Composite metal substrate for thin film AlGaInP LED applications

Current LED technologies face challenges in heat dissipation and thermal stability. Traditional substrates like GaAs have limitations in thermal conductivity, which affects performance under high current. While copper substrates offer better thermal properties, their coefficient of thermal expansion does not match LED materials, leading to strain and performance degradation. Prior research has shown that mismatched thermal expansion causes red shifts in emitted wavelengths. No prior work had resolved the balance between high thermal conductivity and thermal expansion compatibility in LED substrates. This gap motivated the exploration of composite metal substrates. The need for a material that matches both thermal and mechanical properties of LED layers remained unmet. Researchers sought a solution that could maintain optical performance while improving thermal management. The challenge was to integrate a substrate that supports high current operation without significant wavelength shifts. The goal was to develop a structure that could be applied to conventional vertical LED designs.

The aim of this study was to evaluate a copper-invar-copper composite (CIC) substrate for use in thin-film AlGaInP LEDs. The researchers focused on addressing the mismatch between thermal expansion coefficients of traditional substrates and LED materials. They sought to develop a structure that could maintain optical stability under high current. The motivation was to improve LED performance by reducing thermal-induced wavelength shifts. The study aimed to demonstrate that a composite metal substrate could offer both thermal conductivity and mechanical compatibility. The researchers also wanted to assess the feasibility of using this substrate in conventional vertical LED designs. They hypothesized that the CIC structure would allow for better heat dissipation without compromising optical output. The study's success would provide a scalable solution for high-efficiency LED manufacturing.

The researchers used wafer bonding and epilayer transferring technologies to fabricate the LEDs. The CIC substrate was composed of three layers: a 20 μm top copper layer, a 64 μm middle invar layer, and a 20 μm bottom copper layer. The invar layer contained 70% iron and 30% nickel. The thermal expansion coefficient of the CIC was measured at 6.1 × 10^-6 /K. This value was compared to GaAs and AlGaInP materials to assess compatibility. LEDs were fabricated with an emitting area of 1 mm × 1 mm. The thermal conductivity of the CIC was measured at 160 W/m-K. The performance of the LEDs was evaluated under varying current loads.

The CIC substrate enabled LEDs with a low red shift of 19 nm when current increased from 100 mA to 1 A. The output power reached 212 mW at 800 mA. The thermal expansion coefficient of the CIC matched that of GaAs and AlGaInP. This alignment reduced mechanical strain in the LED structure. The thermal conductivity of the CIC was significantly higher than traditional substrates. This property allowed for efficient heat dissipation during operation. The LEDs demonstrated stable optical performance under high current. The study confirmed the feasibility of using the CIC substrate in vertical LED designs.

The study demonstrated that the CIC substrate is compatible with AlGaInP LEDs in terms of thermal expansion. The researchers propose that this compatibility reduces strain and improves optical stability. The high thermal conductivity of the CIC allows for efficient heat dissipation. This property supports high current operation without significant wavelength shifts. The LEDs fabricated with the CIC substrate showed a red shift of only 19 nm. The output power at 800 mA reached 212 mW. The authors suggest that the CIC structure can be extended to conventional vertical LED designs. The findings support the use of composite metal substrates in LED manufacturing.