Talha's Physics Academy
Functions and Uses of LEDs, Photodiodes, and Photovoltaic Cells
Video Lecture
Watch the complete video lecture below to understand the functions and applications of LEDs, photodiodes, and photovoltaic cells.
1. Light Emitting Diodes (LEDs)
In this process, electrons move from the negative side to the positive side, combining with holes and emitting a photon with energy similar to the material's band gap. Silicon diodes do not work well for this purpose, but compound semiconductors like gallium and arsenic create efficient LEDs. Gallium arsenide ($\text{GaAs}$), which has a crystal structure similar to silicon, is frequently used.
Applications of LEDs
LED bulbs replace traditional lighting in various applications, such as:
- Flashlights and streetlights
- Traffic signals and car brake lights
- Billboards and LCD screens
2. Photodiodes
A photodiode is a type of light detector that converts light into current or voltage. It includes optical filters, built-in lenses, and active surface areas. Photodiodes are often operated in reverse bias, where an external voltage encourages the flow of photocurrent and maximizes sensitivity.
These detectors are typically made of semiconductor materials like silicon, which can absorb photons of light. When light particles (photons) strike the semiconductor material, they transfer energy to electrons, creating electron-hole pairs. This process generates an electric current proportional to the incident light's intensity.
Applications of Photodiodes
- Optical Communication: Photodiodes are employed in optical communication systems, such as fiber optics, to detect and convert transmitted light signals into electrical signals.
- Light Sensors: They are used in electronic devices like cameras, light meters, and automatic lighting systems to sense ambient light levels.
- Barcode Readers: Photodiodes are frequently used in barcode scanners to detect reflected light from barcodes.
- Medical Devices: In various medical instruments, photodiodes are utilized for tasks such as measuring oxygen levels in the blood.
3. Photovoltaic Cell
A photovoltaic cell is a heavily doped p-n junction diode used to convert sunlight directly into electrical energy. If the energy of an incident photon is greater than the material's band gap energy, it creates electron-hole pairs.
The absorbed photon excites an electron from the valence band and produces a current when connected to an external circuit, functioning as a source of electromotive force (emf) and power.
The basic building block of a photovoltaic cell is a semiconductor material, usually silicon, chosen for its widespread availability. Other semiconductor materials, such as cadmium telluride or copper indium gallium selenide, are also used in specialized types of solar cells.
A typical silicon p-n junction produces about $0.6\text{ V}$. Many such cells are connected in series to produce higher voltages. These series strings are then connected in parallel within a photovoltaic panel (solar panel). A high-efficiency photovoltaic panel can have an output of approximately $50\text{ W/m}^2$, averaged over day and night, sunny and cloudy conditions.
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