bandgap material to the narrow bandgap material.