Non-polar UV LED Using Pulsed Lateral Overgrowth to Reduce Defects
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Solution Overview
Problem
The manufacturing of ultraviolet light-emitting diodes (UV LEDs) is hindered by defects such as lattice and thermal mismatch, impurities, and crystalline defects in Group III-nitride semiconductor layers, leading to reduced efficiency and lifetime, particularly for aluminum-containing materials, and conventional deposition techniques fail to produce high-quality deep UV LEDs.
Innovation Solution
A non-polar ultraviolet light-emitting device is fabricated using a template with a non-c-plane substrate and pulsed lateral overgrowth (PLOG) techniques, involving multiple III-Nitride buffer layers and superlattices, which reduces defect density and strain, and incorporates pulsed atomic layer epitaxy (PALE) for improved layer quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional deposition techniques are used to grow III-nitride layers on c-plane substrates, then the manufacturing process is simple, but the defect density is high and device lifetime is reduced
Solution Approach 1:
The manufacturing process is segmented into multiple stages: initial buffer layer growth on c-plane substrate, selective area growth to form patterned regions, and subsequent lateral overgrowth. This segmentation allows defect filtering at each stage while maintaining overall process feasibility.
Solution Approach 2:
A buffer layer is grown preliminarily on the c-plane substrate before the main device layers. This preliminary layer serves to filter dislocations and reduce defect density before subsequent critical layers are deposited, improving device reliability without requiring complete process redesign.
2Illumination intensity
If aluminum-containing III-Nitride materials are used for deep UV emission, then the UV emission performance is improved, but aluminum sticks to masked material and disrupts lateral overgrowth
Solution Approach 1:
An aluminum gallium nitride (AlGaN) intermediate layer is introduced between the aluminum nitride buffer and the subsequent layers. This intermediary layer has reduced aluminum content and different growth characteristics that prevent aluminum sticking to masked regions, enabling successful lateral overgrowth while maintaining deep UV emission capability.
Solution Approach 2:
The aluminum composition parameter is varied through the layer structure - high aluminum content in the buffer for defect filtering, then reduced aluminum content in intermediate and active layers for controlled lateral growth. This parameter modulation resolves the contradiction between UV performance and growth quality.
3Reliability
If c-plane substrate is used for III-nitride growth, then the substrate availability is high, but threading dislocation density is high and radiative efficiency is reduced
Solution Approach 1:
The device structure is designed with regions of different quality: the buffer layer region handles dislocation filtering, while the active region maintains high crystal quality for radiative efficiency. This local quality differentiation allows use of readily available c-plane substrates while achieving high radiative efficiency in the emission region.
Solution Approach 2:
The approach transitions from two-dimensional planar growth to three-dimensional lateral overgrowth. By growing layers laterally from patterned regions rather than uniformly across the surface, dislocations are excluded from the active regions, improving radiative efficiency while maintaining compatibility with standard c-plane substrates.
4Manufacturing precision
If standard MOCVD or MBE techniques are used for AlInGaN growth, then the deposition process is straightforward, but gas phase reaction of precursor sources reduces epilayer quality
Solution Approach 1:
The deposition process uses periodic pulsing of precursor sources rather than continuous flow. This pulsed delivery method prevents gas phase reactions by ensuring precursors are introduced sequentially in time and space, improving epilayer quality while using standard MOCVD equipment.
Solution Approach 2:
The lateral overgrowth process maintains continuous material supply to the growing fronts without interruption. This continuous action ensures uniform composition and structure in the critical active regions, compensating for the increased process complexity through sustained controlled growth.
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 approach results in reduced defect density and enhanced radiative efficiency, enabling the production of high-quality, reliable deep UV LEDs with improved performance and extended lifetime.
Implementation Method 1
a low defect density III-Nitride second buffer layer is formed thereover by using a pulsed lateral overgrown III-Nitride layer
Implementation Method 2
the use of pulsed atomic layer epitaxy (PALE) to improve the quality of the buffer AlN layer; the use of a PALE deposited AlN/AlxGa1-xN, short-period super-lattice layer insertion
Data Source
AI summary
An ultra-violet light-emitting device and method for fabricating an ultraviolet light emitting device, 12, (LED or an LD) with an AlInGaN multiple-quantum-well active region, 10, exhibiting stable cw-powers. The device includes a non c-plane template with an ultraviolet light-emitting structure thereon. The template includes a first buffer layer, 321, on a substrate, 100, then a second buffer layer, 421, on the first preferably with a strain-relieving layer, 302, in both buffer layers. Next there is a semiconductor layer having a first type of conductivity, 500, followed by a layer providing a quantum-well region, 600. Another semiconductor layer, 700, having a second type of conductivity is applied next. Two metal contacts, 980 and 990, are applied to this construction, one to the semiconductor layer having the first type of conductivity and the other to the semiconductor layer having the second type of conductivity, to complete the light emitting device.