Aug 21, 2019

Comparison of self-assisted VLS GaAs nanowires grown by MBE on Si (111) and GaAs (111)B substrates

In this work GaAs nanowires were grown by self-assisted growth method with completely identical growth parameters, such as growth temperature, growth time, Ga and As flux, on GaAs (111)B and Si (111) substrates using Molecular Beam Epitaxy (MBE). All samples were then characterized by Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX), and X-ray Diffraction (XRD). The results from both substrates were compared in order to understand the effect of substrate type on nanowires.

Source:IOPscience

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Aug 16, 2019

Highly efficient photoconductive antennas using optimum low-temperature-grown GaAs layers and Si substrates

We have improved the efficiency of photoconductive antennas (PCAs) using low-temperature-grown GaAs (LT-GaAs). We found that the physical properties of LT-GaAs photoconductive layers greatly affect the generation and detection characteristics of terahertz (THz) waves. In THz generation, high photoexcited carrier mobility and the presence of a few As clusters in the LT-GaAs are two important factors. In detection, short carrier lifetime and the absence of a polycrystalline structure in the LT-GaAs are significant factors. By optimizing these physical properties, we improved the total dynamic range of THz generation and detection by 15 dB over that obtained by conventional commercially available PCAs. In addition, we replaced the semi-insulating GaAs (SI-GaAs) substrate with a Si substrate, which has a low absorption in the THz region. We proposed a new idea of including a highly insulating Al0.5Ga0.5As buffer layer on the Si substrate. Finally, we confirmed the feasibility of manufacturing PCAs using Si substrates.

Source:IOPscience


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Aug 9, 2019

InGaAs quantum dots grown on B-type high index GaAs substrates: surface morphologies and optical properties

We systematically investigated the correlation between morphological and optical properties of InGaAs self-assembled quantum dots (QDs) grown by solid-source molecular beam epitaxy on GaAs (n 11)B (n = 9, 8, 7, 5, 3, 2) substrates. Remarkably, all InGaAs QDs on GaAs(n 11)B under investigation show optical properties superior to those for ones on GaAs(100) as regards the photoluminescence (PL) linewidth and intensity. The morphology for growth of InGaAs QDs on GaAs (n 11)B, where n = 9, 8, 7, 5, is observed to have a rounded shape with a higher degree of lateral ordering than that on GaAs(100). The optical property and the lateral ordering are best for QDs grown on a (511)B substrate surface, giving a strong correlation between lateral ordering and PL optical quality. Our results demonstrate the potential for high quality InGaAs QDs on GaAs(n 11)B for optoelectronic applications.


Source:IOPscience

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Aug 1, 2019

Dark current characteristics of GaAs-based 2.6 µm InGaAs photodetectors on different types of InAlAs buffer layers

GaAs-based In0.83Ga0.17As photodetectors (PDs) with cut-off wavelengths up to 2.6 µm are demonstrated. The effects of continuously-graded or fixed-composition InAlAs buffers on the device performances are investigated. The dark current characteristics of the PDs at various temperatures are analysed in detail. The photocurrents are also measured at 300 K; the detectivity of the PDs is extracted. The two GaAs-based PDs with different buffer schemes show different temperature-dependent dark current behaviours. The around room temperature performances of the GaAs-based device on the fixed-composition buffer are not as good, but comparable to those of InP-based devices, revealing a promising candidate for the GaAs-based PDs and focal plane arrays for many low-end applications.



Source:IOPscience

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