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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 semiconductor technology to detect single photons at room temperature. A semiconductor is a material with an electrical conductivity between that of a conductor and an insulator. The electrical conductivity of a substance measures how much electric current flows when a given electrical potential is placed across it. A perfect insulator has an electrical conductivity of 0, indicating that no current flows through it even when an electrical difference is present. A semiconductor normally acts like an insulator up to certain potential difference, called the breakdown voltage, above which it becomes conducting. The vast majority of electrical devices today make use of semiconductors. One very common electrical component of semiconductor electroics is the diode. A diode is like a valve for electric current, that conducts current in one direction, but not the other. (See Image 1 for more information) [[Image:Diode_Plot.jpg|thumb|250px|Image 1: Diode Diagram]]As with any electrical device, when the electrical potential is 0, there is no current flowing, But even at very small electrical potentials in the forward direction, no current flows in a diode. A diode only begins to act like a conductor once it reaches a cutoff voltage(<math>V_{Cut}</math>). Upon reaching that cutoff voltage, the semiconductor begins to act like a conductor, causing the amount of current to increase very quickly. When an electrical potential is placed across a diode in the reverse direction, the diode prevents all current to flow until a certain breakdown voltage. At that breakdown voltage, the diode is no longer able to hold back the electrical potential and spontaneously breaks down, becoming a conductor, no longer resisting current flow. This results in a sharp spike of current in the reverse direction.  

Silicon photomultipliers use semiconductor technology to detect single photons at room temperature. A semiconductor is a material with an electrical conductivity between that of a conductor and an insulator. The electrical conductivity of a substance measures how much electric current flows when a given electrical potential is placed across it. A perfect insulator has an electrical conductivity of 0, indicating that no current flows through it even when an electrical difference is present. A semiconductor normally acts like an insulator up to certain potential difference, called the breakdown voltage, above which it becomes conducting. The vast majority of electrical devices today make use of semiconductors. One very common electrical component of semiconductor electroics is the diode. A diode is like a valve for electric current, that conducts current in one direction, but not the other. (See Image 1 for more information) [[Image:Diode_Plot.jpg|thumb|250px|Image 1: Diode Diagram]]As with any electrical device, when the electrical potential is 0, there is no current flowing, But even at very small electrical potentials in the forward direction, no current flows in a diode. A diode only begins to act like a conductor once it reaches a cutoff voltage(<math>V_{Cut}</math>). Upon reaching that cutoff voltage, the semiconductor begins to act like a conductor, causing the amount of current to increase very quickly. When an electrical potential is placed across a diode in the reverse direction, the diode prevents all current to flow until a certain breakdown voltage. At that breakdown voltage, the diode is no longer able to hold back the electrical potential and spontaneously breaks down, becoming a conductor, no longer resisting current flow. This results in a sharp spike of current in the reverse direction. The breakdown voltage is much larger than the cutoff voltage