Epitaxial Substrate With Gradient In Barrier Layer
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Solution Overview
Problem
Existing semiconductor devices face challenges in achieving improved ohmic contact characteristics between electrodes and barrier layers, leading to reduced power density and efficiency, as well as reliability and cost concerns in high-frequency/high-power applications.
Innovation Solution
A semiconductor device with an epitaxial substrate featuring a barrier layer with a gradient composition, where the In composition ratio increases towards the surface, enhancing ohmic contact characteristics and two-dimensional electron gas concentration, is developed. The barrier layer has a near-surface portion with a higher In composition ratio than the base portion, optimized for improved contact resistance and device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a barrier layer with uniform composition is used, then the manufacturing process is simple, but the ohmic contact characteristics are poor
Solution Approach 1:
The barrier layer is designed with non-uniform In composition ratio, where the near-surface portion has a higher In composition ratio than the base portion. This local variation in composition improves ohmic contact characteristics at the surface while maintaining the necessary barrier properties in the bulk, resolving the contradiction between contact quality and structural simplicity.
Solution Approach 2:
The In composition ratio parameter is changed across the barrier layer thickness, creating a gradient structure. This parameter variation optimizes the electronic properties at different depths, improving ohmic contact characteristics without requiring complex multi-layer structures.
2Reliability
If the In composition ratio is increased to improve ohmic contact, then contact resistance decreases, but the lattice strain increases
Solution Approach 1:
The In composition ratio is locally increased only in the near-surface portion of the barrier layer, rather than uniformly throughout. This localized composition optimization reduces contact resistance at the critical interface while limiting lattice strain to a specific region, preventing excessive overall strain in the structure.
Solution Approach 2:
The In composition ratio is partially increased in the near-surface portion rather than throughout the entire barrier layer. This partial action achieves the necessary contact improvement without applying excessive In content that would cause unacceptable lattice strain in the bulk material.
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 gradient composition in the barrier layer significantly improves ohmic contact characteristics, reducing contact resistance by approximately half and achieving higher two-dimensional electron gas concentrations, thereby enhancing the overall performance and reliability of the semiconductor device.
Implementation Method 1
high-concentration two-dimensional electron gas (2DEG) is generated at a lamination interface (hetero interface) owing to a polarization effect (spontaneous polarization effect and piezo polarization effect) inherent in a nitride material
Implementation Method 2
the most basic configuration of a substrate for HEMT device using a base substrate formed of heterogeneous single crystal is obtained by epitaxially forming a barrier layer, a channel layer and a buffer layer on a base substrate
Data Source
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AI summary
Provided is an epitaxial substrate capable of achieving a semiconductor device that has excellent ohmic contact characteristics as well as satisfactory device characteristics. On a base substrate, a channel layer formed of a first group III nitride that contains at least Al and Ga and has a composition of Inx1Aly1Gaz1N (x1+y1+z1=1) is formed. On the channel layer, a barrier layer formed of a second group III nitride that contains at least In and Al and has a composition of Inx2Aly2Gaz2N (x2+y2+z2=1) is formed such that an In composition ratio of a near-surface portion is larger than an In composition ratio of a portion other than the near-surface portion.