New and Emerging Low Dimensional Photonic Devices and Applications

Overview:

Light manipulation and control at the nanoscale is becoming an important feature, mainly due to applications in wireless communications, fiber optics, energy devices, etc. Photon generation at the nanoscale can be highly efficient owning to their low power consumption. Here, we fabricate and test photonic devices and characterize their performance compared to commercially available devices.

Tunable Light Emission at The Nanoscale

Tunable light emission at the nanoscale can be accomplished by doping the material. Various groups have demonstrated this tunable light emission using this technique. Nevertheless, owning to their tunable band gap with the number of layers, layered 2D materials can exhibit tunable photoluminescence. However, the spectral resolution of such technique is limited since this process depends on the intrinsic properties of each number of 2D layer. Using thermal processes, we demonstrate tunable photoluminescence with high spectral resolution. This tunable light emission is caused by the formation of stable black phosphorus oxide, which is an under investigated material. Using our Raman and photoluminescence measurements, the tunability resolution can be as small as 5nm with tunablity bandwidth of between 590-730nm.

Further characterization of this tunable photoluminescence reveals that different compositions of black phosphorus oxide grow on the surface of layered black phosphorus. In fact, this tunable light emission emerges from the tunable band gap of black phosphorus oxide, where this band gap is highly dependent on the oxygen concentration. This tunable light emission can be promising for LED and photonic device applications.

Low-Cost Solution Processed Van der Waals Photovoltaics

Photovoltaic devices based on low dimensional materials are predicted to exhibit a high solar cell efficiency. Due to the high electron mobility and layer tunable band gap, 2D materials can be a promising route for high efficiency solar cells. However, fabrication challenges and environmental effects can significantly degrade the the solar cell behavior. In this work, we fabricate low cost photovoltaics using solution processed nanomaterials. The fabricated solution is then deposited on the desired structure. An advantage these solar cells exhibit is how the solution is integrated with the solar cell structure, where simple Van der Waals deposition techniques are tested. We characterize these different photovoltaics for the best efficiencies possible, which is a step towards low cost energy generation.

Van der Waals Photodetectors

Nanoscale photodetectors can offer exceptional performance for a wide range of wavelengths. Van der Waals materials are one example where room temperature photodetection can be achieved over a large wavelength range. Due to their low dimensionality, quantum confinement, and tunable band gap with thickness, Van der Waals materials can be promising photodetector materials for visible, short wave infrared, mid-wave infrared, and long wave infrared. Moreover, Van der Waals semiconductors only require a simple micro-alignment deposition method and can be electrostatically doped, enabling us to tune the Fermi level of photodetector material. Here, we use exfoliated nanosheets and perform material deposition using our in-house micro-aligner. This deposition method enables us to examine the photodetection mechanism at different incident wavelengths. We perform scanning photocurrent microscopy coupled with Raman microscopy to identify and characterize the active region of the photodetector.

We have demonstrated room temperature, high-gain mid-wave infrared photodetector using Tellurene, which is a newly emerging material. This tellurene photodetector can cover a wide range of wavelengths with high responsivities in room temperature. In our group, we fabricate and characterize different emerging photodetectors using different nanomaterials. We explore new highly efficient photodetectors with high responsivity and methods to optimize photodetector parameters including contact engineering, active region modification, defect-free fabrication techniques.

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