A breakthrough in high-speed, eye-safe LIDAR is made possible by heavy-metal-free quantum dots

[Lurker]

There are many different frequencies of light that reach Earth, some of which are visible to us and others of which are not. Because of its special characteristics, shortwave infrared (SWIR) stands out among these frequencies and is very helpful for Light Detection and Ranging (LIDAR) systems.


Like SONAR, which utilizes sound waves to determine distances, LIDAR employs laser pulses.

The danger of SWIR waves is that they do not reach the retina through the cornea and lens of the human eye. SWIR is therefore eye-safe and perfect for real-world uses like LIDAR systems.

A novel technique for creating silver telluride (Ag₂Te) colloidal quantum dots has been demonstrated by researchers at the Institute of Photonic Sciences (ICFO). In LIDAR systems, quantum dots are employed as light detectors, also known as photodetectors.

The new technique overcomes the drawbacks of conventional SWIR photodetectors, which employ hazardous heavy metals like lead or mercury in their quantum dot constituents.

A more eco-friendly substitute, silver telluride colloids, has already been studied for application in quantum dots. Despite their potential, a number of barriers prevent them from being widely used.

By refining the surface engineering of silver telluride colloidal quantum dots to extract maximum efficiency while being environmentally benign, the current work tackles these issues.

Quantum dots and their toxicity

The diameters of quantum dots, which are tiny semiconductor particles, range from 2 to 10 nanometers. A human hair's breadth might accommodate about 15,000 quantum dots placed side by side for comparison.


A quantum dot contains trapped electrons. The distinctive electrical and optical characteristics observed are caused by these quantum confinement effects.

Because of their inherent stability and optoelectronic (light and electrical) qualities, hazardous metals are a desirable choice for their components.

Even though there are safer substitutes, such as silver telluride colloids, their efficacy in detecting both strong and dim light is hindered by noise, long reaction times, and a narrow light detection range.

Engineering the surface
The researchers used two approaches to these problems.

They began by refining the synthesis of colloidal quantum dots made of silver telluride. They were able to eliminate surface imperfections on semiconductor particles, which are known to reduce efficiency, by refining the procedure.

The invention occurs in the second step, which takes place after synthesis. Following the synthesis, scientists treated the quantum dot's thin layer with silver nitrate.

By introducing contaminants into the quantum dots through the application of silver nitrate, the doping procedure modifies the electrical characteristics of the dots.

The silver nitrate in this instance transformed the quantum dots from p-type semiconductors to n-type semiconductors. The p and n show whether the current flowing through the material is caused by positive or negative charges.

The n-type quantum dots do not have the problem of high dark current and poor performance as the p-type does.

Applications of LIDAR that are eye-safe
The SWIR photodetector composed of colloidal quantum dots of silver telluride was tested by the researchers.

By drastically lowering the dark current, the photodetector improved accuracy and decreased noise. The gadget demonstrated improved light detection efficiency, collecting light of a certain wavelength with a 30% efficiency rate.

Additionally, the detector can measure distances precisely because of its fast response time of only 25 nanoseconds. Lastly, a far greater range of light intensities may be handled by the detector.

source: interestingengineering