Novel photodetectors based on nanomaterials: devices and applications
This joint PhD project will be based at The University of Melbourne with a 12 month stay at the Shanghai Jiao Tong University.
Recent advances in nanomaterials present opportunities for novel photodetector devices and for imaging and spectroscopy systems based on them. Much of the previous work in this ﬁeld has been in the visible and near- infrared spectral bands. The mid- to long-wave infrared spectral range has been far less explored, despite the abundant applications in this wavelength range. Here, we will investigate novel photodetectors for this spectral range based on new nanomaterials (primarily by SJTU) and nano-optics (primarily at UoM). We will furthermore develop new imaging and spectroscopy systems by combining these devices with spatial light modulators.
We propose a research program on the development of IR photodetectors based on nano-optics and ultra-thin materials. For the latter, we will investigate what are known as two-dimensional (2D) materials. Such photodetector devices present the opportunity for room temperature operation. Conventional infrared photodetectors generally require cooling. This is because, by deﬁnition, infrared radiation comprises photons with small energies. It is thus generally detected by semiconductors with small bandgaps. In such materials, carriers are thermally generated at high rates at room temperature, degrading the signal-to-noise ratio (SNR). Cooling (e.g. by liquid nitrogen) mitigates this, but adds substantially to size, weight, power consumption and cost.
We propose to develop new types of photodetectors that combine semiconductors with small bandgaps with 2D materials and with nano-optical structures. These will operate using a principle termed “photogating”. Light will be absorbed by the small bandgap semiconductor material, resulting in the generation of electron-hole pairs. These carriers will in turn modify the conductance of the 2D material. It will thus be possible to detect the infrared radiation by monitoring the resistance of the 2D
material. The fundamental advantage of this conﬁguration is that the 2D material will made from a material (e.g. molybdenum disulphide) that has a much larger bandgap than the narrow bandgap semiconductor material (in which the light is absorbed). The device will therefore have a much lower dark current than the conventional alternative conﬁguration, in which the conductance of the small bandgap material is measured.
As noted above, the proposed devices will also incorporate nano- optical structures. These will serve two purposes. The ﬁrst purpose is to implement the “optical immersion” principle. Speciﬁcally, we will minimise the volume of the photodetector’s active material (to reduce noise) while maintaining its light gathering ability (and thus signal) via the use of the nano-optical structures to collect the light and concentrate it within the active material. The second purpose is to achieve photodetector devices with “tailored” responsivity spectra. We will show that arrays of such detectors (each with a diﬀerent responsivity spectrum) will enable miniature spectrometer chips (using computational spectral reconstruction) & multispectral imagers.
Next we summarise the plan of work to be undertaken at each institution. The ﬁrst 12 months of the project will be undertaken at the University of Melbourne. In this phase, the PhD student will use numerical electromagnetics simulations to design the nano-optical structures that collect and concentrate light into the active region of the photodetector. The PhD student will furthermore fabricate these structures at the Melbourne Centre for Nanofabrication (MCN) and characterise them optically in the Crozier Group laboratory at the University of Melbourne. The next phase will be performed at Shanghai Jiaotong University and be of 12 months’ duration. During this phase, the PhD student will perform experiments to demonstrate the photogating eﬀect. This will be done by fabricating devices at Shanghai Jiaotong University and testing them. These devices will furthermore incorporate the nano-optical structures developed during the ﬁrst year.
The last phase will have a duration of 18 months and be performed at the University of Melbourne. During this phase, the PhD student will incorporate the newly demonstrated photodetector into a single pixel camera or into a microspectrometer, and thereby demonstrate an imaging or a spectroscopy application.
In the project plan described above, the work to be undertaken at the University of Melbourne mainly relates to nano-optics and to building an optical system (for imaging or spectroscopy) based on the novel photodetector device. For the work to be undertaken at Shanghai Jiaotong University, the work is mainly to do with semiconductor devices. This is due to the fact that the main activities of the Crozier Group at the University of Melbourne are in nano-optics and optical systems, while the Yaping Dan group at Shanghai Jiaotong University concentrates on semiconductor devices.
The project will be complemented by the project on Mid-infrared photodetectors based on atomically thin 2D materials and the collaboration will ensure a successful completion of the project.
Professor Kenneth Crozier (The University of Melbourne)
Associate Professor Yaping Dan (Shanghai Jiao Tong University)