| 摘要 |
A photon detection system comprising an avalanche photo-diode APD , comprising a p-n junction formed from a first semiconductor layer 103,105 having a first conductivity type and a second semiconductor layer 107 having a second conductivity type, wherein the first conductivity type is one selected from n-type or p-type and the second conductivity type is different to the first conductivity type and is selected from n type or p-type, wherein the first semiconductor layer is a doped layer which is doped with dopants of a first conductivity type and where there is a variation in the concentration of dopants of the first conductivity type such that the first layer comprises islands 105 of high field zones surrounded by low field zones , the high and low field zones distributed laterally in the plane of the p-n junction, wherein the dopant concentration is higher in the high field zones than the low field zones. The second layer abuts the first layer to form a p-n junction with both high and low field zones in the first layer. The high field zones have a geometric filling factor of 0.5 or more. The system further comprising a biasing unit, (figure 3, 6) said biasing unit being configured to apply an AC and DC voltage across the p-n junction. The system further comprises a counting circuit, a discriminator and a band rejection filter 337 for measuring an avalanche event, and whereby the detection system is capable of removing a time varying component from the output signal of the APD. Preferably the biasing circuit is configured to apply a time varying component (figure 4) to be above the breakdown voltage of the APD, but is of short duration to prevent the avalanche current saturating the whole device. The system also includes a lens and collimating optics to disperse light uniformly across the avalanche photo diode. |
