Semiconductor Layer Structure for Lower Recovery Loss
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Solution Overview
Problem
Semiconductor devices used for power conversion face challenges in reducing switching loss, particularly due to uncontrolled electron and hole current flows which lead to increased recovery loss during the transition from on-state to off-state.
Innovation Solution
The semiconductor device incorporates a specific layer structure with a fourth semiconductor layer of the first conductivity type embedded in the second semiconductor layer, which narrows the flow path of hole current and suppresses hole injection, thereby reducing recovery loss. This is achieved by positioning the fourth semiconductor layer between the third and second semiconductor layers, with insulating films separating these layers from the semiconductor part, and optimizing their spatial arrangement to control current paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional semiconductor layer structure is used, then the device structure is simple, but the switching loss increases due to uncontrolled electron and hole current flows
Solution Approach 1:
The semiconductor device is divided into multiple doped layers (first through fourth semiconductor layers) with different conductivity types and doping concentrations. This segmentation allows independent control of electron and hole current flows through each layer, enabling suppression of hole injection into the first semiconductor layer while maintaining low on-state voltage, thereby reducing switching loss without excessive complexity
Solution Approach 2:
Different regions of the semiconductor device are assigned different doping concentrations and conductivity types. The fourth semiconductor layer has higher doping concentration than the second layer, creating localized high-field regions that control carrier injection. This local quality variation enables precise control of current paths to reduce switching loss while keeping the overall structure manageable
2Loss of energy
If the fourth semiconductor layer is positioned closer to the first semiconductor layer, then hole injection is suppressed more effectively, but the risk of electrical breakdown between layers increases
Solution Approach 1:
The third semiconductor layer acts as an intermediary between the fourth semiconductor layer (high doping) and the first semiconductor layer. This intermediate layer with moderate doping concentration buffers the electric field, preventing direct high-field contact between the highly doped fourth layer and the first layer, thus suppressing hole injection while avoiding electrical breakdown
Solution Approach 2:
The doping concentration is gradually changed across the layers: the fourth layer has high doping, the third layer has moderate doping, and the first layer has lower doping. This parameter gradient smoothly transitions the electric field strength, enabling effective hole injection suppression while maintaining electrical breakdown resistance through controlled field distribution
Data Source
AI summary
A semiconductor device includes a semiconductor part, first to fourth electrodes, and first and second insulating film. The first and second electrodes are provided on back and front surfaces of the semiconductor part, respectively. The third and fourth electrodes each extend into the semiconductor device form the front surface side. The third and fourth electrodes are electrically insulated from the semiconductor part by insulating films. The semiconductor part includes first to fourth layers. The first layer of a first conductivity type extends between the first and second electrodes. The second layer of a second conductivity type is provided between the first layer and the second electrode. The third layer of the second conductivity type is partially provided between the second layer and the second electrode. The fourth layer of the first conductivity type is provided in the second layer. The fourth layer is apart from the third layer.