Jul 23, 2019

Titanium/Gold Schottky Contacts on P-Type GaAs Grown on (111)A and (100) GaAs Substrates Using Molecular Beam Epitaxy

The Schottky barrier heights of Ti/Au contacts on p-type GaAs, grown on (111)A and (100) GaAs substrates by molecular beam epitaxy, have been investigated by I-V and C-V techniques. Higher barrier heights are observed for contacts on (111)A GaAs films. Comparison between our results and the ideal Schottky barrier height for Ti on p-type GaAs shows that Ti/Au barrier heights on p-type (111)A GaAs films are closer to the ideal case than the Ti/Au barrier heights on p-type (100) GaAs films. This suggests that the defect densities of the Ti-GaAs interfaces of Ti/Au contacts on (111)A GaAs films are lower than those of identical Ti/Au contacts on (100) GaAs films.



Source:IOPscience

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Jul 17, 2019

Electrical properties of Si-doped GaAs layers grown on (411)A GaAs substrates by molecular beam epitaxy

Electrical properties of Si-doped GaAs layers grown on (411)A GaAs substrates by molecular beam epitaxy (MBE) were investigated for applications to GaAs/AlGaAs resonant tunnelling diodes with atomically flat (411)A GaAs/AlGaAs interfaces over an entire device area. These flat interfaces can be realized by MBE under certain growth conditions (growth temperature Ts=580°C and V/III pressure ratio of less than or equal to 11). When the V/III pressure ratio is high (above 15) for Ts=580°C, Si-doped GaAs on a (411)A substrate showed an n-type conduction similar to conventional Si-doped GaAs on (100) substrates. (411)A GaAs/AlGaAs interfaces grown under this condition, however, cannot become as flat and as superior as conventional (100) GaAs/AlGaAs interfaces. On the other hand, when the V/III pressure ratio is 7, an Si-doped GaAs layer on (411)A showed p-type conduction. In the case of a V/III pressure ratio of 10.5 and Ts=580°C, Si-doped GaAs still showed n-type conduction with the compensation ratio ν ((ND+NA)/(ND-NA)) = 2.3. This result suggests that Si can be used as an n-type dopant in GaAs for GaAs/AlGaAs resonant tunnelling diodes grown on (411)A GaAs substrates with atomically flat (411)A GaAs/AlGaAs interfaces.


Source:IOPscience

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Jul 9, 2019

Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE

We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO2-mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.



Source:IOPscience

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Jul 5, 2019

A bow-tie photoconductive antenna using a low-temperature-grown GaAs thin-film on a silicon substrate for terahertz wave generation and detection


This paper presents heterogeneously integrated bow-tie emitter–detector photoconductive antennas (PCAs) based on low-temperature grown-gallium arsenide (LTG-GaAs) thin-film devices on silicon-dioxide/silicon (SiO2/Si) host substrates for integrated terahertz (THz) systems. The LTG-GaAs thin-film devices are fabricated with standard photolithography and thermal evaporation of metal-contact layers of chromium (Cr), nickel (Ni) and gold (Au). They are etched selectively and separated from their growth GaAs substrate. The LTG-GaAs thin-film devices are then heterogeneously integrated on bow-tie antenna electrodes patterned on the surface of a SiO2/Si host substrate for THz emitters and THz detectors. Cost-effective and selective integration of LTG-GaAs thin-film devices on a Si platform is demonstrated. THz radiation from the fabricated THz PCAs is successfully measured using a pump–probe THz time-domain configuration. The THz temporal duration was measured at full width half maximum of 0.36 ps. Its frequency spectrum exhibits a broadband response with a peak resonant frequency of about 0.31 THz. The demonstration illustrates the feasibility of creating heterogeneously integrated THz systems using separately optimized LTG-GaAs devices and Si based electronics.

Source:IOPscience

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