ENGAGE

Epitaxial Nanostructured GaAs on Si for next Generation Electronics. The heterogeneous integration of III-V materials into a mainstream Si-based CMOS platform offers tremendous prospects for future high-speed and low-power logic applications. The ENGAGE project aims to (i) develop nanostructured high-k/III-V on Si; (ii) investigate novel nanostructured buffer layers to reduce defect densities on the surface of the epilayer; and (iii) study and improve the structural and electrical properties of metal-gate/high-k/III-V MOS devices fabricated using III-V materials grown on Si.

The key challenge lies in the significant lattice mismatch between the Si substrate and the III-V over-layers (4.1% mismatch between Si and GaAs). High extended defect densities (misfit and threading dislocations) are generated in the epitaxial layers due to the large lattice mismatch. There is an immense challenge in using III-V materials on Si to fabricate CMOS devices because the tolerance to dislocations is very low (<104 cm-2).

The ENGAGE activities at the NPL are coordinated by Prof. Patrick McNally, alongside Dr. Nick Bennett and Chiu Soon Wong.

Sonex Metrology (Spin out)

Photoacoustic techniques have long been used for material characterisation. Their strength lies in their sensitivity to both optical absorption and thermal transfer properties of the sample under test. The absorption of intermittent light initiates thermal diffusion waves, upon reaching the sample surface these give rise to pressure waves which are detectable via microphonics.

Analysis of the amplitude and phase (relative to the incident light) of the acoustic signal allows sensitive detection of damage, cracks, interfaces, delamination and a host of other material inhomogenities. The subject of Sonex Ltd. is the application of photoacoustic microscopy to the detection of cracks and bevel edge damage within production scale silicon wafers.

Copper Halides (CuHa)

Optoelectronic devices operating in the energy range of > 3 eV remain an important area of research. The gamma-Copper Halides (CuCl, CuBr and CuI) are ionic I-VII compounds with zincblende structure at room temperatures and are direct bandgap semiconductors with bandgaps in the 3-3.4 eV range.. The NPL group is a world leader in the development of the Copper Halides for optical applications, from development of electroluminescent devices based on CuHa, potential solar applications to the VLS type growth of CuHa microstructures.