Epitaxial approach for silicon avalanche photodiode performance improvements

Previous avalanche photodiodes (APDs) studies at Radiation Monitoring Devices (RMD) have focused on increasing the slope of the p-type doping gradient in the drift region and decreasing its thickness. This work has led to significant improvements in charge collection, resulting in a higher quantum efficiency (QE), as well as noise reduction by as much as a factor of 4, resulting in an overall improvement to the APD signal-to-noise [1]. Additionally, as the drift region thickness decreases, the APD speed of response increases for those photoelectrons generated near the sensing surface of the device. Motivated by this, we have produced APDs whose 15 μm thick drift region has been replaced with ~3 μm epitaxially grown silicon layer that possesses a steep p-type dopant gradient. These epi-APDs have shown a similar response to x-rays compared to standard processed APDs operated at the same gain. The epi-APDs show a 22% increase in QE at 420 nm, high gain, faster temporal properties, however, the APD dark noise increased.