Perforating Ohmic Contact for GaN Semiconductor Layers
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Solution Overview
Problem
Forming effective ohmic contacts, particularly for p-type GaN, is challenging due to high activation energy of acceptors and difficulty in finding metals with a suitable work function, leading to high contact resistivity and short channel effects in semiconductor devices.
Innovation Solution
A perforating ohmic contact is created by forming a set of metal protrusions that penetrate the semiconductor layer, with the characteristic length scale and annealing conditions optimized based on the sheet resistance and contact resistance, enhancing field emission or field-enhanced thermionic emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ohmic contact methods (annealing or recessed contacts) are used, then contact formation is achieved, but high contact resistivity and short channel effects occur
Solution Approach 1:
The contact structure is segmented into multiple components: a recessed cavity in the semiconductor layer, metal protrusions extending into the cavity, and a planar metal layer filling the cavity. This segmentation allows each component to perform its specific function - the recessed cavity provides access to the 2DEG, the metal protrusions establish ohmic contact, and the planar layer provides current distribution, thereby achieving low contact resistivity while maintaining device simplicity
Solution Approach 2:
The invention transitions from a conventional planar contact to a three-dimensional recessed contact structure with metal protrusions extending vertically into the semiconductor layer cavity. This dimensional change enables the contact to access the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface, significantly reducing contact resistivity by establishing direct ohmic contact with the high-carrier-density region
2Reliability
If the contact area is increased to reduce contact resistance, then current crowding increases and device performance deteriorates
Solution Approach 1:
The contact structure segments the current path into vertical flow through metal protrusions into the 2DEG and lateral distribution through the planar metal layer. This segmentation allows the contact area to be effectively increased for low contact resistance while the recessed cavity geometry distributes current uniformly, preventing current crowding at the contact periphery
Solution Approach 2:
The recessed cavity acts as an intermediary structure between the metal contact and the semiconductor surface. It provides a controlled geometry that guides current flow vertically into the 2DEG through metal protrusions, then distributes it laterally through the planar metal layer, thereby reducing contact resistance without creating current crowding effects
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 approach results in lower contact resistivity and reduced current crowding, improving device performance by increasing the contact area and perimeter of the ohmic electrode, effectively addressing the limitations of conventional ohmic contacts.
Implementation Method 1
enhancing field emission or field-enhanced thermionic emission
Implementation Method 2
enhancing field emission or field-enhanced thermionic emission
Implementation Method 3
annealing the semiconductor structure and the metal using a set of conditions configured to ensure formation of the set of metal protrusions
Data Source
AI summary
A perforating ohmic contact to a semiconductor layer in a semiconductor structure is provided. The perforating ohmic contact can include a set of perforating elements, which can include a set of metal protrusions laterally penetrating the semiconductor layer(s). The perforating elements can be separated from one another by a characteristic length scale selected based on a sheet resistance of the semiconductor layer and a contact resistance per unit length of a metal of the perforating ohmic contact contacting the semiconductor layer. The structure can be annealed using a set of conditions configured to ensure formation of the set of metal protrusions.