Nitride Semiconductor Buffer Layer Carbon Segmentation
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Solution Overview
Problem
Nitride semiconductor power devices face challenges with current collapse and leakage current, where controlling residual carbon concentration in the buffer layer to improve both properties simultaneously is difficult, and existing methods struggle to achieve high withstand voltage.
Innovation Solution
A nitride semiconductor substrate is developed with a buffer layer structure comprising a multilayer stack of Al or Ga nitride layers and a doping layer with controlled carbon and Si concentrations, along with an oxygen concentration, to reduce leakage current and control current collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If residual carbon concentration in the buffer layer is increased to reduce leakage current, then leakage current is reduced, but current collapse property deteriorates
Solution Approach 1:
The buffer layer is divided into multiple sub-layers with different carbon concentrations. The lower sub-layer has higher carbon concentration for leakage current reduction, while the upper sub-layer has lower carbon concentration for current collapse control. This segmentation allows simultaneous optimization of both properties that cannot be achieved with a uniform carbon concentration buffer layer.
Solution Approach 2:
Different regions of the buffer layer are assigned different carbon concentrations according to their functional requirements. The region closer to the GaN layer has lower carbon concentration to control current collapse, while regions farther away have higher carbon concentration to reduce leakage current. This local quality differentiation resolves the contradiction between the two opposing requirements.
2Reliability
If residual carbon concentration in the buffer layer is decreased to improve current collapse property, then current collapse property is improved, but leakage current increases
Solution Approach 1:
The buffer layer is segmented into multiple sub-layers where the upper sub-layer has lower carbon concentration to improve current collapse property, while the lower sub-layer maintains higher carbon concentration to suppress leakage current. This segmentation enables both properties to be optimized simultaneously without compromise.
Solution Approach 2:
The buffer layer exhibits spatial variation in carbon concentration, with lower concentration near the GaN interface for current collapse control and higher concentration in deeper regions for leakage current reduction. This local quality approach allows each region to fulfill its specific functional requirement.
3Object-generated harmful factors
If buffer layer is doped with carbon to achieve high resistance, then leakage current is reduced, but current collapse property deteriorates
Solution Approach 1:
The carbon-doped buffer layer is segmented into multiple sub-layers with progressively decreasing carbon concentrations. This gradient structure allows the buffer layer as a whole to maintain high resistance for leakage current reduction, while the lower-carbon regions near the GaN layer control current collapse property.
Solution Approach 2:
The carbon concentration parameter is varied spatially within the buffer layer, creating a gradient from high concentration at the substrate interface to low concentration at the GaN interface. This parameter change enables simultaneous achievement of high resistance for leakage reduction and low carbon concentration for current collapse control.
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 substrate effectively reduces leakage current and controls current collapse, enabling the use of nitride semiconductor substrates in high withstand voltage power devices.
Implementation Method 1
residual carbon compensates for residual donor in a GaN-type semiconductor crystal, and allows this crystal to have high resistance
Implementation Method 2
a multilayer stack in which a pair of nitride layers having different concentrations of Al or Ga are repeatedly deposited a plurality of times on an initial layer of AlxGa1−xN
Data Source
AI summary
A nitride semiconductor substrate suitable for a high withstand voltage power device is provided in which current collapse is controlled, while reducing leakage current. In a nitride semiconductor substrate, wherein a buffer layer, an active layer, and an electron supply layer, each comprising a group 13 nitride, are stacked one by one on a silicon single crystal substrate, the buffer layer has a structure where a multilayer stack in which a pair of nitride layers having different concentrations of Al or Ga are repeatedly deposited a plurality of times on an initial layer of AlxGa1−xN (0≦x≦1) is stacked, and includes a doping layer whose carbon concentration is 1×1018 to 1×1021 cm−3 and whose Si concentration is 1×1017 to 1×1020 cm−3, a thickness of the doping layer is 15% or more of the total thickness of the buffer layer.