Correction: Jegannathan et al. An Overview of CMOS Photodetectors Utilizing Current-Assistance for Swift and Efficient Photo-Carrier Detection. Sensors 2021, 21, 4576.

There was an error in the original publication, in Equation (5) [...].

An Overview of CMOS Photodetectors Utilizing Current-Assistance for Swift and Efficient Photo-Carrier Detection.

This review paper presents an assortment of research on a family of photodetectors which use the same base mechanism, current assistance, for the operation. Current assistance is used to create a drift field in the semiconductor, more specifically silicon, in order to improve the bandwidth and the quantum efficiency. Based on the detector and application, the drift field can be static or modulated. Applications include 3D imaging (both direct and indirect time-of-flight), optical receivers and fluorescence lifetime imaging. This work discusses the current-assistance principle, the various photodetectors using this principle and a comparison is made with other state-of-the-art photodetectors used for the same application.

Synthesis and Characterization of Double Solid Solution (Zr,Ti)2(Al,Sn)C MAX Phase Ceramics.

Quasi phase-pure (>98 wt %) MAX phase solid solution ceramics with the (Zr,Ti)2(Al0.5,Sn0.5)C stoichiometry and variable Zr/Ti ratios were synthesized by both reactive hot pressing and pressureless sintering of ZrH2, TiH2, Al, Sn, and C powder mixtures. The influence of the different processing parameters, such as applied pressure and sintering atmosphere, on phase purity and microstructure of the produced ceramics was investigated. The addition of Sn to the (Zr,Ti)2AlC system was the key to achieve phase purity. Its effect on the crystal structure of a 211-type MAX phase was assessed by calculating the distortions of the octahedral M6C and trigonal M6A prisms due to steric effects. The M6A prismatic distortion values were found to be smaller in Sn-containing double solid solutions than in the (Zr,Ti)2AlC MAX phases. The coefficients of thermal expansion along the ⟨ a⟩ and ⟨ c⟩ directions were measured by means of Rietveld refinement of high-temperature synchrotron X-ray diffraction data of (Zr1- x,Ti x)2(Al0.5,Sn0.5)C MAX phase solid solutions with x = 0, 0.3, 0.7, and 1. The thermal expansion coefficient data of the Ti2(Al0.5,Sn0.5)C solid solution were compared with those of the Ti2AlC and Ti2SnC ternary compounds. The thermal expansion anisotropy increased in the (Zr,Ti)2(Al0.5,Sn0.5)C double solid solution MAX phases as compared to the Zr2(Al0.5,Sn0.5)C and Ti2(Al0.5,Sn0.5)C end-members.

The double solid solution (Zr, Nb)2(Al, Sn)C MAX phase: a steric stability approach.

The addition of Nb and Sn to Zr2AlC is investigated, targeting the synthesis of a Zr-rich bulk MAX phase free of ZrC. The 211 phase formation in the two quaternary Zr-Nb-Al-C and Zr-Al-Sn-C systems is evaluated. Solubility over the entire compositional range in (Zr, Nb)2AlC and Zr2(Al, Sn)C is observed. In terms of effectiveness, the addition of Sn is preferred over the addition of Nb, as the former is selectively incorporated into the 211 structure. A combinatorial approach results in the formation of phase-pure (Zr0.8, Nb0.2)2(Al0.5, Sn0.5)C. The effect of the added solutes on the microstructure and crystallographic parameters is investigated. The addition of Nb and Sn reduces the distortion parameter of the trigonal prism compared to pure Zr2AlC. Therefore, an attempt is made to establish a more general stability criterion for the M2AC structure based on the steric relationship between the atoms in the M6A trigonal prism. Inspired by the Hume-Rothery rules, it is suggested that comparable atomic radii of the M- and A-atoms provide a good starting point to obtain a stable 211 MAX phase.

Theoretical Prediction and Synthesis of (Cr2/3Zr1/3)2AlC i-MAX Phase.

