What is a Photodiode?

A photodiode (PD) is a semiconductor naphthalene semiconductor that functions as an electronic switch. Herein, a series of silicon (NWs) nanowires (Nws) are shown to display excellent photodiode performance both at room temperature and when exposed to visible light. These devices also exhibit tunability in the number of nanowires that can be contained within the same device, and so can be used as opto-transparent devices with photo-discharge tolerance up to -40% of the voltage. A PD device is an inexpensive way to build a solar panel, since solar energy conversion efficiency is directly proportional to the square of the area enclosed by the device, and for this reason many solar panels can fit neatly onto a single PD. The photodiode devices shown here are fabricated using a highly effective method called ionic vented deposition.

A photodiode consists of a semiconductor material like silicon, gallium arsenide, indium arsenide, or even lithium phosphate. When electricity is passed through silicon, it causes the electron to be knocked loose. This mobility is very important in nanotechnology, because instead of having to trap an electron, one can simply "leak" it out, resulting in the generation of free radicals, which in turn damage the electronics. However, when an electrical current is passed through silicon, the charge carriers become trapped inside the semiconductor lattice, resulting in an overall increase in the amount of available charge carriers. Thus by coupling the electronic properties with the electrical charges, nanotechnology researchers have developed a way of improving the charge carrier mobility, thus increasing efficiency.

Photovoltaic nanothermics are based on nanotechnology principles and have been around for decades. The concept behind the device has changed drastically in recent years. Originally, the photodiode was a solid-state device made of a solid silicon semiconductor that was charged by applying direct current to the surface. However, this method of producing a photodiode was rather inefficient and not very efficient.

The surface of the device would absorb all of the light that shone on it. As the current passed through the photodiode, however, most of the light energy would be absorbed as heat, rather than being converted into usable electricity. As more research efforts continued to improve the efficiency of photodiodes, the surface of the device itself was developed to allow only a certain portion of the light to pass through. The portion that did make it through would be nearly all energy in the form of infrared light.

Today's most commonly used photodiodes are composed of two substances, typically silicon dioxide and phosphorophane. Silicon dioxide is a solution of pure silicon and a number of elements that have the properties necessary for the generation of electricity. Phosphorophane is a combination of phosphoric acid and silicon dioxide, with each serving a different purpose. The phosphoric acid serves a useful role in the generation of energy from light, while the silicon dioxide absorbs the sun's light and then passes on this energy to an electrode.

With the addition of silicon dioxide, which acts as a source of electrons, the efficiency of the photodiode increases greatly. While silicon dioxide is an extremely effective conductor of electricity, however, it is still only effective if the electrical current is applied to a surface with a large surface area, such as the photodiode used in calculators or television screens. This is why many photodiodes are placed inside of devices where they cannot be seen.

Photodiodes are used in many different ways in modern technology. Some devices, such as digital cameras and cell phones, rely on the ability of the photodiode to absorb a large amount of light. By using a combination of LED light emitting diodes and photoelectric cells, many digital cameras can take beautiful pictures even in poor lighting conditions. Cell phones, on the other hand, use photodiode inside the unit to both detect movement and to automatically light up the phone when it is switched on. In these devices, the photodiode help to keep the electronic components within the unit lit, while keeping the electricity flowing. This functionality makes them particularly useful in medical imaging applications, where light is often vital to properly diagnose a patient.

Another way in which many modern devices make use of photodiodes is in the production of infrared light. This light, which has the same wavelength as natural sunlight, can pass through many surfaces without being absorbed. Because many devices generate this light, photodiode inside of the device may not even be visible. By placing a photodiode array, or photodiode behind a lens in a camera for instance, light from the device can be filtered through the silicon dioxide so that the light can be seen.