Thin AlGaAsSb Avalanche Photodiodes with Low Excess Noise

In photon-starved or high-speed applications, such as optical communications or medical imaging, where detection of weak light signals is required, avalanche photodiodes (APDs) are widely used. APDs with thin avalanche regions have shown low excess noise characteristics and high gain-bandwidth products. In this work, gain and excess noise of thin Al0.85Ga0.15As0.56Sb0.44 (lattice-matched to InP substrates) p-i-n and n-i-p diodes with 100 and 200 nm avalanche regions have been measured for different carrier injection conditions. Very low excess noise values were obtained in p-i-n devices under pure electron injection, with effective ionisation ratios keff = 0.08-1. The AlGaAsSb electron ionisation coefficient was found to be higher than the hole ionisation coefficient�. A significant dead-space effect has been observed in such thin layers, reducing the excess noise. Recurrence equations were used to extract the ionisation coefficients and ionisation threshold energies for the electrons and holes in AlGaAsSb. In addition, simulations using recurrence equations were carried out to simulate gain and excess noise characteristics in p-i-n diodes with keff = 0.1, 0.01, and 0.001, for different light injection profiles. F(M) characteristics were found to be higher for mixed injection conditions than for pure electron injection. However, for extremely low keff materials, excess noise remains low up to large gain values even for the most severe cases of mixed injection. Randomly-generated ionisation path lengths (RPL) simulations were also carried out to track the carriers initiating impact ionisation, and the sharp increase in F(M) characteristics was attributed to an increase in the number of hole-initiated ionisation events. Signal-to-noise (SNR) and noise-equivalent power (NEP) were calculated for APDs with keff = 0.1, 0.01, and 0.001, highlighting the interest of using avalanche gain to increase the sensitivity of optical detectors. Finally, a Separate Absorption and Multiplication (SAM) APD combining a 100 nm-thin AlGaAsSb avalanche region and a 1 um InGaAs absorption region has been studied. Low dark currents and good photoresponse at 1550 nm wavelength have been demonstrated. The temperature dependence of gain was investigated for temperatures between 77 K and room temperature, and a temperature coefficient of breakdown voltage, Cbd, of -49 mV/K was obtained

Strong interfacial exchange field in the graphene/EuS heterostructure

Exploiting 2D materials for spintronic applications can potentially realize next-generation devices featuring low-power consumption and quantum operation capability. The magnetic exchange field (MEF) induced by an adjacent magnetic insulator enables efficient control of local spin generation and spin modulation in 2D devices without compromising the delicate material structures. Using graphene as a prototypical 2D system, we demonstrate that its coupling to the model magnetic insulator (EuS) produces a substantial MEF (> 14 T) with potential to reach hundreds of Tesla, which leads to orders-of-magnitude enhancement in the spin signal originated from Zeeman spin-Hall effect. Furthermore, the new ferromagnetic ground state of Dirac electrons resulting from the strong MEF may give rise to quantized spin-polarized edge transport. The MEF effect shown in our graphene/EuS devices therefore provides a key functionality for future spin logic and memory devices based on emerging 2D materials in classical and quantum information processing

Effects of carrier injection profile on low noise thin Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes

Avalanche photodiodes (APDs) with thin avalanche regions have shown low excess noise characteristics and high gain-bandwidth products, so they are suited for long-haul optical communications. In this work, we investigated how carrier injection profile affects the avalanche gain and excess noise factors of Al0.85Ga0.15As0.56Sb0.44 (lattice-matched to InP substrates) p-i-n and n-i-p diodes with total depletion widths of 145-240 nm. Different carrier injection profiles were achieved by using light with wavelengths of 420, 543 and 633nm. For p-i-n diodes, shorter wavelength light produces higher avalanche gains for a given reverse bias and lower excess noise factors at a given gain, compared to longer wavelength light. Thus, using 420 nm light on the p-i-n diodes, corresponding to pure electron injection conditions, gave the highest gain and lowest excess noise. In n-i-p diodes, pure hole injection yields significantly lower gain and higher excess noise, compared to mixed carrier injection. These show that the electron ionization coefficient, α, is higher than the hole ionization coefficient, β. Using pure electron injection, excess noise factor characteristics with effective ionization ratios, keff, of 0.08-0.1 were obtained. This is significantly lower than those of InP and In0.52Al0.48As, the commonly used avalanche materials combined with In0.53Ga0.47As absorber. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef. DATA: 5787318)

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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Evolution of the upper and lower landing site after endovascular aortic aneurysm repair.

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Strong interfacial exchange field in the graphene/EuS heterostructure

\u3cp\u3eExploiting 2D materials for spintronic applications can potentially realize next-generation devices featuring low power consumption and quantum operation capability. The magnetic exchange field (MEF) induced by an adjacent magnetic insulator enables efficient control of local spin generation and spin modulation in 2D devices without compromising the delicate material structures. Using graphene as a prototypical 2D system, we demonstrate that its coupling to the model magnetic insulator (EuS) produces a substantial MEF (>14 T) with the potential to reach hundreds of tesla, which leads to orders-of-magnitude enhancement of the spin signal originating from the Zeeman spin Hall effect. Furthermore, the new ferromagnetic ground state of Dirac electrons resulting from the strong MEF may give rise to quantized spin-polarized edge transport. The MEF effect shown in our graphene/EuS devices therefore provides a key functionality for future spin logic and memory devices based on emerging 2D materials in classical and quantum information processing.\u3c/p\u3