## 2016年9月27日星期二

### Medium-energy ion irradiation of Si and Ge wafers: studies of surface nanopatterning and signature of recrystallization in 100 keV Kr+ bombarded a-Si

We report new and exciting experimental results on ion-induced nanopatterning of a-Si and a-Ge surfaces. The crystalline Si (100) and Ge (100) wafers were amorphized and an a/c interface was developed by pre-irradiation with a 50 keV Ar+ beam at normal incidence with an ion fluence of 5.0 × 1015 ions cm−2. These amorphized surfaces were post-irradiated with Ar+ and Kr+ beams at an angle of 60°. The post irradiation was done with ion fluences of 1.0 × 1017 ions cm−2. For each beam, two energies (50 and 200 keV for Ar+, 100 and 250 keV for Kr+) were chosen to ensure ion stopping in both sides of the a/c interface. Regular nanopatterning (in the form of ripples) is observed on the Ge surface only with the post irradiation of the Kr+ beam. The Si surface showed regular nanopatterning with the irradiation of both beams with two energies. For the ion beams crossing the a/c interface, ripples of higher amplitude and longer wavelength were formed. Further, the irradiation with a heavy beam yielded surface ripples of relatively larger amplitudes. The Raman measurements confirm amorphization of the pre-irradiated surfaces. Surprisingly, the post-irradiated Si surface with the 100 keV Kr+ beam showed evidence of recrystallization. In the paper we discuss the physics at the interface and explain the experimental findings.

Keywords: on-induced nanopatterning;  a-Si and a-Ge surfaces; crystalline Si (100) and Ge (100) wafers;

Source:  Iopscience

## 2016年9月18日星期日

### 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.

Keywords: GaAs wafers ;   epitaxial lift-off (ELO);  X-ray diffraction (XRD);  Ge-on-insulator;     GaAs-on-insulator

Source: iopscience

## 2016年9月11日星期日

### Impact of thermal annealing on Ge-on-Insulator substrate fabricated by wafer bonding

We propose the Ge CMOS photonics platform with Ge-on-Insulator (GOI) substrate on which Ge mid-infrared photonic devices and Ge CMOS transistors can be monolithically integrated. The GOI wafer for the Ge CMOS photonics was fabricated by combining wafer bonding and H ion cut technologies. We studied the effect of thermal annealing on the GOI substrate in terms of crystal quality, surface morphology and electrical property. From Raman spectrum, it was found that the crystal quality of the Ge layer was significantly recovered after a 550 °C annealing in N2 (or O2) ambient for 1 h. Meanwhile, the surface roughness of the GOI substrate remained very low even after the annealing process. As a result, the significant improvements on electrical properties of the GOI substrate were confirmed by Hall measurement results. The carrier density of a GOI Hall device decreases from 2.9×1016 to 8.9×1015 cm−3 and hole mobility increases from 925 to 2295 cm2/V s. These results strongly suggest the necessity of a proper thermal annealing on improving the GOI qualities.

Keywords:  Germanium;  Ge-on-Insulator;  Thermal annealing;  Wafer bonding

Source: Sciencedirect

### Plastically deformed Ge-crystal wafers as elements for neutron focusing monochromator

Plastically deformed Ge-crystal wafers that have the cylindrical shape with a large curvature were characterized by neutron diffraction. The box-type rocking curve of Bragg reflection with the angular width of Γbox ~ 2° in FWHM, which is observable in the monochromatic neutron diffraction, results in an enhancement in the angle-integrated intensity (Iθ). Besides,Iθ efficiently increases by stacking such Ge wafers. In the course of white neutron diffraction, the reflected-beam width near the focus point becomes sharper than the initial beam width. Further, the dependence of the horizontal beam width on the distance between the sample and detector is quantitatively explained by taking account of the large Γbox, the small mosaic spread of η~0.1°, and the thickness of the wafers. On the basis of these characterizations, use of plastically deformed Ge wafers as elements for high-luminance neutron monochromator is proposed.

Keywords:  Plastically deformed Ge wafer;  Neutron monochromator crystal;  Neutron beam focus

Source: Sciencedirect

## Highlights

•A ~100nm CVD Ge film was deposited on Si wafer by two-step chemical vapor deposition.
•A wafer level eutectic bonding was used to bond the CVD Ge/Si and Au/Ti/Si wafers.

