Movies of carbon nanotubes as ultrasensitive photodetectors: progress and challenges

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are being used to develop a third generation of optimized short-wave infrared photodetectors that will improve pixel size, weight, power consumption, performance and cost over photodetectors made from traditional materials.

Ultra-sensitive shortwave infrared photodetectors, which detect a subset of shortwave infrared light wavelengths beyond the visual spectrum, have many potential applications, including night surveillance, navigation during adverse weather conditions, fiber optic communications and semiconductor quality control.

Shortwave infrared photodetectors have traditionally been made of III-V materials such as indium gallium arsenide (InGaAs). However, InGaAs photodetectors are expensive and current research into alternative photodetector materials, such as s-SWCNTs, will ideally reduce the cost of shortwave infrared photodetectors while increasing both performance and efficiency.

A team of leading scientists from Peking University outlined the current technology and challenges associated with developing s-SWCNT films into shortwave infrared photodetectors to drive additional research and applications of the technology. Current advances in solution purification technology will facilitate the development of high-purity s-SWCNT films suitable for homogeneous and high-performance optoelectronic devices and large-area light-sensing and processing applications, including photodetectors.

Further optimization of film purity, thickness, brightness and array alignment must be achieved before s-SWCNT films will match or exceed the performance level of traditional, more expensive photodetectors made from InGaAs or similar materials.

The team published their review in the March 16 issue of Nano research energy.

“Assessing the progress of the s-SWCNT film photodetectors can clarify the current research status, challenges, and applications of s-SWCNT film photodetectors and optoelectronic integration,” said Sheng Wang, one of the review’s authors and an associate professor at the School of Electronics at Peking University, China.

“We outlined the s-SWCNT technology in three sections: (1) the current research status of the s-SWCNT film photodetectors, (2) the current research status of monolithic/three-dimensional optoelectronic integration based on s-SWCNT film photodetectors, and (3) the requirements of s-SWCNT film and device structure for ideal s-SWCNT film photodetectors and optoelectronic integration,” Wang said.

“The next step in the field is to improve the performance of s-SWCNT film photodetectors by optimizing the s-SWCNT films and device structure. For the s-SWCNT film optimization, the semiconductor purity of a uniform s-SWCNT film should be more than 99.9999%,” said Wang.

Achieving these levels of purity is not a trivial matter. Early purification methods attempted to burn off s-SWCNT impurities after films had grown, but resulted in films with many defects. Since then, conjugated polymers have been used to purify s-SWCNTs not only from impurities, but also by their diameter, as different diameters of s-SWCNT determine what wavelengths the films can detect. Recently, a sorting process has achieved the s-SWCNT purity levels required for high-performance electronics.

Optimization is also required in the preparation of the s-SWCNT film, including thickness, clarity, and alignment. Many methods have been developed to grow s-SWCNT films, but deposition and dip coating methods are often preferred due to their simplicity, stability, and the homogeneous films they produce. A scalable and efficient method of dip coating controls s-SWCNT deposition by simply changing the number of times a substrate is lifted from dispersed s-SWCNTs from an organic solvent and changing the speed of each lift.

The electronics field recognizes the potential of s-SWCNTs as a suitable material for high performance shortwave infrared detectors, but a significant performance gap exists between traditional photodetectors, made from materials such as InGaAs, and s-SWCNT film photodetectors. “The ultimate goal is to optimize the performance of s-SWCNT film photodetectors to be comparable to commercial photodetectors at a lower cost,” said Wang.

The researchers believe this performance improvement and cost reduction will result in the integration of more shortwave infrared photodetector films into devices and the development of new optoelectronic applications in the future. The field also strives to integrate high-performance carbon nanotubes into electrical circuits.