The Department of Electronic and Electrical Engineering at UCL was formed by Dr J. A. Fleming in 1885 and is the first Electrical Engineering Department founded in the UK. The Department is one of the leading research-led departments in its subject area worldwide, with 40 Academic Staff, 62 Research Staff, and over 100 Doctoral Research Students. Each year the Department produces around 250 Publications and 5 filed Patents. UCL has recently invested £ 2.5 million to for Molecular Beam Epitaxy (MBE) facility with the capacity to grow As-, P-, and Sb-based III-V compound materials, and wide range characterisation facilities for epitaxial materials and devices, such as High-Resolution X-ray, Photoluminescence (PL) Mapping system, AFM and SIMS. Since 2006, UCL has also invested over £ 20 million in the state-of-the-art III-V device processing facilities, including focused Ion beam processing, e-beam lithography, wet etching, dry etching (ICP), dielectric deposition, and metallisation equipment. All these state-of-the-art facilities at UCL and London Centre for Nanotechnology (LCN) are available for this project.

MBE facility at UCL

Role in the project 

UCL MBE Research Group’s main expertise that will be brought to the project concerns the III-V material regrowth on III-V/SiO2/Si template. In WP3 UCL will work with III-V Lab and CEA, targeting a new generation of high density PICs through the heterogeneous integration of III-V on silicon. The detailed objectives in WP3 (Direct Growth on Template) include:

• Demonstration of high quality III-V materials, successfully regrown on InP and GaAs bonded buffer layers on SOI substrates, with surface roughness < 1 nm.
• First QD DFB lasers on silicon using regrowth on GaAs/SiO2/Si template with room temperature output power > 20 mW and operation up to 80°C.
• Selective area growth of active MQW heterostructures for the demonstration of a four channel DFB lasers with wavelength emission spaced 20 nm apart, from 1271 to 1331 nm.

WP3 (Direct Growth on Template

• Task 3.1: Growth of III-V buffer layer on III-V/SiO2/Si template. In this task, high-quality III-V buffer layers will be grown on the III-V/SiO2/Si templates developed in WP1. Different InP and GaAs buffer layers will be prepared on III-V/Si wafers. Surface morphology, the most critical property of buffer layers, will be investigated by Atomic Force Microscope (AFM) at UCL (GaAs buffer) and III-V Lab (InP buffer).

• Task 3.2: Structural and optical characterizations of epitaxial QW and QD materials grown on III-V/Si wafers. The regrowth conditions of III-V QW and QD structures will be finely tuned in the 4-inch MOVPE reactor at III-V Lab and the 3-inch MBE reactor at UCL. Material quality will be carefully characterised through x-ray diffraction, PL measurements, and AFM on dedicated test structures.
• Task 3.3: Growth on GaAs/SiO2/Si template: demonstration of high-performance QD Fabry-Perot and DFB lasers. UCL will work on the growth and fabrication of standard broad-area InAs/GaAs QD lasers. Broad-area laser devices will be processed first at UCL to assess the material qualities for laser devices. The same laser structures will be fabricated on III-V/Si substrates from WP1 and GaAs substrates. The laser performance will be compared between devices grown on III-V/Si and GaAs wafers, to validate the bonding technology developed in WP1. 

Designs for the QD DFB laser structures will be developed at UCL and III-V Lab. The Bragg grating for the DFB lasers will be etched on the silicon waveguides. Then, the DFB devices will be fabricated and tested. In this task, we aim to demonstrate the first silicon-based QD DFB lasers with operation up to 80 °C with room temperature output power > 20 mW.

• Task 3.4: Growth on InP/SiO2/Si template: demonstration of a CWDM transmitter

The task will focus on the selective area growth (SAG) approach. On InP substrates, SAG has demonstrated its high potential for PICs, with large wavelength shift of juxtaposed devices. In this project, the InP on SOI templates will be patterned with dielectric masks for SAG, aiming at the integration of four DFB lasers, with wavelength emission spaced 20 nm apart, from 1271 to 1331 nm. Moreover, the InP/SiO2/Si template will be exploited to build MOSCAP type Mach-Zehnder modulators.

The 4 channels will be combined to a single output waveguide through a wavelength multiplexer already developed by III-V Lab and CEA on the SOI platform. The final target is to demonstrate the complete PIC, with more than 1 mW per CWDM channel at the output of each Mach- Zehnder modulator.

Schematic diagrams of CWFM transmitter, integrating 4 DFB lasers with the gain region fabricated