Impact of defects on the spectral characteristics of PureB avalanche-mode light emitting diodes

Single photon avalanche diodes (SPADs) fabricated in PureB silicon technology offer exceptional versatility, functioning both as light emitting diodes and detectors sensitive down to a single photon. In PureB technology, nanometer-thin layers of boron are deposited on the silicon surface, creating defect-free ultra-shallow junctions. In this paper, PureB diodes with a junction depth of a few tens of nanometers are studied as avalanche-mode light-emitting diodes (AMLEDs) with the advantage that optical absorption was minimal. They were systematically analyzed to investigate the impact of defects on their optical and electrical characteristics. Bulk defects were unintentionally introduced by contamination during the processing of the n⁺ buried layer. These defects cause the increase in dark currents and the formation of light-emitting spots, observable in light emission spectra taken at reverse biases below the breakdown voltage. An increase in relative intensity for wavelengths from 450 nm to 550 nm was observed in spectral characteristics of light emitting spots compared to the light emission of the active-region breakdown. Optical and electrical characterization was conducted on diodes with different geometry, implantation doses in the multiplication region, and distance to an implicit guard ring to examine the impact of these parameters on the light emission spectrum. Low-temperature electrical characteristics and light emission patterns of the devices were obtained by measurements at cryogenic temperatures.