New Fast-Switching, Wavelength-Dependent Bipolar Photodetector

New Fast-Switching, Wavelength-Dependent Bipolar Photodetector
Schematic illustration of the device structure of the WBPD. λ1 indicates shorter-wavelength incident light, λ2 indicates longer-wavelength incident light.

Optoelectronic sensors that switch photocurrent direction, depend on the wavelength of incident light. They are an important building block in novel optical logic gates, color sensors, and photocatalysts. Scientists from Toyota Central R&D Labs have developed the first all solid-state wavelength-dependent bipolar photodetector. This bipolar photodetector has a fast response time and tunable switching wavelength.

Current wavelength dependent bipolar photodetectors are based on liquid electrolytes. This makes its response time slow. It is too slow for future optoelectronic devices and logic gates. There are two materials with different optical properties used to create wavelength-dependent photocurrents carried by an electrolyte. This low carrier flexibility in liquid electrolytes makes slower response time.

Thus, scientists decided to use a semiconductor film with a band structure. This increase or decrease at both the rear and front surfaces by giving the band structure a U or upside-down U shape. Thus, it will capable of photocurrents with wavelength-dependent switching.

This bipolar photodetector gets the wavelength-dependent penetration of photons in semiconductors. Short wavelengths absorbed more quickly as compared to long. Thus, short wavelengths will have a higher dispersion of excited electrons close to the front surface. The dispersion is better immersed at the large wavelength. Thus, for short and long wavelength incident light, this drift and diffusion process causes photocurrent in beyond directions.

By using a tungsten disulphide film, scientists discover this novel approach. This film is modified by oxidation and sulphurization at both front and rear end.

The device’s thickness effects on the dispersion of photoexcited carriers. It because of wavelength based absorption. This allows for tunable switching wavelengths. Its fast response time gives essential advantages to the device by using molecules and electrolytes.