Changes

The standard technology for such detectors, originally developed for atomic and nuclear physics experiments, is based on the photomultiplier vacuum tube.  Particle physics experiments have relied on photomultiplier tubes for over 40 years.  Ever since the invention of the transistor, efforts have been made to create semiconductor-based photon detectors, but certain drawbacks have limited their use to a few niche applications.  Recently, however, progress has been made toward the goal of creating silicon-based detectors with single-photon sensitivity that can operate at room temperature.  These devices are called silicon photomultipliers.

The standard technology for such detectors, originally developed for atomic and nuclear physics experiments, is based on the photomultiplier vacuum tube.  Particle physics experiments have relied on photomultiplier tubes for over 40 years.  Ever since the invention of the transistor, efforts have been made to create semiconductor-based photon detectors, but certain drawbacks have limited their use to a few niche applications.  Recently, however, progress has been made toward the goal of creating silicon-based detectors with single-photon sensitivity that can operate at room temperature.  These devices are called silicon photomultipliers.

Silicon photomultipliers use semiconducting technology to detect single photons at room temperature. Semiconductors are solids that have a conductivity between that of conductors and insulators. (Electrical conductivity is the ability for a substance to move electrons from one area to another. It is primarily determind by the band gap of a substance. The band gap is the distance that an electron must travel before it goes into the conduction band. Smaller band gaps would equal a higher electrical conductivity)  

Silicon photomultipliers use semiconducting technology to detect single photons at room temperature. Semiconductors are solids that have a conductivity between that of conductors and insulators, and can be changed with the addition of different impurities. (Electrical conductivity is the ability for a substance to move electrons from one area to another. It is primarily determind by the band gap of a substance. The band gap is the distance that an electron must travel before it goes into the conduction band. Smaller band gaps would equal a higher electrical conductivity) Semiconductors can be used to detect single photons because of their sensitivity to electrical fields. If a photon were to hit a semiconductor, it would produce an electron ... (why can't conductors be used instead of an semiconductor, wouldn't their sensitivities be higher because they have a smaller band gap?)

(need a sentence that introduces the basic physics of how semiconductors can work as photon detectors.)

The vast majority of electrical devices today make use of semiconductors. One very common electrical component is called a diode. A diode is a device that allows electricity to flow one way, but not the other.

A normal diode is a device that allows electricity to flow one way, but not the other. It is used in a lot of very common electrical appliances, from computers to toasters. Photodiodes produce a single electron from each photon that hits the detector area. But since physicists are trying to detect single photons, that is not nearly enough. They had to create a device that releases many electrons for every single photon that hits the detector. (Discussion on PMT?) They could do just that with the avalanche photodiode. Diodes only allow electricity to flow one way. So if voltage is applied in the opposite direction of the way that the electrons were meant to flow, no electricity would cross. Yet every single diode has a breaking point. If enough voltage, or electrical force, is put across a diode, it could suddenly allow all the electricity through, like a dam breaking. The voltage that is applied in the reverse direction is called reverse bias voltage. Physicists take advantage of that effect by applying enough reverse bias voltage that the Avalanche photodiode that anything, even the energy from a single photon is sufficient to cause it to break down. This is called the breakdown voltage. If a photon were to hit this diode, it would cause a huge surge of electricity to go through the diode and therefore the entire curcuit, one that could be measured by the scientist.  

Photodiodes produce a single electron from each photon that hits the detector area. But since physicists are trying to detect single photons, that is not nearly enough. They had to create a device that releases many electrons for every single photon that hits the detector. (Discussion on PMT?) They could do just that with the avalanche photodiode. Diodes only allow electricity to flow one way. So if voltage is applied in the opposite direction of the way that the electrons were meant to flow, no electricity would cross. Yet every single diode has a breaking point. If enough voltage, or electrical force, is put across a diode, it could suddenly allow all the electricity through, like a dam breaking. The voltage that is applied in the reverse direction is called reverse bias voltage. Physicists take advantage of that effect by applying enough reverse bias voltage that the Avalanche photodiode that anything, even the energy from a single photon is sufficient to cause it to break down. This is called the breakdown voltage. If a photon were to hit this diode, it would cause a huge surge of electricity to go through the diode and therefore the entire curcuit, one that could be measured by the scientist.  

Normally, when a diode breaks down, it allows all the electricity to go through, causing it to heat up immediatly and burn up in an instant. But in the interests of preserving the photodiode for reuse, a resister is introduced in the circuit. This resister limits the amount of aperage, or the number of electrons from going through the circuit, and therefore prevents the photodiode from burning up.  

Normally, when a diode breaks down, it allows all the electricity to go through, causing it to heat up immediatly and burn up in an instant. But in the interests of preserving the photodiode for reuse, a resister is introduced in the circuit. This resister limits the amount of aperage, or the number of electrons from going through the circuit, and therefore prevents the photodiode from burning up.