News Feature | February 13, 2017

Perovskite Nickelate Photodetector Powers Itself

By Jof Enriquez
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nanyang
Nanyang Technological University

Researchers have developed a new kind of photodetector that utilizes its built-in semiconducting heterojunction to power itself, rather than rely on external voltage, as typical photodetectors do. Constructing this semiconducting junction from perovskite nickelates – materials that are very sensitive to oxygen content – makes the photodetector broadly sensitive, which makes it ideal for use in next-generation optoelectronic devices.

The heterojunction is built by combining the GdNiO3 (gadolinium nickel oxide) film, sensitive to a wide spectrum of light, with Nb-doped SrTiO3 (niobium-doped strontium titanate) through pulsed laser deposition. The inherent electric field at the GdNiO3/Nb-doped SrTiO3 (GNO/NSTO) p-n heterojunction interface provides the driving force for efficient separation and measurement of photo-generated electrons, negating the need for an external power source.

In Applied Physics Letters, the researchers, led by Junling Wang and Le Wang at Nanyang Technological University in Singapore, described their self-powered, sensitive, and stable PD based on the GNO/NSTO heterojunction: "The device exhibits high sensitivity towards light between 650 nm and 365 nm. Under 365 nm illumination (50 μW/cm2), the optimized device has a responsivity of 0.23 A/W at 0 V bias, and the photo-dark ratio is close to 103 at a light intensity of 0.6 mW/cm2. The high photo-response primarily arises from the built-in field formed at the interface of p-GNO and n-NSTO. Our work extends the potential applications of nickelates."

Moreover, the researchers claim that their device showed no change in performance after six months.

Perovskite creates semiconductors that are very stable and have tunable band gaps, ideal as light-absorbing materials in optoelectronic devices and solar cells. Scientists have discovered that cheap and easy-to-use perovskite is a more efficient alternative to silicon-based solar cells, which topped out at about 25 percent efficiency more than a decade ago.

Because perovskite nickelates are very sensitive to oxygen content, the researchers in Singapore and China were able to tune their electronic structures by varying the oxygen partial pressure during film deposition.

"Our work is novel and confirms that nickelates films have tunable band gaps with changing of the oxygen vacancy concentration, which makes them ideal as light absorbing materials in optoelectronic devices," said Wang in a news release. "Using the self-powered photodetector we designed, we study its photo responsivity using light sources with different wavelengths, with significant photo-response appearing when the light wavelength decreases to 650 nanometers."

Wang's team plans to experiment with different pairings of rare earth elements and nickelates to elicit "exotic phenomena."

"One of the remarkable features of nickelates [...] is the dependence of their physical properties on the chosen rare earth element," said Wang. "Thus far, we have only studied GdNiO3 film, but besides that we can also investigate other "R"-NiO3 films where "R" can be Nd (neodymium), Sm (animony), Er (erbium) and Lu (lutetium) and study their potential applications in the photodetector."

The research was supported by the Ministry of Education, Singapore, the National Basic Research Program of China, and the National Natural Science Foundation of China.