Abstract

We have developed avalanche photodiode (APD) arrays of the beveled edge type with high responsivity in the ultraviolet (UV) region. A 3 × 3 array with pixel size 3 × 3 mm2 was made, in which the segmentation was done using selective diffusion in the front surface. This technique is an improvement over previous avalanche photodiodes, where the segmentation was done by cutting channels in the back of the detector. After the die was cut from the wafer, beveling and passivation was performed to avoid lateral surface breakdown. The quantum efficiency from 200 to 400 nm is close to 50%, which makes this detector suitable for Nuclear Spectroscopy applications using short wavelength scintillators. The gain and dark current coming from all pixels connected together, is similar to a single element detector with the same area, which indicates that the pixelization process does not reduce the performance compared to a detector without segmentation. We measured high crosstalk between adjacent pixels (20%) which indicates that the resistance between them is too low. Due to the high resistance, the noise in the pixels is also high, and the energy resolution from a 57Co source is higher (36% FWHM) than previous arrays.