Apr 30, 2019

Structural investigation of MOVPE-grown GaAs on Ge by x-ray techniques

The selection of appropriate characterization methodologies is vital for analyzing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III–V layers. In this work, we investigate the structural properties of GaAs layers grown by metal-organic vapour phase epitaxy on Ge substrates—(1 0 0) with 6° offset towards 1 1 1〉—under various growth conditions. Synchrotron x-ray topography is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other x-ray techniques, such as reciprocal space mapping and triple axis ω-scans of (0 0 l)-reflections (l = 2, 4, 6), are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by x-ray diffraction (XRD), as well as atomic force microscopy and transmission electron microscopy.


Source:IOPscience

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Apr 24, 2019

Surface activated bonding of GaAs and SiC wafers at room temperature for improved heat dissipation in high-power semiconductor lasers

Thermal management of high-power semiconductor lasers is of great importance since the output power and beam quality are affected by the temperature rise of the gain region. Thermal simulations of a vertical-external-cavity surface-emitting laser by a finite-element method showed that the solder layer between the semiconductor thin film consisting of the gain region and a heat sink has a strong influence on the thermal resistance and direct bonding is preferred to achieve effective heat dissipation. To realize thin-film semiconductor lasers directly bonded on a high-thermal-conductivity substrate, surface-activated bonding using an argon fast atom beam was applied to the bonding of gallium arsenide wafer (GaAs) and silicon carbide (SiC) wafers. The GaAs/SiC structure was demonstrated in the wafer scale (2 in. in diameter) at room temperature. The cross-sectional transmission electron microscopy observations showed that void-free bonding interfaces were achieved.


Source:IOPscience

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Apr 18, 2019

Impact of LT-GaAs layers on crystalline properties of the epitaxial GaAs films grown by MBE on Si substrates

GaAs films with low-temperature GaAs (LT-GaAs) layers were grown by molecular beam epitaxy (MBE) method on vicinal (001) Si substrates oriented 6° off towards [110]. The grown structures were different with the thickness of LT-GaAs layers and its arrangement in the film. The processes of epitaxial layers nucleation and growth were controlled by reflection high energy electron diffraction (RHEED) method. Investigations of crystalline properties of the grown structures were carried out by the methods of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystalline perfection of the GaAs films with LT-GaAs layers and the GaAs films without ones was comparable. It was found that in the LT- GaAs/Si layers the arsenic clusters are formed, as it occurs in the LT-GaAs/GaAs system without dislocation. It is shown that large clusters are formed mainly on the dislocations. However, the clusters have practically no effect on the density and the propagation path of threading dislocations. With increasing thickness of LT-GaAs layer the dislocations are partly bent along the LT-GaAs/GaAs interface due to the presence of stresses.


Source:IOPscience

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Apr 9, 2019

Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.



Source:IOPscience

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Apr 3, 2019

Quantitative thermal wave phase imaging of an IR semi-transparent GaAs wafer using IR lock-in thermography

In this paper, the simultaneous measurement of out-of-plane thermal diffusivity and effective infrared absorption coefficient of an IR semi-transparent GaAs wafer using infrared lock-in thermography technique (LIT) is presented. The method relies on analysis of the generated LIT phase images recorded at different modulation frequencies, using the thermal wave model in the transmission configuration. The out-of-plane thermal diffusivity and effective infrared absorption coefficient are estimated from the best fit of the theoretical model to the experimental data. The obtained values are in good agreement with those obtained by supplementary measurement using the modulated photothermal infrared radiometry technique (PTR) in the reflection mode, and also with data reported in the literature. In addition, simple modification of the LIT experiment set up allows one to determinate the in-plane thermal diffusivity of n-GaAs wafer. It was found that in-plane and out-of-plane thermal diffusivities of the GaAs wafer are very close, as expected, within the limit of measurement errors. The results show that the LIT technique in transmission configuration can provide spatial information about both the (effective) infrared absorption coefficient and thermal diffusivity of semiconductor crystals.



Source:IOPscience


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