Nanoporous GaN Blocking Layer for Mg Diffusion
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Solution Overview
Problem
Mg out-diffusion in GaN thin film growth using MOCVD leads to unreliable doping structures and device performance due to Mg incorporation into subsequent layers, blurring doping boundaries and reducing reliability.
Innovation Solution
Introduction of a nanoporous GaN (NP GaN) layer as a blocking layer to compensate for Mg out-diffusion, providing an ex-situ-formed interface with oxygen and carbon impurities to mitigate Mg diffusion and enhance the embedding of p-type gallium nitride in multi-junction structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MOCVD is used for thin film growth on p-GaN, then manufacturing efficiency is improved, but Mg out-diffusion occurs causing unreliable doping structures
Solution Approach 1:
A nanoporous GaN (NP-GaN) interlayer is introduced between the p-GaN layer and the subsequent thin film layers. This intermediary layer acts as a diffusion barrier that prevents Mg atoms from migrating into the adjacent layers, thereby maintaining doping structure reliability while allowing MOCVD processing to continue.
Solution Approach 2:
The NP-GaN layer is formed with a nanoporous structure through electrochemical etching. This porous structure provides a large surface area and acts as an effective barrier to Mg diffusion while maintaining structural integrity and compatibility with the MOCVD growth process.
2Quantity of substance
If Mg doping is applied to GaN, then p-type conductivity is achieved, but Mg atoms remain on surface and in reactor causing out-diffusion
Solution Approach 1:
The NP-GaN layer serves as a mediator that captures and retains Mg atoms that would otherwise diffuse into subsequent layers. The porous structure provides sites for Mg accumulation, preventing the harmful out-diffusion while preserving the p-type conductivity of the underlying p-GaN layer.
Solution Approach 2:
The NP-GaN layer converts the harmful effect of Mg out-diffusion into a beneficial barrier function. The Mg atoms that would contaminate subsequent layers are instead trapped in the nanoporous structure, transforming the diffusion problem into an effective blocking mechanism.
3Reliability
If NP GaN is introduced as blocking layer, then Mg out-diffusion is compensated, but additional layer adds to structure complexity
Solution Approach 1:
The NP-GaN layer is formed by modifying the electrical parameters of an existing GaN layer through electrochemical etching, rather than introducing a completely new material. This parameter-based transformation maintains material compatibility while adding the necessary blocking function with minimal additional complexity.
Solution Approach 2:
The structure combines the p-GaN layer with the NP-GaN interlayer to create a composite structure that leverages the complementary properties of each component: the p-type conductivity of GaN and the diffusion-blocking capability of the nanoporous structure.
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
NP GaN effectively compensates for Mg out-diffusion, maintaining high crystalline quality and electron concentration in 2DEG structures, enabling reliable bandgap engineering and performance in III-nitride-based devices, such as CAVETs and super junction devices.
Implementation Method 1
NP GaN on p-GaN provides an ex-situ-formed interface with oxygen and carbon impurities, compensating Mg out-diffusion from p-GaN
Implementation Method 2
NP GaN on p-GaN provides an ex-situ-formed interface with oxygen and carbon impurities, compensating Mg out-diffusion from p-GaN
Data Source
AI summary
Improved fabrication is provided for devices in the GaN material system that require an embedded p-type layer. The effect of Mg diffusion from the p-type layer is compensated for using an GaN interlayer that is etched to be nanoporous at its top surface. In addition to serving as a diffusion barrier, the GaN interlayer preferably has C and O impurities from the etch that tend to compensate unwanted Mg doping in layers above the GaN interlayer. Importantly, the entire structure can be grown at high temperatures, which desirably avoids low temperature growth steps that tend to reduce material quality.