Tunnel-Junction Layered Structure for Ohmic Contact on Ge
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Solution Overview
Problem
The fermi level pinning effect in n-type Ge substrates makes it challenging to form ohmic contacts, leading to increased resistance and losses in devices fabricated using III-V semiconductor materials, limiting the use of such substrates for growing III-V semiconductor layers.
Innovation Solution
A layered structure with a p-type semiconductor substrate and a tunnel junction layer, such as a n-on-p tunnel junction, is introduced to enable charge carriers to tunnel across the barrier, facilitating ohmic contacting and reducing resistance and losses, while maintaining low strain properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If n-type Ge substrates are used to grow III-V semiconductor layers, then the substrate can be doped to act as a low-resistance material, but the fermi level pinning effect prevents ohmic contacts from being easily formed, leading to increased resistance and losses
Solution Approach 1:
An n-type tunnel junction layer is introduced as an intermediary between the p-type substrate and the n-type semiconductor layers. This tunnel junction layer enables charge carrier tunneling across the p-n interface, effectively mediating the electrical connection and allowing ohmic contacting to be achieved without the fermi level pinning problem that would otherwise prevent it.
2Ease of manufacture
If a p-type substrate is used to avoid fermi level pinning, then ohmic contacts can be formed, but a p-on-n junction structure is required which may introduce additional complexity
Solution Approach 1:
The n-type tunnel junction layer serves as a mediator that enables the p-type substrate to function effectively with n-type device structures. By facilitating charge carrier tunneling, it allows the substrate to be contacted ohmically while maintaining compatibility with the n-type semiconductor layers, thus resolving the complexity issue.
3Stability of the object's composition
If III-V semiconductor materials are grown on group IV semiconductor substrates, then desirable low strain properties can be achieved, but the fermi level pinning effect in n-type Ge substrates limits their use
Solution Approach 1:
The substrate doping type is changed from n-type to p-type to eliminate the fermi level pinning effect. This parameter change allows III-V semiconductor materials to be grown on group IV substrates like Ge while achieving both desirable low strain properties and reliable device performance through ohmic contacting.
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
The tunnel junction layer allows for low-resistance and low-loss devices by enabling charge carrier tunneling across the barrier, reducing processing steps, and allowing for the use of p-type Ge substrates with low strain properties, thereby improving device performance.
Implementation Method 1
a tunnel junction layer between the substrate and the plurality of semiconductor layers... enables charge carriers to tunnel across the barrier
Data Source
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AI summary
The present disclosure relates to a layered structure (200, 300) comprising: a substrate (110) comprising a p-type semiconductor material; a plurality of semiconductor layers (120), on the substrate (110), comprising at least one p-on-n junction; and a tunnel junction layer (130) between the substrate (110) and the plurality of semiconductor layers.