Alternating Stress Epitaxy for Semiconductor Layer Integrity
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Solution Overview
Problem
Existing methods for growing semiconductor layers, particularly for light emitting devices like LEDs, face challenges in minimizing dislocation density and cracks, which affect efficiency, as they struggle to achieve uniform composition and control stress in nitride-based semiconductor layers.
Innovation Solution
The approach involves alternating epitaxial growth periods with layers of tensile and compressive stress, using varying molar ratios of group V to group III precursors to achieve approximately zero overall residual stress, thereby reducing cracks and threading dislocations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick AlGaN epitaxial layers are grown to reduce current crowding, then device efficiency improves, but stress accumulation increases leading to cracks and dislocations
Solution Approach 1:
The patent divides the thick AlGaN layer into multiple thin sublayers separated by AlN spacer layers, creating a superlattice structure. This segmentation allows each thin layer to accommodate stress independently, preventing crack propagation through the entire thick layer while maintaining the required thickness for current spreading.
Solution Approach 2:
The patent varies the thickness parameters of AlGaN active layers and AlN spacer layers to control stress distribution. By adjusting these dimensional parameters, the structure achieves near-zero net stress while maintaining sufficient total AlGaN thickness for device performance.
2Reliability
If AlN buffer layers are used to reduce dislocation density, then threading dislocation density decreases, but composition uniformity becomes difficult to achieve
Solution Approach 1:
The patent employs continuous low-pressure metalorganic chemical vapor deposition (LP-MOCVD) to grow both AlN and AlGaN layers with uniform composition. This continuous growth process, as opposed to pulsed methods, ensures consistent stoichiometry and eliminates composition variations that arise from intermittent precursor delivery.
Solution Approach 2:
The patent optimizes deposition parameters including temperature, pressure, and precursor flow rates to achieve uniform AlN and AlGaN composition. Specific control of these parameters during LP-MOCVD ensures consistent layer stoichiometry while maintaining low dislocation densities.
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 method results in a semiconductor structure with reduced cracks and dislocations, enhancing the efficiency of semiconductor devices by effectively managing stress and composition uniformity.
Implementation Method 1
growing a plurality of semiconductor layers over a substrate using a set of epitaxial growth periods
Implementation Method 2
each epitaxial growth period includes: epitaxially growing a first semiconductor layer having one of: a tensile stress or a compressive stress; and epitaxially growing a second semiconductor layer having the other of: the tensile stress or the compressive stress directly on the first semiconductor layer
Data Source
AI summary
A solution for fabricating a semiconductor structure is provided. The semiconductor structure includes a plurality of semiconductor layers grown over a substrate using a set of epitaxial growth periods. During each epitaxial growth period, a first semiconductor layer having one of: a tensile stress or a compressive stress is grown followed by growth of a second semiconductor layer having the other of: the tensile stress or the compressive stress directly on the first semiconductor layer.