International Radiation Detectors, Inc.

Operating Principles

When the diode is exposed to photons of energy greater than 1.12 eV (wavelength less than 1100 nm), electron-hole pairs (carriers) are created. These photogenerated carriers are separated by the p-n junction electric field and a current proportional to the number of electron-hole pairs created flows through an external circuit. Ultraviolet photons, with wavelength shorter than about 350 nm, create more than one electron-hole pair [1]. This results in internal quantum efficiencies greater than unity as shown in Figure 1.

Fig. 1: Internal quantum efficiency of UVG photodiodes

Two unique properties of the UVG photodiodes have resulted in previously unattained stable and 100% collection efficiencies and near theoretical quantum efficiencies.

The first property is the absence of a surface dead region i.e. no photogenerated carrier recombination occurs in the doped n-type region and at the silicon-silicon dioxide interface. As the absorption depths for the majority of UV photons are less than 1 micrometer in silicon, the absence of a dead region yields complete collection of photogenerated carriers by an external circuit resulting into 100% collection efficiency. The flat region from 310 nm to 640 nm in Figure 1 shows that these diodes have 100% collection efficiency.

References:

1] R. Korde and J. Geist, "Quantum Efficiency Stability of Silicon Photodiodes"

Applied Optics, Vol. 26, 5284-5290 (1987).