Schottky Photodiode Schottky photodiodes are made of metal-semiconductor junctions. They have a simple structure, require only one photolithography step and have a thin active region and low capacitance to give a very high response speed. Carriers are generated when light enters the semiconductor and are collected by the electric field to produce a photocurrent. Schottky Photodiodes can be arranged with interdigited electrodes as shown in Figure 5 to form metal-semiconductor-metal (MSM) photodetectors. Figure : Schematic (left), top-view (right) diagrams and band diagram (bottom) of Schottky photodiode have pure drift photocurrent and no diffusion component but suffer from high dark currents from the back-to-back Schottky barrier junctions. Their low responsivity is caused by reflection from the metal contacts (although back-illumination is possible) and the finite carrier lifetime, since they have to cross the metal gaps before being collected. Photomultiplier Tubes Photomultiplier tubes (PMTs) are vacuum glass tubes with a photosensitive surface, which emits electrons when hit by photons. The electron is attracted to the focusing electrode and then multiplied by a process called secondary emission. It passes through a series of additional electrodes where each one is held at approximately 100 V higher than the previous electrode, as shown in Figure 6. Figure : Photomultiplier tube diagram The electrode stack allows for extremely high gains of up to 100 million at a reference bandwidth of 1 Hz. The bandwidth however is generally quite low. The device must be operated in total darkness to avoid over excitation and is operated at over one thousand Volts. Quantum efficiency (percentage of photons absorbed) is in the single percent range but can reach 20-40% for research-grade devices. PMTs are commonly used in physics laboratories, observatories and medical equipment.
Schottky Photodiode Schottky photodiodes are made of metal-semiconductor junctions. They have a simple structure, require only one photolithography step and have a thin active region and low capacitance to give a very high response speed. Carriers are generated when light enters the semiconductor and are collected by the electric field to produce a photocurrent. Schottky Photodiodes can be arranged with interdigited electrodes as shown in Figure 5 to form metal-semiconductor-metal (MSM) photodetectors. Figure : Schematic (left), top-view (right) diagrams and band diagram (bottom) of Schottky photodiode have pure drift photocurrent and no diffusion component but suffer from high dark currents from the back-to-back Schottky barrier junctions. Their low responsivity is caused by reflection from the metal contacts (although back-illumination is possible) and the finite carrier lifetime, since they have to cross the metal gaps before being collected. Photomultiplier Tubes Photomultiplier tubes (PMTs) are vacuum glass tubes with a photosensitive surface, which emits electrons when hit by photons. The electron is attracted to the focusing electrode and then multiplied by a process called secondary emission. It passes through a series of additional electrodes where each one is held at approximately 100 V higher than the previous electrode, as shown in Figure 6. Figure : Photomultiplier tube diagram The electrode stack allows for extremely high gains of up to 100 million at a reference bandwidth of 1 Hz. The bandwidth however is generally quite low. The device must be operated in total darkness to avoid over excitation and is operated at over one thousand Volts. Quantum efficiency (percentage of photons absorbed) is in the single percent range but can reach 20-40% for research-grade devices. PMTs are commonly used in physics laboratories, observatories and medical equipment.
CORRECTED%20Max%20Rowe%20-%20MPhil%20Thesis.docx