•The two-step Ge deposited sample showed uniform film after the eutectic bonding.

•A uniform interface was detected between the bonded wafers using two-step deposition.

•An Au-Ge interlayer formed at the bonded interface, which enhanced bonding quality.

A Ge thin film deposited by chemical vapor deposition (CVD) was used to obtain a uniform bonding between Au and Ge films for applications of wafer level packages (WLPs). This Ge CVD thin film showed selective growth on Au and Cu metals when the substrate has both metal and oxide. A one-step and two-step Ge deposition followed by eutectic bonding method was employed to bond the wafers. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy equipped with an energy dispersive spectroscopy (FESEM-EDS), atomic force microscopy, high resolution Field emission transmission electron microscopy, IR inspection tool and secondary ion mass spectroscopy (SIMS). According to the IR inspection results, the two-step Ge deposited sample showed more uniform film compared to one-step deposition after eutectic bonding. Moreover, an improved bonding quality was obtained from the two-step process. Based on FESEM observations, a uniform and crater-free interface was detected between the bonded 4-inch wafers, in which the presence of Ge beside Au and Si was confirmed by EDS. SIMS profiles proved the formation of a thin Au-Ge interlayer at the bonded interface, which enhanced the bonding conditions.

## 2016年8月31日星期三

### Germanium-based Photonics Offer Promise for Novel Sensors and Faster Internet

Researchers from University of Tokyo have successfully built fundamental components from the semiconductor germanium for integrated photonic circuits that work at mid-infrared wavelengths and could improve Internet speeds

The researchers built the new components from the material germanium (Ge). Like silicon, which is commonly used in conventional near-infrared photonics, germanium is a group IV semiconductor, which means it is in the same column of the periodic table and has similar electrical properties. Germanium has several properties that make it particularly well-suited to transmit and guide mid-infrared light, said Jian Kang, a Ph.D. candidate in the Takagi-Takenaka group in theDepartment of Electrical Engineering and Information Systems, University of Tokyo, Japan.

Germanium has high optical transparency in the mid-infrared range so mid-infrared light can easily pass through it. Compared to silicon, germanium has a number of other optically interesting properties. These include a higher refractive index, which means light passes more slowly through it. Germanium also has a larger third-order nonlinearity, an optical effect that can be exploited to, for example, amplify or self-focus beams of light. It has a stronger free-carrier effect, which means charge carrying electrons and holes in the material can help modulate light. Germanium also has a stronger thermo-optic effect than silicon, which means the refractive index can be more easily controlled with temperature.

“These properties could make Ge-based devices show higher performance or even realize new functionalities in the mid-infrared,” said Kang. Furthermore, recent progress on lasers made from strained-Ge and GeSn-based materials make germanium a promising material for integrating both the light producing and light steering components on the same photonic chip, Kang said.

“Currently, the Ge device performance may be not as good as state-of-the-art Si-based ones, because the study of Ge-based photonic components for mid-infrared is quite new and there remain many issues in the optimization of the fabrication process,” he said. “Nevertheless, we believe that Ge-based devices have intrinsic advantages.”

Keywords: Germanium(Ge),  Silicon, Strained-Ge, GeSn-based materials, Ge-based devices

Source: http://www.ofcconference.org/

### Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell

Low dislocation density Ge wafers grown by a vertical gradient freeze (VGF) method used for the fabrication of multi-junction photovoltaic cells (MJC) have been studied by a whole wafer scale measurement of the lattice parameter, X-ray rocking curves, etch pit density (EPD), impurities concentration, minority carrier lifetime and residual stress. Impurity content in the VGF-Ge wafers, including that of B, is quite low although B2O3 encapsulation is used in the growth process. An obvious difference exists across the whole wafer regarding the distribution of etch pit density, lattice parameter, full width at half maximum (FWHM) of the X-ray rocking curve and residual stress measured by Raman spectra. These are in contrast to a reference Ge substrate wafer grown by the Cz method. The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters.

