We performed a systematic study involving simulation and experimental techniques to develop induced-junction silicon photodetectors passivated with thermally grown SiO₂ and plasma-enhanced chemical vapor deposited (PECVD) SiN_x thin films that show a record high quantum efficiency. We investigated PECVD SiN_x passivation and optimized the film deposition conditions to minimize the recombination losses at the silicon–dielectric interface as well as optical losses. Depositions with varied process parameters were carried out on test samples, followed by measurements of minority carrier lifetime, fixed charge density, and optical absorbance and reflectance. Subsequently, the surface recombination velocity, which is the limiting factor for internal quantum deficiency (IQD), was obtained for different film depositions via 2D simulations where the measured effective lifetime, fixed charge density, and substrate parameters were used as input. The quantum deficiency of induced-junction photodiodes that would be fabricated with a surface passivation of given characteristics was then estimated using improved 3D simulation models. A batch of induced-junction photodiodes was fabricated based on the passivation optimizations performed on test samples and predictions of simulations. Photodiodes passivated with PECVD SiN_x film as well as with a stack of thermally grown SiO₂ and PECVD SiN_x films were fabricated. The photodiodes were assembled as light-trap detector with 7-reflections and their efficiency was tested with respect to a reference Predictable Quantum Efficient Detector (PQED) of known external quantum deficiency. The preliminary measurement results show that PQEDs based on our improved photodiodes passivated with stack of SiO₂/SiN_x have negligible quantum deficiencies with IQDs down to 1 ppm within 30 ppm measurement uncertainty.

We determine experimentally the internal quantum efficiency of a 3-element trap detector made of Hamamatsu S1337 photodiodes and of a predictable quantum efficient detector (PQED) over the wavelength range of 250–500 nm using an electrically calibrated pyroelectric radiometer as reference detector. The PQED is made of specially designed induced junction photodiodes, whose charge-carrier recombination losses are minimized. The determined internal quantum efficiency of PQED is always 1 or larger, whereas the 3-element trap detector has internal quantum efficiency smaller than 1 in the spectral range of 330–450 nm. This finding demonstrates the advantages of PQED photodiodes for studying the quantum yield due to impact ionization by charge carriers in the silicon lattice. For this purpose, we develop an extrapolation model for the charge-carrier recombination losses of the PQED, which allows us to separate the quantum yield from the measured internal quantum efficiency. Measurements of PQED spectral responsivity thus allow to determine the quantum yield in silicon, which can be further used for quantifying the charge-carrier recombination losses in the 3-element trap detector. Numerical values of the latter are from 6% to 2% in the spectral range from 250 nm to 380 nm. Finally, our results are encouraging for the aim of developing the PQED to a primary detector standard also at ultraviolet wavelengths.

Photons absorbed in silicon produce electron–hole pairs, which can cause impact ionization and quantum yield larger than one. Reliable determination of quantum yield at low charge-carrier energies (<4 eV) has been challenging because photon losses due to reflectance and charge-carrier losses due to recombination affect the resulting photocurrent. Here, we present how the measurement of this fundamental characteristic of silicon crystals can be improved in the charge-carrier energy range of 1.6–4 eV by using a predictable quantum efficient detector based on induced junction photodiodes optimized for photon-to-electron conversion efficiency. The measured quantum yield values are compared with the results of theoretical calculations, revealing increased impact-ionization probabilities at 2.25 and 3.23 eV on the top of a smooth background curve calculated by a model based on free charge carriers in the silicon lattice. For the results at the lowest energies, both data and an asymptotic extrapolation model suggest that quantum yield exceeds unity by ∼10−4 at 1.6 eV corresponding to a photon wavelength of 450 nm.

We investigate the predictable quantum efficient detector (PQED) in the visible and near-infrared wavelength range. The PQED consists of two n-type induced junction photodiodes with Al₂O₃ entrance window. Measurements are performed at the wavelengths of 488 nm and 785 nm with incident power levels ranging from 100 µW to 1000 µW. A new way of presenting the normalized photocurrents on a logarithmic scale as a function of bias voltage reveals two distinct negative slope regions and allows direct comparison of charge carrier losses at different wavelengths. The comparison indicates mechanisms that can be understood on the basis of different penetration depths at different wavelengths (0.77 μm at 488 nm and 10.2 μm at 785 nm). The difference in the penetration depths leads also to larger difference in the charge-carrier losses at low bias voltages than at high voltages due to the voltage dependence of the depletion region.

The Predictable Quantum Efficient Detector (PQED) is a silicon-based optical sensor which is designed to convert every photon in the incident photon flux to an electron–hole pair