PORTLAND, Ore. Pure carbon atoms based on depositing graphene on gallium arsenide wafers could yield the next generation of high performance semiconductors, according to German researchers.
Investigators at the Physikalisch-Technische Bundesanstalt (Braunschweig, Germany) recently claimed to have imaged graphene on the surface of a GaAs wafer for the first time using an optical microscope.
|Nearly invisible single-carbon atom layers can be made visible using a normal optical microscope if the support layer is designed as an anti-reflection filter. Single-layer graphene is identified inside the marked areas.|
GaAs is widely used in semiconductors that must outperform silicon chips, especially in RF applications where the wavelengths are too short for CMOS. Future carbon-based chips will likely use layers of crystalline carbon--graphene--to outperform silicon, prompting the German researchers to begin investigating ways of depositing graphene on GaAs to achieve a hybrid material with advanced properties.
Earlier this year, Italian researchers sought to sidestep the lattice mismatch between graphene and GaAs by sculpting graphene's crystalline lattice pattern into the surface of a GaAs wafer, endowing the "artificial graphene" with some of the properties of the resulting material. The German lab has since demonstrated that actual graphene can be successfully deposited atop GaAs.
Prior to these advances, most graphene research used silicon wafers coated with silicon dioxide, or silicon-on-insulator, which allowed graphene to be imaged. The depositing of graphene on GaAs wafers has lagged due to the difficulty of imaging the results using standard optical microscopy. The German researchers claim to have solved the imaging problem, opening the door to process engineers working on deposition of graphene on GaAs.
The researchers used an anti-reflective buffer layer of aluminium arsenide (AlAs) between the two materials to solve the imaging problem. Transparent AlAs was vapor-coated in several monolayers, allowing the researchers to grow just the right amount to cause interference effects similar to those caused by standard optical interference filters.
By optimizing multiple layers of GaAs and AlAs atop a doped GaAs substrate using molecular beam epitaxy, the group was able to image exfoliated graphite on GaAs with enough resolution to distinguish single, double and multiple layers of graphene.
The researchers also confirmed their findings with Raman spectroscopy, and are currently characterizing the electrical properties of their graphene-on-GaAs wafers.