GaN Semiconductor Light-Emitting Device Vertical Current Path
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Solution Overview
Problem
GaN-based semiconductor light-emitting devices fabricated on sapphire substrates face issues such as reduced light-emitting area due to electrode formation, high current density leading to heat generation, and poor thermal conductivity, along with challenges in bonding conductive substrates due to thermal expansion coefficient differences and resistance increases at the bonding interface.
Innovation Solution
A method involving a stacked body of n-type, light-emitting, and p-type semiconductor layers with metal bonding layers of identical crystal structure and orientation, and optionally a lattice-matching layer, bonded to a conductive substrate like silicon, with the substrate removed, and electrodes placed on either side to enhance bonding strength and reduce interface resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire single crystal substrate is used to form GaN-based semiconductor layers, then good nitride semiconductor formation is achieved through buffer layer, but the substrate being an insulator causes current flow in horizontal direction leading to heat generation
Solution Approach 1:
The patent inverts the conventional electrode configuration by placing the positive electrode on the sapphire substrate side and the negative electrode on the light-emitting layer side. This inversion changes the current flow direction from horizontal to vertical, passing through the light-emitting layer, thereby eliminating localized heat generation while maintaining good nitride semiconductor formation quality
Solution Approach 2:
The patent transitions the current flow from a two-dimensional horizontal path on the substrate surface to a three-dimensional vertical path through the stacked layers. This dimensional change allows current to pass through the light-emitting layer vertically, distributing heat more effectively and preventing localized overheating
2Device complexity
If both positive and negative electrodes are formed on the same surface side of the substrate, then electrode connection is simplified, but high current density is formed locally causing heat generation
Solution Approach 1:
The patent inverts the conventional same-side electrode configuration by placing electrodes on opposite sides of the stacked body. The positive electrode is formed on the sapphire substrate side while the negative electrode is formed on the light-emitting layer side, transforming current flow from horizontal to vertical and eliminating localized high current density
3Reliability
If the sapphire single crystal substrate is used, then insulator properties allow electrode formation, but low thermal conductivity prevents heat diffusion and increases device temperature
Solution Approach 1:
The patent extracts and removes the sapphire single crystal substrate after the stacked body is formed and electrodes are connected. This extraction eliminates the substrate's poor thermal conductivity limitation while preserving its role during fabrication, allowing the device to operate without the thermal management constraints of the insulating substrate
4Temperature
If bonding method is used to attach conductive substrate, then thermal management is improved, but fluctuation of thermal expansion coefficient and increased bonding interface resistance occur
Solution Approach 1:
The patent completely removes the sapphire substrate after forming the stacked body and connecting electrodes, eliminating the need for bonding to conductive substrates. This extraction approach avoids all bonding-related issues including thermal expansion coefficient mismatch and interface resistance, while thermal management is achieved through the vertical current flow path and subsequent substrate removal
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 approach strengthens the bonding between the semiconductor layers, reduces interface resistance, and improves thermal management, leading to enhanced performance and reliability of GaN-based semiconductor light-emitting devices.
Implementation Method 1
a second bonding layer formed on the electroconductive substrate, adapted to have bonded to the first bonding layer a bonding surface thereof lying opposite a side on which the electroconductive substrate is formed, made of a metal of a same crystal structure as the first bonding layer, and allowed to exhibit an identical crystal orientation in both a perpendicular direction of the bonding surface and an in-plane direction of the bonding surface
Data Source
Figure 1(A)~1(C)
Figure 2~3(B)
Figure 4~5(B)
AI summary
A GaN-based semiconductor light-emitting device 1 includes a stacked body 1OA having the component layers 12 that include an n-type semiconductor layer, a light- emitting layer and a p-type semiconductor layer each formed of a GaN-based semiconductor, sequentially stacked and provided as an uppermost layer with a first bonding layer 14 made of metal and a second bonding layer 33 formed on an electroconductive substrate 31, adapted to have bonded to the first bonding layer 14 the surface thereof lying opposite the side on which the electroconductive substrate 31 is formed, made of a metal of the same crystal structure as the first bonding layer 14, and allowed to exhibit an identical crystal orientation in the perpendicular direction of the bonding surface and the in-plane direction of the bonding surface.