Guided by predictive theory, a new compound with chemical composition (Cr2/3Zr1/3)2AlC was synthesized by hot pressing of Cr, ZrH2, Al, and C mixtures at 1300 °C. The crystal structure is monoclinic of space group C2/ c and displays in-plane chemical order in the metal layers, a so-called i-MAX phase. Quantitative chemical composition analyses confirmed that the primary phase had a (Cr2/3Zr1/3)2AlC stoichiometry, with secondary Cr2AlC, AlZrC2, and ZrC phases and a small amount of Al-Cr intermetallics. A theoretical evaluation of the (Cr2/3Zr1/3)2AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (Cr2/3Hf1/3)2AlC, of the same structure, was predicted to be stable.

Synthesis of MAX Phases in the Zr-Ti-Al-C System.

This study reports on the synthesis and characterization of MAX phases in the (Zr,Ti)n+1AlCn system. The MAX phases were synthesized by reactive hot pressing and pressureless sintering in the 1350-1700 °C temperature range. The produced ceramics contained large fractions of 211 and 312 (n = 1, 2) MAX phases, while strong evidence of a 413 (n = 3) stacking was found. Moreover, (Zr,Ti)C, ZrAl2, ZrAl3, and Zr2Al3 were present as secondary phases. In general, the lattice parameters of the hexagonal 211 and 312 phases followed Vegard's law over the complete Zr-Ti solid solution range, but the 312 phase showed a non-negligible deviation from Vegard's law around the (Zr0.33,Ti0.67)3Al1.2C1.6 stoichiometry. High-resolution scanning transmission electron microscopy combined with X-ray diffraction demonstrated ordering of the Zr and Ti atoms in the 312 phase, whereby Zr atoms occupied preferentially the central position in the close-packed M6X octahedral layers. The same ordering was also observed in 413 stackings present within the 312 phase. The decomposition of the secondary (Zr,Ti)C phase was attributed to the miscibility gap in the ZrC-TiC system.

Synthesis of MAX Phases in the Hf-Al-C System.

For the first time, MAX phases in the Hf-Al-C system were experimentally synthesized using reactive hot pressing. HfC was observed as the main competing phase. The lattice parameters of Hf2AlC and Hf3AlC2 were determined by Rietveld refinement based on the X-ray diffraction data. The atomic stacking sequence was revealed by high-resolution scanning transmission electron microscopy. Mixtures of 211 and 312 stacking were observed within the same grain, including 523 layers. This transition in atomic structure is discussed.

(Nbx, Zr1-x)4AlC3 MAX Phase Solid Solutions: Processing, Mechanical Properties, and Density Functional Theory Calculations.

The solubility of zirconium (Zr) in the Nb4AlC3 host lattice was investigated by combining the experimental synthesis of (Nbx, Zr1-x)4AlC3 solid solutions with density functional theory calculations. High-purity solid solutions were prepared by reactive hot pressing of NbH0.89, ZrH2, Al, and C starting powder mixtures. The crystal structure of the produced solid solutions was determined using X-ray and neutron diffraction. The limited Zr solubility (maximum of 18.5% of the Nb content in the host lattice) in Nb4AlC3 observed experimentally is consistent with the calculated minimum in the energy of mixing. The lattice parameters and microstructure were evaluated over the entire solubility range, while the chemical composition of (Nb0.85, Zr0.15)4AlC3 was mapped using atom probe tomography. The hardness, Young's modulus, and fracture toughness at room temperature as well as the high-temperature flexural strength and E-modulus of (Nb0.85, Zr0.15)4AlC3 were investigated and compared to those of pure Nb4AlC3. Quite remarkably, an appreciable increase in fracture toughness was observed from 6.6 ± 0.1 MPa/m(1/2) for pure Nb4AlC3 to 10.1 ± 0.3 MPa/m(1/2) for the (Nb0.85, Zr0.15)4AlC3 solid solution.