ERC Researchers Overcome Prior Accepted Limits for Important Materials

Achievement date: 
2013
Outcome/accomplishment: 

Researchers affiliated with the NSF-funded Engineering Research Center (ERC) for Quantum Energy and Sustainable Solar Technologies (QESST), which is headquartered at Arizona State University, have demonstrated extremely high-hole concentrations in gallium nitride (GaN) and indium gallium nitride (InGaN), overcoming previously accepted limits for this material system.

Impact/benefits: 

The new GaN and InGaN materials allow for drastic improvement in many devices, such as light-emitting diodes (LEDs) and transistors that have already made significant impacts in their respective markets. It also, for the first time, demonstrates the feasibility of GaN and InGaN for use in high-efficiency and multi-junction solar cells.

Explanation/Background: 

Low-hole concentrations have previously been blamed as a major performance-limiting factor in LEDs and transistors, making InGaN not viable for use in multi-junction solar cells due to the lack of a tunnel junction. Using a unique growth method, researchers at Georgia Tech were able to grow GaN and InGaN layers with room-temperature hole concentrations nearly 40x larger than generally accepted limits for these materials [Appl. Phys. Lett. 101, 082106 (2012)]. In the newly grown films, more than 50% of the magnesium is active, compared to the 1-5% activation in traditional layers. The deeply degenerate GaN and InGaN films exhibit minimal temperature dependence, which allows more robust devices to be used across a wide range of temperatures and applications.