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Low Resistance, p-Type Ohmic Contacts for Energy Efficient Devices (Group III-Nitride Semiconductors)




Scientists at Berkeley Lab and the University of Nottingham have developed a method for reproducibly fabricating a low-resistance ohmic contact to p-type group III-nitride semiconductors. These contacts can significantly improve the energy efficiency of several devices, including light emitting diodes (LEDs), solar cells, and laser diodes.

The contact is formed by adding a thin, amorphous semiconductor layer between a p-doped group III-nitride, for example, a gallium nitride [GaN]) semiconductor and a metal contact. This additional layer consists of a group III-nitride alloy such as GaNAs that can be heavily doped with Mg, a p-type dopant. This significantly reduces the thickness and the height of the barrier for the charge carrier transfer from GaN to the metal contact. The resulting ohmic contact has a resistivity at least one order of magnitude lower than that traditionally found on p-type doped GaN.

The scientists formed the GaNAs materials by molecular beam epitaxy and varied the thickness, composition (As to N ratio), and amount of Mg dopant within the intervening contact layer. This allowed them to optimize the contact for different applications, photovoltaics vs. LEDs, for example, and achieve the lowest possible resistivity. In addition, because the intervening layer is an amorphous rather than crystalline semiconductor, it offers the advantage of not needing to be lattice-matched with the underlying GaN semiconductor.

Group III metal-nitride materials such as GaN, InGaN, and AlN are currently used in a variety of commercial technologies. However, their applications have been limited by difficulties in making low resistance, p-type ohmic contacts. The performance of devices, including laser diodes, high brightness LEDs or high power switches, requiring high electric currents is adversely affected by heating at ohmic contacts because of the contact resistance. The Berkeley Lab invention overcomes this challenge by providing a method to fabricate low resistance contacts that can be optimized for different device applications.

DEVELOPMENT STAGE: Proven concept.

STATUS: Patent pending. Available for licensing or collaborative research.


Stable and Highly Conductive Transparent Semiconductors, IB-2957

Novel Structured LED and OLED Devices, IB-2230

Co-implantation of Group VI Elements and Nitrogen for the Formation of Non-Alloyed Ohmic Contacts for n-type GaAs, IB-1609


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