Search
Menu
Meadowlark Optics - SEE WHAT

Solid-State Photodetector May Speed Switching of Optoelectronic Devices

Facebook X LinkedIn Email
An all-solid-state wavelength-dependent bipolar photodetector (WBPD), composed of a single semiconductor, has demonstrated a faster response time than existing WBPDs that are comprised of hetero-nanostructures. The novel WBPD has also demonstrated tunable switching wavelengths.

To speed response time in the novel photodetector, researchers at Toyota Central R&D Labs used a tungsten disulphide film with front and rear ends modified by oxidation and sulpherization. The band structure of the semiconductor film had the ability to increase or decrease at both the rear and front surfaces, which allowed it to form a U (or upside down U) shape, making the film capable of carrying photocurrents with wavelength-dependent switching.

Schematic illustration of the device structure of the WBPD. ?1 indicates shorter-wavelength incident light, ?2 indicates longer-wavelength incident light.
Schematic illustration of the device structure of the WBPD. λ1 indicates shorter-wavelength incident light, λ2 indicates longer-wavelength incident light.

The researchers also exploited the dependency between wavelength and depth of photon penetration in semiconductor material. Because shorter wavelengths are more readily absorbed than long, shorter wavelengths have a higher distribution of excited electrons near the front surface; whereas longer wavelengths have greater distribution at a deeper level of penetration into the material. When drift and diffusion processes are taken into account, this phenomenon causes photocurrents in opposite directions, for short- and long- wavelength incident light.

Cognex Corp. - Smart Sensor 3-24 GIF MR

The researchers showed that the threshold wavelength at which the photocurrent polarity changed could be tuned by choosing a suitable thickness for the device. The device thickness affected the distribution of photoexcited carriers as a result of the wavelength-dependent absorption, allowing tunable switching wavelengths.

In existing WBPD devices, the switchable photocurrent polarity behaviors are caused by differences in the optical properties of the two materials that comprise the device; and the transition wavelengths of the output polarity are limited by the optical properties of the two types of materials. The low carrier mobility in liquid electrolytes, which are used in many current WBPD devices, can slow switching response time.

For current and future optoelectronic devices such as logic gates, extremely high response times will be required. An all-solid-state WBPD (i.e., a WBPD without any electrolytes) may have significant advantages over WBPDs using molecules and electrolytes.

“Optoelectronic sensors that can switch their photocurrent direction based on the wavelength of incident light are an important building block in novel optical logic gates, color sensors, and photocatalysts,” said Takashi Ikuno and Masaki Hasegawa, researchers at the Toyota Central R&D Labs.

The research was published in Applied Physics Express (doi:10.7567/APEX.9.062201).

Published: September 2016
Glossary
detector
1. A device designed to convert the energy of incident radiation into another form for the determination of the presence of the radiation. The device may function by electrical, photographic or visual means. 2. A device that provides an electric output that is a useful measure of the radiation that is incident on the device.
photodetector
A photodetector, also known as a photosensor or photodiode, is a device that detects and converts light into an electrical signal. Photodetectors are widely used in various applications, ranging from simple light sensing to more complex tasks such as imaging and communication. Key features and principles of photodetectors include: Light sensing: The primary function of a photodetector is to sense or detect light. When photons (particles of light) strike the active area of the photodetector,...
photon
A quantum of electromagnetic energy of a single mode; i.e., a single wavelength, direction and polarization. As a unit of energy, each photon equals hn, h being Planck's constant and n, the frequency of the propagating electromagnetic wave. The momentum of the photon in the direction of propagation is hn/c, c being the speed of light.
optoelectronics
Optoelectronics is a branch of electronics that focuses on the study and application of devices and systems that use light and its interactions with different materials. The term "optoelectronics" is a combination of "optics" and "electronics," reflecting the interdisciplinary nature of this field. Optoelectronic devices convert electrical signals into optical signals or vice versa, making them crucial in various technologies. Some key components and applications of optoelectronics include: ...
wavelength
Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.
optical
Pertaining to optics and the phenomena of light.
Research & TechnologyAsia-PacificdetectorphotodetectorphotonoptoelectronicswavelengthopticalphotocurrentssemiconductorsTech Pulse

We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.