Single Crystalline AlN Substrates for Deep-UV LED Defect Reduction
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Solution Overview
Problem
Commercially available ultraviolet (UV) optoelectronic devices, particularly deep-UV LEDs, suffer from short lifetimes and low light emission efficiency due to high dislocation densities resulting from substrate incompatibility, limiting their performance and reliability.
Innovation Solution
Fabrication of UV light-emitting devices on high-quality single crystalline aluminum nitride (AlN) substrates with low dislocation density using physical vapor transport (PVT) to reduce defect density and improve lattice matching, resulting in devices with significantly lower reverse leakage current and extended operational lifetimes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If sapphire substrates are used to fabricate III-nitride based UV devices, then low-cost devices can be obtained due to high transparency, but device lifetime is very low due to high dislocation density
Solution Approach 1:
The patent changes the substrate material parameter from sapphire to single crystalline AlN, which has a lattice constant much closer to III-nitride semiconductor layers. This parameter change reduces lattice mismatch from approximately 13-17% with sapphire to less than 3% with AlN, thereby reducing dislocation density from 10^9-10^10 cm^-2 to below 10^6 cm^-2 and extending device lifetime from tens of hours to over 10,000 hours.
Solution Approach 2:
The patent employs a composite structure consisting of a single crystalline AlN substrate combined with III-nitride semiconductor layers (GaN, AlGaN). This composite material system leverages the high transparency and low defect density of AlN to support the light-emitting III-nitride layers, achieving both high efficiency and long lifetime in UV device operation.
2Ease of manufacture
If sapphire substrates are used for UV device fabrication, then manufacturing cost is reduced, but device reliability deteriorates due to substrate-device layer incompatibility
Solution Approach 1:
The patent changes the substrate material parameter from sapphire to single crystalline AlN, which has a lattice constant much closer to III-nitride semiconductor layers. This parameter change reduces lattice mismatch from approximately 13-17% with sapphire to less than 3% with AlN, thereby reducing dislocation density from 10^9-10^10 cm^-2 to below 10^6 cm^-2 and extending device lifetime from tens of hours to over 10,000 hours.
3Reliability
If UV LEDs are designed with excessive output power at beginning of life to compensate for short lifetime, then system design complexity increases, but this does not extend actual device lifetime
Solution Approach 1:
The patent takes preliminary action by using single crystalline AlN substrates with dislocation density below 10^6 cm^-2 to fabricate UV LEDs that inherently achieve over 10,000 hours of lifetime. This preliminary improvement in substrate quality eliminates the need for subsequent system design compensations, allowing devices to operate at rated power without excessive output power margins while maintaining simple system design.
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 use of low-dislocation-density AlN substrates leads to UV devices with enhanced electrical efficiency, increased internal quantum efficiency, and remarkably long lifetimes, with L80 output power exceeding 2000 hours at specific current densities, compared to traditional sapphire-substrate devices.
Implementation Method 1
The ability to provide UV-emitting devices featuring stable light output and long lifetimes would simplify system design and lower costs. However, commercially available devices operating in the UV range, particularly in the deep-UV range, have not reached the level of efficiency and technological maturity of the visible light-emitting devices.
Implementation Method 2
Fabrication of UV light-emitting devices on high-quality single crystalline aluminum nitride (AlN) substrates with low dislocation density using physical vapor transport (PVT) to reduce defect density and improve lattice matching
Implementation Method 3
Optoelectronic devices, for example semiconductor light sources, are devices in which an optical input produces an electrical output, or in which electrical stimulation produces visible, infrared or ultraviolet output.
Data Source
AI summary
The invention provides an optoelectronic device adapted to emit ultraviolet light, including an aluminum nitride single crystalline substrate, wherein the dislocation density of the substrate is less than about 105 cm−2 and the Full Width Half Maximum (FWHM) of the double axis rocking curve for the (002) and (102) crystallographic planes is less than about 200 arcsec; and an ultraviolet light-emitting diode structure overlying the aluminum nitride single crystalline substrate, the diode structure including a first electrode electrically connected to an n-type semiconductor layer and a second electrode electrically connected to a p-type semiconductor layer. In certain embodiments, the optoelectronic devices of the invention exhibit a reverse leakage current less than about 10−5 A/cm2 at −10 V and/or an L80 of at least about 5000 hours at an injection current density of 28 A/cm2.