Plasma cleaning semiconductor surfaces removes native oxides, carbon contamination, and dangling bonds from GaN and Ga₂O₃ at low temperatures, improving ohmic contact resistance and device reliability without the thermal damage that traditional processing causes.
Why Surface Preparation Is the Bottleneck Nobody Talks About
GaN and Ga₂O₃ get a lot of attention for the right reasons. GaN’s 3.4 eV bandgap and Ga₂O₃’s wider 4.5 to 5.3 eV range put them in a different league from silicon for high-power and high-frequency applications.
Higher breakdown voltages, lower on-resistance, better efficiency at elevated temperatures — the performance case is well established.
What gets less attention is what happens at the surface during fabrication. Epitaxial growth and device processing leave behind native oxides, carbon residues, and oxygen contamination sitting right at the interface where metal meets semiconductor.
They scatter carriers, increase contact resistance, and push up the Schottky barrier height in ways that limit the device no matter how good the bulk material is.
Wet-chemical cleaning handles the obvious contamination but leaves surface states and dangling bonds behind. Those show up as devices that underperform their specifications and degrade faster than they should.
What RF 13.56MHz Plasma Actually Does to the Surface
A radio frequency vacuum system at 13.56 MHz generates plasma where ion density and ion energy can be tuned independently. That independent control is what matters. You can dial in enough energy to break contaminant bonds and displace surface particles without pushing deep enough into the lattice to create damage.
Two things happen at the surface simultaneously:
- Chemical reaction: Radical species attack contaminant bonds directly, converting them into volatile byproducts that get pulled out of the chamber.
- Physical sputtering: Ion bombardment clears what the chemistry misses, including inside high-aspect-ratio features where wet cleaning cannot reach.
For GaN cleaning, nitrogen-based or Ar/H₂ plasma strips native gallium oxide and carbon contamination at temperatures far below what thermal methods require. GaN does not tolerate high temperatures well, so this matters more than it might seem.
For gallium oxide plasma treatment, low-power argon plasma introduces controlled oxygen vacancies into the Ga₂O₃ surface. Those vacancies improve electron conduction and bring contact resistance down.
Keylink’s VL-10-A vacuum plasma system runs at RF 13.56MHz with a working vacuum between 10 and 100 Pa, supporting O₂, Ar, H₂, N₂, CF₄, and other process gases. The same platform handles both GaN and Ga₂O₃ preparation without reconfiguring hardware. Our full vacuum plasma system range covers additional configurations for different production requirements.
The Problem With Thermal Processing for These Materials
Thermal annealing works well enough for silicon. For GaN and Ga₂O₃, it creates more problems than it solves.
Removing native oxides from GaN thermally requires temperatures above 850°C, past the point where GaN starts to decompose. Rapid thermal annealing introduces stress that blurs the heterostructure interfaces that make these devices useful. Dopants diffuse when they should not.
Ga₂O₃ has its own sensitivity. Its stoichiometry, specifically the oxygen vacancy concentration, determines its electrical behavior. High-temperature processing does not give fine control over that.
Low-temperature plasma processing sidesteps all of this:
- Dopant profiles stay where they were put because the thermal budget stays low.
- Heterostructure interfaces remain intact without differential thermal expansion driving stress into the layers.
- Nanostructures and high-aspect-ratio features survive because the process requires no damaging heat.
- The Ga/N ratio on GaN stays within the 1.0 ± 0.04 range that clean ohmic behavior requires.
Ohmic Contact Improvement and Wafer Surface Activation
Clean the surface properly and the contact performance follows. Ohmic contact improvement comes from removing the native oxides and surface states that force current to tunnel through insulating layers instead of passing through a well-defined metal-semiconductor junction.
Key results from plasma surface preparation:
- Ga₂O₃ devices treated with Ar/Cl₂ plasma show contact resistivity reduced by more than a factor of two compared to untreated samples.
- GaN HEMTs treated with remote NH₃ plasma see output current increase by 20 to 30%, with measurable improvement in current slump and gate leakage.
- Ga₂O₃ FETs prepared with Ar plasma pre-treatment reach high-performance specifications without post-metallization annealing.
Wafer surface activation also controls stoichiometry going into metallization. For HEMT and Schottky barrier diode fabrication, that precision at the interface is often what separates devices that pass electrical characterization from those that do not.
Keylink applies the same activation principles across industries. Our resource on plasma cleaning for smartphone housing adhesion shows how surface activation translates into measurable results across different materials.
What This Means for Long-Term Compound Semiconductor Reliability
Getting a device to spec at initial test is one thing. Keeping it there through subsequent fabrication steps, packaging stress, and years of operation is another.
Plasma-prepared surfaces are smoother and more chemically stable than thermally processed ones. They do not develop the defect states during downstream processing that gradually degrade electrical performance. For GaN and Ga₂O₃ devices going into automotive inverters, 5G base stations, and industrial power conversion, compound semiconductor reliability over time is not optional. It is a qualification requirement. Contact us to discuss vacuum plasma solutions for your compound semiconductor application.
