The first optical spectroscopic investigation of MoC has revealed a complicated vibronic spectrum consisting of about 35 bands between 17 700 and 24 000 cm−1. Analysis has shown the ground state to be the Ω=0+ spinorbit component of a Σ3− state that derives from a 10σ211σ25π42δ2 configuration. The X 3Σ0+− rotational constant for Mo9812C was determined to be B0=0.553 640±0.000 055 cm−1, giving r0=1.687 719±0.000 084 Å. Consideration of spin-uncoupling effects in the X 3Σ− state requires that this value be revised to r0=1.6760 Å, which represents our best estimate of the true Mo–C bond length. Spectroscopic constants were also extracted for six other major isotopic modifications of MoC in this mass resolved experiment. All rotationally resolved transitions were found to originate from the ground state and terminate in electronic states with Ω=1. An attempt is made to classify the observed transitions into band systems, to rationalize the complexity of the spectrum, and to understand the bonding from a molecular orbital point of view.
We report on the demonstration of Al0.85Ga0.15As0.56Sb0.44 (hereafter, AlGaAsSb) avalanche photodiodes (APDs) with a 1000 nm-thick multiplication layer. Such a thick AlGaAsSb device was grown by a digital alloy technique to avoid phase separation. The current-voltage measurements under dark and illumination conditions were performed to determine gain for the AlGaAsSb APDs. The highest gain was ∼ 42, and the avalanche initiation occurred at 21.6 V. The breakdown voltage was found to be around −53 V. The measured dark current densities of bulk and surface components were 6.0 μA/cm2 and 0.23 μA/cm, respectively. These values are about two orders of magnitude lower than those for previously reported 1550 nm-thick AlAs0.56Sb0.44 APDs [Yi et al., Nat. Photonics 13, 683 (2019)]. Excess noise measurements showed that the AlGaAsSb APD has a low k of 0.01 (the ratio of electron and hole impact ionization coefficients) compared to Si APDs. The k of the 1000-nm AlGaAsSb APD is similar to that of the thick AlAsSb APDs (k ∼ 0.005) and 5–8 times lower than that of 170 nm-thick AlGaAsSb APDs (k ∼ 0.5–0.8). Increasing the thickness of the multiplication layer over 1000 nm can also reduce k further since the difference between electron and hole impact ionization coefficients becomes significant in this material system as the thickness of the multiplication layer increases. Therefore, this thick AlGaAsSb-based APD on an InP substrate shows the potential to be a high-performance multiplier that can be used with available short-wavelength infrared (SWIR) absorption layers for a SWIR APD.
High sensitivity avalanche photodiodes (APDs) operating at eye-safe infrared wavelengths (1400–1650 nm) are essential components in many communications and sensing systems. We report the demonstration of a room temperature, ultrahigh gain ( M = 278 , λ = 1550 n m , V = 69.5 V , T = 296 K ) linear mode APD on an InP substrate using a G a A s 0.5 S b 0.5 / A l 0.85 G a 0.15 A s 0.56 S b 0.44 separate absorption, charge, and multiplication (SACM) heterostructure. This represents ∼ 10 × gain improvement ( M = 278 ) over commercial, state-of-the-art InGaAs/InP-based APDs ( M ∼ 30 ) operating at 1550 nm. The excess noise factor is extremely low ( F <2005
We have measured the helium induced pressure broadening and shifting of the distinct hyperfine components of the j = 1 <-- 0 and j = 2 <-- 1 transitions of HC14N at temperatures between 1.3 and 20 K. The HCN molecules were cooled to these temperatures using the collisional cooling technique. As a test of this cooling technique we measured the Doppler contribution to the spectral lines, and these measurements confirm that the molecules are at the same temperature as the walls of the spectroscopic cell. We observed that the hyperfine components of the 2 <-- 1 transition have distinct broadening coefficients that differ from one another by as much as 5%. The measured differences are in reasonable agreement with theoretical predictions. We have also performed molecular scattering calculations on three He-HCN potential energy surfaces in order to compare our results with theoretical expectations. At the lowest temperatures these calculations predict broadening coefficients that are considerably larger than the measured coefficients. We have previously found a similar discrepancy for two other molecules at these low temperatures, and we discuss possible experimental and theoretical origins for this persistent discrepancy.
We report the gain, noise, and dark current characteristics of random alloy Al0.79In0.21As0.74Sb0.26 (hereafter AlInAsSb)-based avalanche photodiodes (APDs) on InP substrates. We observe, at room temperature, a low excess noise corresponding to a k value (ratio of impact ionization coefficients) of 0.018 and a dark current density of 82 μA/cm2 with a gain of 15. These performance metrics represent an order of magnitude improvement of the k-value over commercially available APDs with InAlAs and InP multiplication layers grown on InP substrates. This material is also competitive with a recently reported low noise AlAsSb on InP [Yi et al., Nat. Photonics 13, 683 (2019)], with a comparable excess noise and a room temperature dark current density almost three orders of magnitude lower at the same gain. The low excess noise and dark current of AlInAsSb make it a candidate multiplication layer for integration into a separate absorption, charge, and multiplication layer avalanche photodiode for visible to short-wavelength infrared applications.
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