Mid-infrared photodetectors based on atomically thin 2D materials

This joint PhD project is based at the Shanghai Jiao Tong University with a 12 month stay at The University of Melbourne.

Project description:
Mid-infrared photodetectors can find a wide range of applications in many fields. The existing mid-infrared photodetectors have to operate at cryo temperature, as a result of which systems for mid-infrared photodetection and imaging are often bulky and expensive. Here, we propose to develop room temperature mid- infrared photodetectors based on atomically thin MoS2 monolayers.

In this study, we propose to develop room temperature mid-infrared photodetectors based on atomically thin MoS2 monolayers. These photodetectors will in turn be used to realize a miniature infrared spectrometer chip. Atomically thin monolayers are poor light absorption materials. To enhance the light absorption, we propose to place the monolayer on a bulk HgCdTe crystalline substrate that absorbs mid-infrared light. The light absorption in HgCdTe substrate with a junction (induced by surface charges or doping) will create a photovoltage gating on the MoS2 monolayer. We will read this out electrically, i.e. by measuring the change in conductivity of the MoS2 monolayer. Since the MoS2 monolayer has a wide bandgap, it can operate in the subthreshold region, meaning that the dark current will be suppressed. The fact that the MoS2 monolayer is atomically thin will allow the weak photovoltage to gate the monolayer in an effective manner and induce a large conductivity change.

We anticipate that this will result in this device having a very high gain (>10^8) and a high photoresponsivity.  One might expect that this approach would lead to the device having high dark current and slow response times. The   dark current can be suppressed by operating the MoS2 monolayer in the subthreshold region. The speed can be improved to ~ 1kHz by lowering the gain a little, e.g. to 10^6. We believe that the planned bandwidth (of 1 kHz) would be adequate for most real applications of these devices (e.g.  imaging). By collaborating with Prof. Kenneth B. Crozier at the University of Melbourne, we aim to develop miniaturized mid-infrared spectral analyzers by integrating spectral filtering structures onto our photodetectors.

In the first year, the PhD student will take required courses and perform optoelectronic simulations on the mid-  infrared photodetectors at Shanghai Jiao Tong University. In the second year of the project will be conducted at the University of Melbourne. The PhD student will use numerical electromagnetics simulations to design the nanostructures that spectrally filter and concentrate light into the active region of the photodetector. The designed structures will be further fabricated at the Melbourne Centre for Nanofabrication (MCN) and characterized optically in the Crozier Group Laboratory at the University of Melbourne.  In the third year, the PhD student will return to Shanghai Jiao Tong University and fabricate and electrically characterize the MoS2 monolayer photodetectors. In the fourth year, the PhD student will incorporate the newly fabricated photodetectors into a micro-spectrometer.

The project will be complemented by the project Novel photodetectors based on nanomaterials: devices and applications and the collaboration will ensure a successful completion of the project.

Supervision team:

Associate Professor Yaping Dan (Shanghai Jiao Tong University)

Professor Kenneth Crozier (The University of Melbourne)