HEMT LDD Formation via Polarization-Graded Channel Supplying Layer
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Solution Overview
Problem
High electron mobility transistors (HEMTs) face challenges in maintaining high breakdown voltage due to electron concentration variations in 2DEG channels, making it difficult to reliably form lightly doped drain (LDD) regions with consistent electron concentration.
Innovation Solution
The HEMT design includes a channel supplying layer with semiconductor layers of varying polarizabilities, an etching buffer layer, and a recessed portion to form a 2DEG channel, which helps in reducing electron concentration variations and ensuring reliable LDD region formation by using an etching buffer layer that also supplies the channel, thereby increasing the margin for etching operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional HEMT structures are used, then high electron mobility is achieved, but breakdown voltage decreases due to electron concentration variations in 2DEG channels
Solution Approach 1:
The channel supplying layer is divided into multiple semiconductor layers with different polarizabilities (e.g., AlN layer with higher polarizability and GaN layer with lower polarizability). This segmentation allows independent optimization of each layer's contribution to 2DEG formation, enabling control over electron concentration distribution to maintain high mobility while preventing breakdown voltage degradation.
Solution Approach 2:
Different regions of the channel supplying layer are assigned different material compositions and polarizabilities. The AlN layer provides high polarizability for strong 2DEG formation in regions requiring high electron mobility, while the GaN layer provides lower polarizability to modulate electron concentration in regions where breakdown voltage must be maintained, creating spatially varying local properties.
2Reliability
If LDD regions are formed to maintain breakdown voltage, then electron concentration control becomes difficult due to variations in 2DEG channels
Solution Approach 1:
The channel supplying layer with controlled polarizability gradient is formed beforehand to pre-establish the desired electron concentration distribution in the 2DEG channel. This preliminary structuring of the channel region enables subsequent LDD region formation to proceed with better control over electron concentration, as the base channel already has optimized carrier distribution that compensates for doping variations.
Solution Approach 2:
The polarizability parameter of the channel supplying layer is systematically varied through material composition changes (AlN to GaN transition). This parameter change creates a controlled gradient in electron concentration across the channel, which serves as a foundation for forming LDD regions with more consistent electron concentration, reducing manufacturing variability.
3Ease of manufacture
If etching buffer layer is used to form recessed portion, then manufacturing margin increases, but process complexity increases
Solution Approach 1:
The AlN layer serves dual functions: it acts as an etching buffer layer that provides a controlled stop during recess formation to ensure manufacturing precision, and simultaneously functions as a high-polarizability channel supplying layer that contributes to 2DEG formation. This multi-functionality increases manufacturing ease without proportionally increasing device complexity, as the same layer structure achieves both process control and electrical performance.
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 enhances the reliability and reproducibility of LDD regions, maintaining high breakdown voltage and improving the on-current of HEMTs by controlling electron concentration and reducing gate leakage.
Implementation Method 1
The channel supplying layer includes a plurality of semiconductor layers having different polarizabilities
Data Source
AI summary
High electron mobility transistors (HEMTs) including lightly doped drain (LDD) regions and methods of manufacturing the same. A HEMT includes a source, a drain, a gate, a channel supplying layer for forming at least a 2-dimensional electron gas (2DEG) channel, and a channel formation layer in which at least the 2DEG channel is formed. The channel supplying layer includes a plurality of semiconductor layers having different polarizabilities. A portion of the channel supplying layer is recessed. One of the plurality of semiconductor layers, which is positioned below an uppermost layer is an etching buffer layer, as well as a channel supplying layer.