Pulsed Selective Area Lateral Epitaxy for III-Nitride Growth
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Solution Overview
Problem
The growth of high-quality, low-defect density non-polar and semi-polar III-Nitride films is hindered by high defect densities and lattice mismatch issues when deposited on substrates like sapphire, leading to inefficient optoelectronic devices due to piezoelectric polarization and threading dislocations.
Innovation Solution
A method involving pulsed selective area lateral overgrowth (P-SALE) using pulsed metal organic chemical vapor deposition (P-MOCVD) and pulsed atomic layer epitaxy (PALE) to grow non-polar or semi-polar group III nitride layers, where a base layer is masked with dielectric layers to allow controlled lateral growth, reducing dislocation propagation and enhancing crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-polar III-Nitride layers are deposited on sapphire substrates using conventional MOCVD or HVPE techniques, then the growth process is simple and straightforward, but threading dislocation density and stacking fault density are high (on the order of 1×10^9 cm^-2 and 5×10^5 cm^-2 respectively)
Solution Approach 1:
The growth process is segmented into multiple stages: initial layer growth, lateral overgrowth phase, and final non-polar layer deposition. The lateral overgrowth phase is further divided into pulsed sequences where precursor sources are supplied alternately. This segmentation allows control over defect propagation by limiting vertical growth during lateral expansion phases.
Solution Approach 2:
The patent employs periodic pulsing of precursor sources (group III metal source and nitrogen source) during the lateral overgrowth phase. The group III source is pulsed for a first time period, then the nitrogen source is pulsed for a second time period, creating a periodic deposition pattern that promotes lateral growth while suppressing vertical dislocation propagation and reduces stacking fault formation.
2Productivity
If continuous precursor supply is used in conventional MOCVD, then the growth rate is high and productivity is improved, but adduct formation increases leading to more stacking faults and higher dislocation density
Solution Approach 1:
The continuous precursor supply is replaced with periodic pulsing. The group III metal source is supplied during a first time period, then interrupted while the nitrogen source is supplied during a second time period. This periodic action prevents adduct formation by ensuring precursors are not present simultaneously, thereby reducing stacking faults while maintaining acceptable growth rates through optimized pulse durations.
Solution Approach 2:
The group III metal source is supplied in advance during the first time period before the nitrogen source is introduced. This preliminary action allows the metal source to be adsorbed and activated on the substrate surface, creating ready sites for nitrogen incorporation without the presence of nitrogen during metal source supply, thus preventing harmful adduct formation.
3Manufacturing precision
If lateral overgrowth is performed to reduce dislocation density, then threading dislocation density decreases, but the process complexity increases with additional masking and growth steps
Solution Approach 1:
The lateral overgrowth process is segmented into controlled phases using temporal pulsing rather than requiring complex spatial masking patterns. By dividing the deposition into sequential precursor supply periods, the method achieves lateral growth direction control and dislocation suppression without needing multiple masking layers and complex alignment steps, reducing overall process complexity.
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 significantly reduces threading dislocation and basal stacking fault densities, resulting in high-quality non-polar and semi-polar III-Nitride layers with improved device performance and efficiency, particularly for optoelectronic devices like LEDs and HEMTs.
Implementation Method 1
A nonpolar or semi-polar group III nitride layer is then grown from each side edge of the mushroom-shaped PLOG group III nitride layer by pulsing a nitrogen source and a group III metal source
Implementation Method 2
Group III-nitride and its ternary and quaternary compounds are prime candidates for fabrication of visible and ultraviolet high-power and high-performance optoelectronic devices and electronic devices. These devices are typically grown epitaxially as thin films
Data Source
AI summary
An epitaxy procedure for growing extremely low defect density non-polar and semi-polar III-nitride layers over a base layer, and the resulting structures, is generally described. In particular, a pulsed selective area lateral overgrowth of a group III nitride layer can be achieved on a non-polar and semi-polar base layer. By utilizing the novel P-MOCVD or PALE and lateral over growth over selected area, very high lateral growth conditions can be achieved at relatively lower growth temperature which does not affect the III-N surfaces.