HEMT Doping Profile to Limit Channel Sheet Resistance Drift
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Solution Overview
Problem
The challenge in high electron mobility transistors (HEMTs) is to reduce the influence of dopants on the sheet resistance value of the channel layer, as dopants in the buffer layer can diffuse and increase the sheet resistance, affecting the device's performance.
Innovation Solution
The HEMT structure includes a substrate, nucleation layer, buffer layer, and channel layer, where the channel layer has a dopant doping concentration less than the buffer layer, with a dopant concentration at the interface between the channel and barrier layers equal to or greater than 1×10^15 cm^-3, formed using metal organic chemical vapor deposition (MOCVD), and the dopant concentration in the buffer layer is greater than or equal to 2×10^17 cm^-3, with a specific distribution and decrease towards the channel layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping is performed on the buffer layer to improve HEMT performance, then the device performance is improved, but the dopant diffuses to the channel layer and increases the sheet resistance value
Solution Approach 1:
The patent applies local quality by creating a graded doping concentration profile in the buffer layer, where the dopant concentration varies spatially - higher near the substrate and lower near the channel layer interface. This localized variation in doping concentration allows the buffer layer to provide necessary electrical properties while minimizing dopant diffusion harm to the channel layer.
Solution Approach 2:
The patent changes the doping concentration parameter across the buffer layer thickness, transitioning from a uniform high concentration to a graded profile. Specifically, the dopant concentration is reduced near the channel layer interface to equal or less than 1×10^18 atoms/cm³, which significantly reduces the harmful diffusion effect while maintaining the buffer layer's functional properties.
2Reliability
If the dopant concentration in the buffer layer is increased to improve performance, then the HEMT performance improves, but the sheet resistance value of the channel layer increases due to dopant diffusion
Solution Approach 1:
The patent implements local quality by establishing different dopant concentration levels in different regions of the buffer layer. The region adjacent to the channel layer has a specifically controlled low dopant concentration (≤1×10^18 atoms/cm³), while other regions can have higher concentrations, thus locally optimizing both performance and sheet resistance characteristics.
Solution Approach 2:
The patent applies preliminary action by pre-establishing a graded doping profile in the buffer layer before the channel layer is formed. This preliminary concentration gradient prevents excessive dopant diffusion into the channel layer during subsequent processing, thereby pre-controlling the sheet resistance value to remain within the desired range (50-200 Ω/□).
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 design reduces the impact of metal dopants on the sheet resistance of the nitride channel layer, resulting in improved HEMT performance with optimized thickness and doping concentration, enhancing the transistor's characteristics.
Implementation Method 1
a dopant in the buffer layer would diffuse to a channel layer
Implementation Method 2
formed using metal organic chemical vapor deposition (MOCVD)
Data Source
AI summary
An improved high electron mobility transistor (HEMT) structure includes in order a substrate, a nucleation layer, a buffer layer, a channel layer, and a barrier layer, wherein the buffer layer includes a dopant. The channel layer having a dopant doping concentration less than that of the buffer layer. A two-dimension electron gas is formed in the channel layer along an interface between the channel layer and the barrier layer. A dopant doping concentration of the channel layer at an interface between the channel layer and the barrier layer is equal to or greater than 1×1015 cm−3.