Verticle, an LED chip maker in Silicon Valley with production in Korea, has come out with a hexagonally shaped UV-LED on a copper substrate that can be driven at high current. The chip employs what the company calls Chemical Chip Separation Technology between the Cu substrate and the GaN-based UV-LED. Verticle points out that despite their numerous advantages UV LEDs tend to have lower optical power due to lower internal quantum efficiency (IQE) compared to blue LEDs.

While improving the IQE of UV epitaxial wafers is a long-term prospect, Verticle contends that an alternative way to boost the overall output of a UV-LED is to drive more current into the UV-LEDs, and manage the resulting heat. The company states that heat-related droop is more of an issue in UV-LEDs than in blue, and therefore, the company reasons, one of the main challenges of UV LEDs is lowering junction temperature.

In order to operate at higher current injection conditions and dissipating heat more efficiently, Verticle’s UV-LED chip is constructed with a copper substrate. As shown in the accompanying image that contains both graphs, Cu base vertical chip’s thermal resistance (Rth) is 2K/W lower than GaN/Si vertical chip. As a result, junction temperature (Tj) of GaN/Cu is lower than GaN/Si. It is noted that the junction temperature difference is 2 degrees C at 350 mA current injection between two chips, however, the difference become larger (6 degrees C) at 1A current injection.

The company points to testing it conducted that shows that a vertical Cu-base UV-LED chip has higher radiant flux than a lateral chip fabricated with same epitaxial wafer. Furthermore, Verticle says that its UV-LED chip on a Cu substrate can be driven at a higher current than other vertical chips constructed with different substrate materials. For example, the company says that Verticle’s GaN/Cu UV-LED chip does not saturate over 1A, while GaN/sapphire UV-LED chip start to saturate after 500mA. This suggests that a GaN/Cu chip has higher heat dissipation capability compared with GaN on other substrates, giving Verticle’s Cu-base UV-LED chip distinct advantages for applications in which high current injection and good thermal properties are required.

Verticle’s hexagonal UV-LED chip’s (45 Mil size) radiant fluxes are measured at 416mW at 350mA current injection, 787mW at 700mA, and 1025mW at 1A for the 392 nm wavelength, respectively. In addition, the company notes that it's hexagonal "Honeycomb" chip shape offers a higher extraction efficiency when packaged with a circular lens as a result of the near circular beam profile.