Nitride Semiconductor Hole Transport Layer Design
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Solution Overview
Problem
Current nitride semiconductor light emitting devices face limitations in improving hole injection efficiency and internal quantum efficiency due to challenges in preventing electron overflow and enhancing hole mobility.
Innovation Solution
A light emitting device structure is developed with a p-type semiconductor layer comprising a hole injection layer, a hole transport layer with undoped and doped layers, and a p-type contact layer, where the hole transport layer includes undoped layers with decreasing hole concentration and an intermediate doped layer to enhance hole mobility, and a method of fabricating this structure using metal organic chemical vapor deposition with specific gas flow ratios and temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an electron blocking layer is adopted to prevent electron overflow, then luminous efficacy is improved, but hole injection efficiency remains limited
Solution Approach 1:
The p-type semiconductor layer is segmented into multiple functional layers: a hole injection layer adjacent to the electron blocking layer, a hole transport layer in the middle, and a p-type contact layer at the bottom. This segmentation allows each layer to be optimized for its specific function, with the hole injection layer focusing on injecting holes into the active layer while the electron blocking layer prevents electron overflow, thereby resolving the contradiction between improving luminous efficacy and maintaining hole injection efficiency.
Solution Approach 2:
Different regions of the p-type semiconductor layer are given different dopant concentrations and material compositions tailored to their specific functions. The hole injection layer has optimized dopant concentration to facilitate hole injection, the hole transport layer has properties optimized for hole transport, and the p-type contact layer has properties optimized for electrical contact. This local optimization allows simultaneous achievement of high luminous efficacy through electron blocking and high hole injection efficiency.
2Reliability
If dopant concentration is increased to improve hole injection, then hole injection efficiency improves, but hole mobility decreases
Solution Approach 1:
The p-type semiconductor layer is divided into multiple layers with different dopant concentrations. The hole injection layer has higher dopant concentration to ensure efficient hole injection into the active layer, while the hole transport layer has lower dopant concentration to maintain high hole mobility for effective hole transport. This segmentation resolves the contradiction by allowing high dopant concentration where needed for injection while maintaining low dopant concentration where mobility is critical for transport.
Solution Approach 2:
Each layer within the p-type semiconductor structure is given locally optimized dopant concentration and material composition. The hole injection layer receives higher dopant concentration specifically at the interface with the active layer to maximize hole injection efficiency, while the bulk of the hole transport layer maintains lower dopant concentration to preserve hole mobility. This local quality optimization enables simultaneous achievement of high hole injection efficiency and high hole mobility in their respective functional regions.
3Speed
If undoped layers are used to increase hole mobility, then hole mobility increases, but electrostatic discharge withstand voltage decreases
Solution Approach 1:
The p-type semiconductor layer is segmented into doped and undoped regions, with undoped layers positioned in the hole transport region to maximize hole mobility, and doped layers positioned at the contact region to provide electrostatic discharge protection. This spatial segmentation allows the undoped layers to enhance hole mobility where needed while the doped layers provide electrostatic discharge withstand voltage where required, resolving the contradiction between these two requirements.
Solution Approach 2:
Different regions of the p-type semiconductor layer are given different dopant concentrations based on their specific functional requirements. The hole transport layer is made undoped or lightly doped to maximize hole mobility for efficient hole transport to the active layer, while the p-type contact layer is heavily doped to provide low resistance electrical contact and electrostatic discharge protection. This local quality differentiation resolves the contradiction by applying the appropriate dopant concentration in each region to satisfy its specific functional requirements.
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 configuration improves hole injection efficiency, increases internal quantum efficiency, and enhances electrostatic discharge withstand voltage by increasing hole mobility and reducing dopant concentration in the undoped layers, resulting in higher luminous efficacy and lower forward voltages.
Implementation Method 1
growing a hole injection layer on the substrate within the chamber by introducing an N source gas, a Ga source gas, an Mg source gas, N2 gas, and H2 gas into the chamber
Data Source
AI summary
A light emitting device is provided to include an n-type semiconductor layer, a p-type semiconductor layer, an active layer, and an electron blocking layer disposed between the p-type semiconductor layer and the active layer. The p-type semiconductor layer includes a hole injection layer, a p-type contact layer, and a hole transport layer. The hole transport layer includes a plurality of undoped layers and at least one intermediate doped layer disposed between the undoped layers. At least one of the undoped layers includes a zone in which hole concentration decreases with increasing distance from the hole injection layer or the p-type contact layer, and the intermediate doped layer is disposed to be at least partially overlapped with a region of the hole transport layer, the region having the hole concentration of 62% to 87% of the hole concentration of the p-type contact layer.