Keywords: Ge wafer, B2O3 ,  VGF-Ge substrate, multi-junction photovoltaic cells (MJC),  etch pit density (EPD)

Source: Iopscience

## Highlights

First, electrical properties of Pt nanofilms on Ge Schottky diodes have been studied.
Second, we investigated the effect of thermal annealing on the electronic parameters of Pt/n-Ge Schottky diodes.
Third, the effect of interface layer and interface states on the transport properties has been explained.

## Abstract

The Pt nano-film Schottky diodes on Ge substrate have been fabricated to investigate the effect of annealing temperature on the characteristics of the device. The germanide phase between Pt nano-films and Ge substrate changed and generated interface layer PtGe at 573 K and 673 K, Pt2Ge3 at 773 K. The current–voltage(I - V) characteristics of Pt/n-Ge Schottky diodes were measured in the temperature range of 183–303 K. Evaluation of the I - V data has revealed an increase of zero-bias barrier height ΦB0 but the decrease of ideality factor n with the increase in temperature. Such behaviors have been successfully modeled on the basis of the thermionic emission mechanism by assuming the presence of Gaussian distributions. The variation of electronic transport properties of these Schottky diodes has been inferred to be attributed to combined effects of interfacial reaction and phase transformation during the annealing process. Therefore, the control of Schottky barrier height at metal/Ge interface is important to realize high performance Ge-based CMOS devices.

## Keywords

• Schottky diodes
• Ge
• Annealing
• Ideality factor
• Barrier height
• SOURCE:Sciencedirect

## Abstract

We propose the Ge CMOS photonics platform with Ge-on-Insulator (GOI) substrate on which Ge mid-infrared photonic devices and Ge CMOS transistors can be monolithically integrated. The GOI wafer for the Ge CMOS photonics was fabricated by combining wafer bonding and H ion cut technologies. We studied the effect of thermal annealing on the GOI substrate in terms of crystal quality, surface morphology and electrical property. From Raman spectrum, it was found that the crystal quality of the Ge layer was significantly recovered after a 550 °C annealing in N2 (or O2) ambient for 1 h. Meanwhile, the surface roughness of the GOI substrate remained very low even after the annealing process. As a result, the significant improvements on electrical properties of the GOI substrate were confirmed by Hall measurement results. The carrier density of a GOI Hall device decreases from 2.9×1016 to 8.9×1015 cm−3 and hole mobility increases from 925 to 2295 cm2/V s. These results strongly suggest the necessity of a proper thermal annealing on improving the GOI qualities.

## Keywords

• Germanium
• Ge-on-Insulator
• Thermal annealing
• Wafer bonding
• SOURCE:Sciencedirect

## Abstract

A series of highly ordered c-plane InGaN/GaN elliptic nanorod (NR) arrays were fabricated by our developed soft UV-curing nanoimprint lithography on a wafer. The photoluminescence (PL) integral intensities of NR samples show a remarkable enhancement by a factor of up to two orders of magnitude compared with their corresponding as-grown samples at room temperature. The radiative recombination in NR samples is found to be greatly enhanced due to not only the suppressed non-radiative recombination but also the strain relaxation and optical waveguide effects. It is demonstrated that elliptic NR arrays improve the light extraction greatly and have polarized emission, both of which possibly result from the broken structure symmetry. Green NR light-emitting diodes have been finally realized, with good current–voltage performance and uniform luminescence.

## Keywords

InGaN/GaN
•
•
• Ge wafer
•
• SOURCE:iopscience

## Highlights

A ∼100 nm CVD Ge film was deposited on Si wafer by two-step chemical vapor deposition.
A wafer level eutectic bonding was used to bond the CVD Ge/Si and Au/Ti/Si wafers.
The two-step Ge deposited sample showed uniform film after the eutectic bonding.
A uniform interface was detected between the bonded wafers using two-step deposition.
An Au-Ge interlayer formed at the bonded interface, which enhanced bonding quality.

