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Integrating Dual-Effects for a Versatile Photodector

A team of scientists from the State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, develop a photodector with both photovoltaic and bolometric effects.

Photodectors are also known as photosensors that senses light or other electromagnetic radiation. Within the p-n junction of a photodector, light photons are converted into current. New and improved photodectors that are able to perform better in relation to response rate, broader spectrum, detectivity, and other special functions such as polarization detection and two-colour detection are in high demand.

However, there are limitations in the use of conventional materials and the single detection mechanisms face the challenge of losing its competitiveness in the market. Introducing new materials and integrating multiple detection mechanisms could create a photodector with better comprehensive performance, bringing it to the next generation of photodectors.

In a research published in Light Science & Application, by a team led by Professor Wang Jianlu from the State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, China, demonstrated the development of a versatile photodector that intergrates photovoltaic and bolometric effects. It is a heterostructure composed of molybdenum telluride and vanadium dioxide. Molybdenum telluride acts as a transferable semiconductor and vanadium dioxide acts as the bolometric material.

Based on this structure, the device achieves three different functional modes including, p-n junction, Schottky junction, and the bolometer. The flexibility to switch between three modes makes it a potential candidate for next-generation photodetectors from visible to long-wave infrared radiation (LWIR). This dual-mechanism integration strategy opens up a novel development path to advanced optoelectronic devices.

The scientists summarised the operation of the newly developed photodector based on the three different modes it is able to achieve.

In the p-n junction mode, when the molybdenum telluride is transferred to the top of vanadium dioxide at room temperature, a space charge region (SCR) appears at the interface of vanadium dioxide and molybdenum telluride as the carriers are swept out by the built-in electric field.

Electron-hole pairs are generated in the SCR by electron transition under light illumination. Because of the photovoltaic effect, the electrons and holes are separated and collected by electrodes, which accounts for the source of photocurrent. To minimize the dark current, this mode are works at zero bias. The separation process is driven by built-in field, the response rare is rather fast than other detection mechanism. Additionally, vanadium dioxide is a narrow bandgap semiconductor, the p-n junction mode can response to light radiation of 2 μm.

In the Schottky junction mode, vanadium dioxide is a typical phase transition material with metal-insulator-transition (MIT) near room temperature (340 Kelvin). The device transforms to Schottky junction when vanadium dioxide become metallic at the temperature exceeding MIT temperature. Although the dark current is increased compared to room temperature, the device is still capable of photodetection from visible to near infrared radiation. This mode can be used industrial inspection as high as 400 Kelvin, is an extension of the traditional detector.

Finally, in the bolometer mode, vanadium dioxide is traditionally used in the bolometer industry because of its large temperature coefficient of resistance (TCR). When the forward bias is larger than built-in electric field, p-n junction can be considered as a resistor. Therefore, the device transforms into a bolometer. The bolometer absorbs the heat energy and is not selective to the wavelength of radiation, therefore, the device can be used to detect mid-wave infrared radiation (MWIR) and LWIR. [APBN]