Indium antimonide (InSb) is a semiconductor with an exceptionally narrow bandgap of 0.17eV. As a result, optoelectronic devices such as LEDs and photodiodes, when fabricated using InSb, operate in the mid-range of the infrared spectrum. Recent advances in quantum well structures have enabled InSb devices to operate at room temperature, which in turn has enabled applications such as thermal imaging, infrared photovoltaics and mid-infrared transmission-based gas sensing.
The Quantum Devices group is aiming to improve the sensitivity and efficiency of InSb mid-infrared LEDs and photodiodes. In particular, the use of nano-antenna structures has demonstrated significant improvements in photodiodes made with other materials and their application to InSb is being explored within the group. Nano-antennas are physical patterns formed on the surface of the devices which focus incoming light into a small surface area and depth, resulting in superior response. The work of the Quantum Devices group includes CAD modelling and practical work, aiming to not only demonstrate devices with superior efficiency and sensitivity but to do so using a fabrication process which can be readily adapted into large-scale industrial manufacture.
Coarse inspection of nano-antenna structures under optical microscope
Due to the compound nature of III-V semiconductors, the interfaces they form with other materials tend to be low-quality. These poor interfaces give rise to excessively large leakage currents in devices and poor channel mobility in MOSFETs. In addition, the exciting new devices made possibly by InSb’s exceptional properties, such as spin-based devices, require high-quality dielectrics for good electric field control.
The quantum devices group is exploring techniques for depositing and processing dielectrics on narrow bandgap III-V materials, with a view to improving interfaces. Working in conjunction with the atomic layer deposition (ALD) capabilities at the University of Liverpool, we aim to reduce interface trap state density, as well as oxide leakage current and device edge leakage current.
Interface test devices being probed
While the industry for silicon is well established, with large wafer sizes and high-throughput process technology, III-V materials remain a niche industry. As such, the capability to grow III-V materials such as InSb on existing wafers is critical for their development. Working in conjunction with the Department of Chemistry at Warwick, the Quantum Devices group operates a molecular beam epitaxy (MBE) growth tool. Using this capability, the Quantum Devices group are capable of forming quantum well structures using layers of AlInSb, allowing InSb devices to operate at room temperature. The MBE capability is also being used to explore the addition of bismuth to narrow bandgap III-V materials, the prospects of growing InSb layers on silicon wafers and the use of III-V semiconductors in spintronic devices.
Clean semiconductor wafer with a layer of InSb grown using MBE
Simulation of nano-antenna structures
Patterns etched in aluminium oxide dielectric
Atomic planes in epitaxial InSb viewed by atomic force microscope