## Abstract

A Ge thin film deposited by chemical vapor deposition (CVD) was used to obtain a uniform bonding between Au and Ge films for applications of wafer level packages (WLPs). This Ge CVD thin film showed selective growth on Au and Cu metals when the substrate has both metal and oxide. A one-step and two-step Ge deposition followed by eutectic bonding method was employed to bond the wafers. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy equipped with an energy dispersive spectroscopy (FESEM-EDS), atomic force microscopy, high resolution Field emission transmission electron microscopy, IR inspection tool and secondary ion mass spectroscopy (SIMS). According to the IR inspection results, the two-step Ge deposited sample showed more uniform film compared to one-step deposition after eutectic bonding. Moreover, an improved bonding quality was obtained from the two-step process. Based on FESEM observations, a uniform and crater-free interface was detected between the bonded 4-inch wafers, in which the presence of Ge beside Au and Si was confirmed by EDS. SIMS profiles proved the formation of a thin Au-Ge interlayer at the bonded interface, which enhanced the bonding conditions.

## Keywords

• Au-Ge
• Eutectic bonding
• Ge CVD
• Two-step deposition
• Wafer level package
• SOURCE:Sciencedirect

## Highlights

Material properties of Cu3Ge were investigated as a function of RTA temperature.
Orthorhombic Cu3Ge was only phase formed, irrespective of RTA temperature.
RTA at 400 °C led to the formation of Cu3Ge having highly uniform surface and interface.
Minimum specific contact resistivity was obtained after RTA process at 400 °C.
After 700 °C, inverted pyramidal Cu3Ge islands aligned along Ge <110> were epitaxially grown on Ge.

## Abstract

We have investigated the microstructural and electrical properties of Cu-germanides formed by the deposition of Cu on Ge wafer, followed by rapid thermal annealing (RTA) process at the temperatures in the range of 300–700 °C. Regardless of RTA temperature, the Cu3Ge was the only phase formed as a result of solid-state reaction between Cu and Ge driven by RTA process. The RTA temperature dependency of specific contact resistivity of Cu3Ge was explained in terms of its structural evolution caused by RTA process. The RTA process at 400 °C led to the formation of Cu3Ge film having highly uniform surface and interface morphologies, allowing the minimum value of the specific contact resistivity. The samples annealed above 500 °C underwent the severe structural degradation of Cu3Ge, resulting in a rapid increase in the specific contact resistivity. After RTA at 700 °C, pyramidal Cu3Ge islands standing on a corner, distributed along Ge <110> direction were formed with epitaxial relationship on underlying Ge.

## Keywords

• Cu-germanide
• RTA
• Agglomeration
• Epitaxial Cu3Ge
• Specific contact resistivity
• SOURCE:Sciencedirect

## 2016年3月29日星期二

### 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.

## Highlights

Gold nanoparticles on Ge wafer have been fabricated by a one-step green reaction.
The SERS enhancement factor of Rhodamine 6G reached 4.5 × 106.
The relative standard deviation of SERS signals is less than 8%.

## Abstract

Highly sensitive, large-area and uniform surface-enhanced Raman scattering (SERS) substrates based on gold nanoparticles grown on Ge wafer have been fabricated by a one-step green reaction. The results showed that these substrates exhibited admirable performance in the low concentration detection (1 × 10−7 M) of Rhodamine 6G with the enhancement factor of 4.5 × 106 and remarkable uniformity with relative standard deviation less than 8%. The uniform enhancement was also obtained in the aqueous detection of malachite green. During the experiments, the Raman spectra were recorded in the solution to pursue the uniformity, reproducibility and stability of signals.

## Graphical abstract

### Plastically deformed Ge-crystal wafers as elements for neutron focusing monochromator

Plastically deformed Ge-crystal wafers that have the cylindrical shape with a large curvature were characterized by neutron diffraction. The box-type rocking curve of Bragg reflection with the angular width of Γbox≃2° in FWHM, which is observable in the monochromatic neutron diffraction, results in an enhancement in the angle-integrated intensity (Iθ). Besides, Iθ efficiently increases by stacking such Ge wafers. In the course of white neutron diffraction, the reflected-beam width near the focus point becomes sharper than the initial beam width. Further, the dependence of the horizontal beam width on the distance between the sample and detector is quantitatively explained by taking account of the large Γbox, the small mosaic spread of η≃0.1°, and the thickness of the wafers. On the basis of these characterizations, use of plastically deformed Ge wafers as elements for high-luminance neutron monochromator is proposed.