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Micro-Raman measurements have been carried out in order to study the V/III flux ratio effect in InP/InAlAs/InP heterostructures grown by metal-organic chemical vapor deposition (MOCVD). Photoluminescence (PL) studies in InP/InAlAs/InP heterostructures [1,2] show a strong dependence of the PL band linewidth on V/III molar ratio. In addition to the observation of the two-mode behavior and the disorder activated modes in InAlAs alloy, an analysis of Raman spectra shows a line shape broadening and wavenumber shift of Raman peaks for various V/III molar ratios, with minimum linewidth and lattice mismatch occurring at V/III = 50. Also, a strong dependence on the composition modulation of the AlAs-like longitudinal optic (LO AlAs−like ) phonon was observed due to clustering. Calculation of the in-plane strain shows that the lattice mismatch between the epilayer and the substrate is relatively insensitive to flux ratio variation within the range investigated. Therefore, the high arsenic overpressures used have an insignificant adverse effect on the quality of the hetero-interfaces.
GeSn/Ge p-i-n photodetectors with practical Ge 0.964 Sn 0.036 active layers are theoretically investigated. First, we calculated the electronic band parameters for the heterointerfaces between strained Ge 1−x Sn x and relaxed (001)-oriented Ge. The carrier transport in a p-i-n photodiode built on a ten-period Ge 0.964 Sn 0.036 /Ge multiple quantum well absorber was then analyzed and numerically simulated within the Tsu−Esaki formalism by self-consistently solving the Schrödinger and Poisson equations, coupled to the kinetic rate equations. Photodetection up to a 2.1 μm cut-off wavelength is achieved. High responsivities of 0.62 A W −1 and 0.71 A W −1 were obtained under a reverse bias voltage of −3 V at peak wavelengths of 1550 nm and 1781 nm, respectively. Even for this low Sn-fraction, it is found that the photodetector quantum efficiency (49%@1.55 μm) is higher than those of comparable pure-Ge devices at room temperature. Detectivity of 3.8 × 10 10 cm Hz 1/2 W −1 and 7.9 × 10 10 cm Hz 1/2 W −1 at −1 V and −0.5 V, respectively, is achievable at room temperature for a 1550 nm wavelength peak of responsivity. This work represents a step forward in developing GeSn/Ge based infrared photodetectors.
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