Thin N-GaN Light Emitting Device with Transparent Conductive Oxide
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Solution Overview
Problem
III-nitride light emitting devices grown on non-native substrates face strain issues due to lattice and thermal mismatches, leading to reduced output and increased costs, as thick n-type regions are required for current spreading, which can result in cracking and inefficiency.
Innovation Solution
A semiconductor structure with a thin n-type region and a transparent, conductive non-III-nitride material in direct contact, reducing the need for thick n-type regions and alleviating strain by using a transparent conductive oxide to spread current, thereby minimizing light absorption and maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick n-type region is used for current spreading, then electrical conductivity is improved, but strain and cracking increase
Solution Approach 1:
A transparent conductive oxide layer is introduced as an intermediary between the n-type GaN layer and the electrode. This TCO layer has high electrical conductivity and serves as the primary current spreading path, allowing the n-type GaN layer to be much thinner without compromising electrical performance. The thinner GaN layer experiences reduced strain, eliminating cracking while maintaining low sheet resistance through the TCO intermediary.
2Strength
If the n-type region thickness is reduced, then strain and cracking are reduced, but current spreading capability deteriorates
Solution Approach 1:
The transparent conductive oxide acts as a mediator that takes over the current spreading function from the n-type GaN layer. By depositing the TCO layer (such as ITO, ZnO, or SnO2) with appropriate thickness and doping, high electrical conductivity is achieved, enabling effective current distribution even when the underlying GaN layer is thin, thus decoupling current spreading capability from GaN layer thickness.
Solution Approach 2:
The electrical conductivity parameter of the contact structure is improved by introducing the TCO layer with high carrier concentration and mobility. This parameter change allows the system to achieve low sheet resistance through the TCO rather than relying on a thick GaN layer, thereby enabling thin GaN structures without sacrificing current spreading.
3Manufacturing precision
If a conventional GaN template is used, then lattice constant control is achieved, but compressive strain in the light emitting layer increases
Solution Approach 1:
The transparent conductive oxide layer serves as an intermediary between the electrode and the thin n-type GaN layer, allowing the GaN layer to be grown with optimized thickness and composition. The TCO layer compensates for any lattice mismatch effects and provides a compliant substrate that reduces compressive strain accumulation in the light emitting layer while maintaining precise lattice constant control through the GaN template.
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 solution allows for a thinner n-type region, reducing strain and cracking, while maintaining low sheet resistance and efficient light emission, thus enhancing device performance and reducing production costs.
Implementation Method 1
A transparent, conductive non-III-nitride material is disposed in direct contact with the n-type region
Implementation Method 2
Growth of thick layers can reduce the output of the device, and require extra source material, which can increase the cost of a device. If the device layers are grown overly thick, the strain may be relieved by cracking
Data Source
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AI summary
A device includes a semiconductor structure comprising a Ill-nitride light emitting layer disposed between an n-type region and a p-type region. A transparent, conductive non-III-nitride material is disposed in direct contact with the n-type region. A total thickness of semiconductor material between the light emitting layer and the transparent, conductive non-III-nitride material is less than one micron.