Scientists have found an easy way to lower electrical resistance in gallium nitride (GaN) semiconductors, which could lead to more efficient LEDs, electric vehicles, data centers, and other high-power electronics.
Researchers at Nagoya University in Japan achieved this by applying an ultra-thin layer of magnesium to improve one of the challenging electrical contacts in GaN. Their discoveries were recently published in Applied Physics Letters.
Semiconductor devices like LEDs and transistors are made from two main types of materials. N-type materials predominantly conduct electrons, while p-type materials carry positive charges, or “holes,” which are essentially missing electrons. Both types need effective electrical contacts—called ohmic contacts—that allow current to flow smoothly in and out.
Creating low-resistance contacts for thin p-type GaN has been notoriously difficult for decades. Higher resistance results in more energy loss during operation. The Nagoya team, led by Haitao Wang and Jia Wang, demonstrated that depositing a nanometer-thin magnesium layer onto p-type GaN significantly improved contact quality. After heating the material to 600°C for five minutes, the contact resistance dropped dramatically, measuring between 1 and 3 × 10⁻⁴ ohm-square centimeters—some of the lowest reported values for thin p-type GaN. Importantly, this process didn’t significantly damage or roughen the material’s surface.
Magnesium has a well-established role in GaN technology. Small amounts of magnesium doping have historically enabled efficient p-type GaN, contributing to blue LED development, a breakthrough that was honored with the 2014 Nobel Prize in Physics. However, Mg-doped GaN faces a problem: at room temperature, there are relatively few free holes near the contact boundary, creating an energy barrier that hampers current flow.
One traditional workaround is to add an extra heavily doped GaN layer rich in holes, but this increases production costs and complexity and makes devices vulnerable to damage during manufacturing.
The new approach simplifies the process. Previously, the team experimented with thicker magnesium layers, but heating them caused surface roughness issues unsuitable for thin devices. In this study, they limited the magnesium layer to about 10 nanometers. Interestingly, they found no need for a protective coating to prevent oxidation, as only the topmost magnesium oxidized, leaving enough reactive magnesium underneath.
During brief heat treatment, magnesium diffuses into the surface of GaN, creating a heavily magnesium-doped region. This reduces the electrical barrier, allowing positive charge carriers to pass more easily. The method is cost-effective and adaptable, as it can be done after other device fabrication steps without the need for growing additional layers.
The researchers are now exploring this technique for different applications, including LEDs and transistors for electric vehicles. If adopted commercially, this tiny magnesium layer could make GaN-based devices more energy-efficient and better-performing by minimizing power loss.
