GaN HEMT Regrown Source-Drain Contacts for Lower Ohmic Resistance
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Solution Overview
Problem
The reduction of ohmic contact resistance in GaN-based HEMTs is limited due to GaN's wide band gap and high resistance, which restricts the expansion of high frequency operation bands, and regrowing semiconductor materials like GaAs faces challenges due to lattice-mismatch and crystal structure differences.
Innovation Solution
A manufacturing method involving the growth of nitride semiconductor barrier and channel layers on a first substrate, followed by bonding to a nitrogen-free second substrate, forming grooves, and regrowing semiconductor regions with impurities to reduce contact resistance, allowing for lower resistance ohmic connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ohmic electrodes are formed directly on GaN layer, then the structure is simple, but contact resistance is high due to GaN's wide band gap and high resistance
Solution Approach 1:
The patent employs a composite material structure consisting of GaN-based nitride semiconductor layers (channel layer and barrier layer) combined with a regrown semiconductor layer (such as GaAs or InP) that has been heavily doped with impurities. This composite structure allows the device to leverage the high breakdown voltage characteristics of GaN while achieving low contact resistance through the regrown layer, which has different electrical properties that facilitate better ohmic contact.
2Reliability
If semiconductor material like GaAs is regrown to reduce contact resistance, then contact resistance decreases, but lattice-mismatch and crystal structure differences cause growth difficulties
Solution Approach 1:
The patent utilizes parameter changes by heavily doping the regrown semiconductor layer with impurities at high concentrations (1×10^19 to 1×10^21 atoms/cm³). This extreme doping parameter transformation fundamentally alters the electrical properties of the regrown layer, reducing its resistance by several orders of magnitude and enabling effective ohmic contact despite the inherent difficulties of regrowing lattice-mismatched materials.
3Device complexity
If AlGaN layer is used for ohmic contact, then the structure is simple, but contact resistance is high due to AlGaN's larger band gap and higher resistance than GaN
Solution Approach 1:
The patent introduces a regrown semiconductor layer as an intermediary between the metal electrode and the GaN channel layer. This intermediary layer, which is heavily doped with impurities, serves as a resistance-reducing bridge that facilitates current flow from the electrode to the channel, overcoming the high resistance problem of direct AlGaN or GaN contacts while maintaining structural simplicity.
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 decreases the contact resistance of source and drain electrodes, enabling further extension of high frequency characteristics and broadening the frequency band of GaN-based HEMTs.
Implementation Method 1
a buffer layer 302 formed by epitaxial growth, a channel layer 303, and a barrier layer 304 are layered sequentially on a substrate 301
Implementation Method 2
The nitride semiconductor has a crystal structure of hexagonal crystal and has a polarization in the c-axial direction. Due to effects of this polarization, a heavily concentrated sheet carrier (two-dimensional electron gas) at approximately 10^13 cm^-3 is spontaneously formed by forming a heterojunction between AlGaN and GaN
Implementation Method 3
forming, in the first groove and the second groove, a source region and a drain region in contact with the channel layer by regrowing a semiconductor with no nitrogen contained in which impurities are injected
Data Source
AI summary
A first regrowth layer and a second regrowth layer comprising GaAs having high resistance are regrown on a surface of an etching stop layer exposed to the bottom of a first groove and a second groove, and then n-type InGaAs is regrown on the first regrowth layer and the second regrowth layer, whereby a source region and a drain region configured to make contact with a channel layer are formed in the first groove and the second groove respectively.