How a UVC LED Works
How UVC LEDs truly function is a popular query from businesses looking at UVC LEDs for disinfection purposes. In this article, we describe the workings of this technology.
Principles of LEDs in general
When a current is conducted through a light-emitting diode (LED), a semiconductor device, it emits light. While extremely pure, defect-free semiconductors (also known as intrinsic semiconductors) typically conduct electricity very inefficiently, dopants can be added to the semiconductor to change its conductivity to either positively charged holes (n-type semiconductor) or negatively charged electrons (p-type semiconductor).
A p-n junction, where a p-type semiconductor is placed on top of an n-type semiconductor, makes up an LED. When a forward bias (or voltage) is given, holes in the p-type material are pushed in the opposite direction (as they are positively charged) towards the n-type material.
Similarly, electrons in the n-type region are pushed towards the p-type region. The electrons and holes will combine at the junction between the p-type and n-type materials, and each recombination event will result in the production of a quantum of energy that is an inherent feature of the semiconductor where the recombination happens.
In the semiconductor's valence band, holes are produced, whereas electrons are produced in the conduction band. The bandgap energy, which refers to the energy difference between the conduction band and the valence band, is governed by the semiconductor's bonding properties.
A single photon of light with an energy and wavelength (the two are connected to one another by Planck's equation) dictated by the bandgap of the material utilised in the active area of the device is produced via radiation recombination.
Non-radiative recombination is another possibility, when the energy generated by the electron and hole recombination results in heat instead of light photons. In direct bandgap semiconductors, these non-radiative recombination processes include mid-gap electronic states brought on by flaws.
We aim to improve the proportion of radiative recombination relative to non-radiative recombination because we want our LEDs to emit light rather than heat. To do this, one method is to add carrier-confining layers and quantum wells to the diode's active area in an effort to boost the concentration of the electrons and holes that, under the correct circumstances, are undergoing recombination.
Reduced defect concentration in the device's active area, which leads to non-radiative recombination, is another crucial factor. Because dislocations are the main source of non-radiative recombination centres, they play a crucial role in optoelectronics. Dislocations can result from a variety of factors, but in order to achieve a low density, the n- and p-type layers that make up the active area of the LED must always be grown on a lattice-matched substrate. If not, dislocations will be added to account for the variation in crystal-lattice structure.
Therefore, maximising LED performance entails reducing dislocation densities while boosting radiative recombination rate compared to non-radiative recombination rate.
LEDs UVC
Applications for ultraviolet (UV) LEDs include the treatment of water, optical data storage, communications, the detection of biological agents, and the curing of polymers. Wavelengths between 100 nm to 280 nm are referred to as the UVC portion of the UV spectrum.
The ideal wavelength for disinfection is between 260 and 270 nm, with longer wavelengths producing exponentially less germicidal efficiency. In comparison to conventional mercury lamps, UVC LEDs provide a number of advantages, including the absence of hazardous materials, instantaneous on/off switching without cycle restrictions, reduced heat consumption with focused heat extraction, and increased durability.
In the case of UVC LEDs, a greater aluminium mole percentage is necessary to generate short wavelength emission (260 nm to 270 nm for disinfection), which makes the development and doping of the material challenging. Historically, sapphire was the most widely utilised substrate for the III-nitrides since bulk lattice-matched substrates were not easily accessible. A substantial lattice mismatch between sapphire and the high-Al-content AlGaN structure of UVC LEDs causes more non-radiative recombination (defects).
The difference between the two technologies appears to be less pronounced in the UVB range and at longer wavelengths, where the lattice-mismatch with AlN is larger because higher concentrations of Ga are required. This effect seems to get worse at higher Al concentration, so sapphire-based UVC LEDs tend to drop in power at wavelengths shorter than 280 nm faster than AlN-based UVC LEDs.
Pseudomorphic growth on native AlN substrates produces atomically flat, low defect layers with a peak power at 265 nm, which corresponds to both the maximum germicidal absorption and also lessens the effects of uncertainty brought on by spectral-dependent absorption strength. This is accomplished by compressing the larger lattice parameter of intrinsic AlGaN to fit on the AlN without introducing defects.
High-quality bulk lattice-match AlN substrates have been created by BENWEI, allowing for lower internal absorption and greater internal efficiency. These substrates provide higher-quality, more potent LEDs with wavelengths in the germicidal region, which are employed in the production of Klaran UVC LEDs and goods.
