Single Photon Avalanche diodes (SPADs) were first realized more than five decades ago, and have now been industrialized for mass production in the 130 nm CMOS technology node by STMicroelectronics (STM). In this paper we present the latest STM SPAD with an excellent NIR photon detection probability (>5% at 850nm), a dark count rate median of 100 cps at room temperature and a low breakdown voltage of 14.2V. The dead time of the SPAD is approximately 25 ns, leading to a maximum count rate of 40 Mcps.
Thanks to the 130 nm gate length of the CMOS technology used and the associated high digital gate density, complex digital signal processing can be implemented allowing fully integrated systems to be realized. The low bias required by the SPAD makes it possible for voltage generation to be achieved on-chip (e.g. charge pumped).
We introduce our first generation time-of-flight system (VL6180) based on the STM SPAD technology, which is capable of ranging up to 60 cm in 60 ms. Ranging capabilities and accuracy are measured using a set of moving targets with reflectance of 5%, 17% and 88% in a fully automated test bed. To the best of our knowledge this was the first high volume SPAD-based device.
To our knowledge this is the first time details of SPAD performance over production volumes and lifetime have been presented.
Time-resolved photoluminescence decay measurements have been performed on samples with varying sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate mis-orientation alone, but otherwise under identical growth conditions. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident energy density range of 0.79 pJcm-2 - 40 nJcm-2 at a temperature of 77 K were obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident bi-exponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier re-capturing and indirect radiative recombination processes. Also experimental evidence of the effect of the AlGaAs barrier in InAs QDs emitting in the wavelength range 1200-1300nm is presented. Time-resolved photoluminescence measurements have been performed on samples with different compositions of Al in the barrier. A full discussion of the lifetimes of these near infra-red emitting dots will be presented.