How to sputter indium gallium nitride at low temperatures

Physical vapor deposition through sputter technique

According to a new article published on the Applied Physics Letter, an authoritative publication covering sputter and other deposition technologies, a group of researchers from both the University of Tokyo and the CREST technology agency led by Dr. Eiji Nakamura has proven a strong reduction in the temperature used to sputter indium gallium nitride over a glass substrate using a process called pulsed sputter deposition.

The team aims at creating a new and revolutionary method to sputter InGaN for LED applications combining the newly developed InGaN thin film deposition by PSD with the use of a graphene buffer layer on an amorphous substrate.

The Mg-doped GaN layers have been deposited over a semi-insulating GaN at 480°C, the team measured a p-type conductivity with hole concentration 3.0×10^17.

The application aimed for is InGaN light emitting diodes (LEDs), where low-temperature InGaN deposition is part of the required process.

Until now, you could sputter InGaN over silicon or other substrates by chemical vapor deposition (CVD), with the issue that CVD usually requires deposition temperatures of over 1000°C and most substrates can not withstand such heat.

For example, glass can withstand temperatures up to 500°C, as it softens at 550°C or over depending on glass type.

The new technique will allow to sputter on glass substrates, possibly at industrial scale, on large areas up to few squared meters.

The method created by the Japanese group of researchers has been able to achieve such low temperature deposition thanks to the pulsed sputter process that allows the deposited metals to have an enhanced surface migration of the growth precursors.

Moreover, at temperatures under 500°C it is usually very challenging to achieve p-type conductivity by magnesium doping; the team however used a particular stoichiometric ratio.

The film showed a surface roughness of 0.67nm and a good surface morphology with less defects than usual CVD-deposited InGaN thin films.

Thicknesses from 30nm to 300nm have been tested, measured internal quantum efficiency was at about 24%.

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