研究目的
To propose an Ag reflector layer with an AgCu alloy layer as a thermally reliable reflector for high power flip-chip and vertical light emitting diodes (LEDs), achieving enhanced reflectance and lower contact resistance after annealing.
研究成果
The alloyed AgCu/Ag reflector annealed at 500°C achieved a high reflectance of 78% and low contact resistance of 7.0 × 10^{-5} Ω·cm2, with LEDs showing lower forward-bias voltage and 23% higher light output power compared to as-deposited reflectors. This makes it a suitable thermally reliable reflector for high-efficiency flip-chip or vertical LEDs.
研究不足
The study is limited to specific Ag and Cu layer thicknesses and annealing conditions; higher temperatures (e.g., 600°C) led to increased void areas and degraded performance. The method may not be optimized for all LED structures or industrial scalability.
1：Experimental Design and Method Selection:
The study involved fabricating alloyed AgCu/Ag reflectors on GaN-based LEDs by depositing Ag and Cu layers using an e-beam evaporator and annealing them at various temperatures (300°C, 400°C, 500°C, 600°C) in ambient O2 to form AgCu alloys and CuO nano dots. The design aimed to suppress Ag agglomeration and improve optical and electrical properties.
2：Sample Selection and Data Sources:
LEDs composed of p-type GaN, InGaN MQWs, n-type GaN, and undoped GaN on sapphire substrates were used. Two sets with different Ag layer thicknesses (30 nm and 50 nm) were prepared, with a 1 nm Cu layer and a 150 nm Ag layer deposited on top.
3：List of Experimental Equipment and Materials:
Equipment included an e-beam evaporator for deposition, annealing furnace, scanning electron microscopy (SEM) for surface analysis, ultraviolet-visible (UV-Vis) spectrophotometer for reflectance measurements, parameter analyzer (KEITHLEY-2420 sourcemeter) for electrical characterization, and Newport 1930C powermeter for light output measurements. Materials included Ag, Cu, Ti, Al, GaN, InGaN, and sapphire substrates.
4：Experimental Procedures and Operational Workflow:
LEDs were etched to expose n-type GaN, n-electrodes (Ti/Al) were annealed at 550°C, Ag/Cu/Ag multilayers were deposited, samples were annealed at specified temperatures, and structural, optical, and electrical properties were analyzed using SEM, UV-Vis, I-V, and L-I measurements.
5：Data Analysis Methods:
Reflectance was calibrated using as-deposited Ag layers, contact resistance was measured using circular transmission-line model (CTLM) patterns, and data were analyzed to compare performance across annealing temperatures.
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