## 2019年12月25日星期三

### (Invited) Significant Enhancement of High-Ns Electron Mobility in Ge n-MOSFETs with Atomically Flat Ge/GeO2 Interface

The rapid degradation of high-Ns electron mobility in Ge n-MOSFETs is still one of the greatest concerns in Ge CMOS technology. Although there are many possible origins so far considered, the degradation mechanism is still unclear in spite of its importance. In this work, we clarify wafer-related origins for electron mobility degradation in Ge n-MOSFETs. High-Ns electron mobility is dramatically improved thanks to (i) atomically flat Ge surface formation, followed by (ii) layer-by-layer oxidation. (iii) Oxygen-related neutral impurities in Ge substrates could be another origin of the mobility reduction on Ge wafers. By successfully eliminating these scattering sources in Ge n-MOSFETs, we demonstrate intrinsically high electron mobility in a wide range of Ns.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年12月11日星期三

### Interface characteristics and electrical transport of Ge/Si heterojunction fabricated by low-temperature wafer bonding

We report a promising method for oxide-layer-free germanium (Ge)/silicon (Si) wafer bonding based on an amorphous Ge (a-Ge) intermediate layer between Si and Ge wafers. The effect of the exposure time (t e), during which the a-Ge is exposed to the air after sputtering and being taken out of the chamber on the bubble density at the bonded interface, is identified and a near-bubble-free Ge/Si bonded interface is achieved for the t e of 3 s. The crystallization of a-Ge at Ge/Si bonded interface starts from a-Ge/Ge interface and it fully turns to be single-crystal Ge after post-annealing. The oxide layer at a-Ge/a-Ge bonded interface formed by the interface hydrophilic reaction disappears due to the atom redistribution triggered by the crystallization of a-Ge. As expected, the performance of the Ge/Si heterojunction diode is significantly improved by this oxide-layer-free Ge/Si bonded interface. A low dark current of 1.6 µA, high on/off current ratio of 3.4  ×  105, and low ideality factor of 1.02 (150 K) is achieved at  −0.5 V for the bonded Ge/Si diode. Finally, the carrier transport mechanisms at Ge/Si bonded interface annealed at different temperatures are also clearly clarified.

Source:IOPscience
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年12月4日星期三

### 300 mm SiGe-On-Insulator Substrates with High Ge Content (70%) Fabricated Using the Smart Cut™ Technology

We have fabricated 300 mm Si0.3Ge0.7-On-Insulator substrates with the SmartCutTM approach. The donor wafers consisted in polished, 5 µm thick Si0.3Ge0.7 Strain-Relaxed Buffers (SRBs) on top of Si(001) substrates. The following stacks were deposited on top of those SRBs: (low Ge content SiGe / Si0.3Ge0.7) bilayers and (low Ge content SiGe / Si0.3Ge0.7 / low Ge content SiGe / Si0.3Ge0.7) multilayers. The thin, low Ge content SiGe layers were used as etch stops during the fabrication of the SiGeOI wafers and (in the second case) for the re-use of the expensive SRBs. A slight surface resurgence of the surface cross-hatch occurred as the deposited thicknesses became higher. The Ge content in the epitaxial layers was otherwise closely matched to that in the SRBs (70% instead of 68%) and some O peaks present at the Si0.3Ge0.7 / low Ge content SiGe interfaces. After H+ ion implantation, bonding and splitting, a SC1 solution was used to etch the Si0.3Ge0.7 layers and stop on the low Ge content SiGe layers. Meanwhile, TMAH was used in order to etch the low Ge content SiGe layers and stop on the Si0.3Ge0.7 layers. We obtained in the end 57 nm thick, flat Si0.3Ge0.7 layers (7.4 nm range) on top of the buried oxide (root mean square roughness: 0.3 nm only).

Source:IOPscience
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年11月27日星期三

### 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.]

Source:IOPscience
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年11月19日星期二

### Bubble evolution mechanism and stress-induced crystallization in low-temperature silicon wafer bonding based on a thin intermediate amorphous Ge layer

The dependence of the morphology and crystallinity of an amorphous Ge (a-Ge) interlayer between two Si wafers on the annealing temperature is identified to understand the bubble evolution mechanism. The effect of a-Ge layer thickness on the bubble density and size at different annealing temperatures is also clearly clarified. It suggests that the bubble density is significantly affected by the crystallinity and thickness of the a-Ge layer. With the increase of the crystallinity and thickness of the a-Ge layer, the bubble density decreases. It is important that a near-bubble-free Ge interface, which is also an oxide-free interface, is achieved when the bonded Si wafers (a-Ge layer thickness  ≥  20 nm) are annealed at 400 °C. Furthermore, the crystallization temperature of the a-Ge between the bonded Si wafers is lower than that on a Si substrate alone and the Ge grains firstly form at the Ge/Ge bonded interface, rather than the Ge/Si interface. We believe that the stress-induced crystallization of a-Ge film and the intermixing of Ge atoms at the Ge/Ge interface can be responsible for this feature.

Source:IOPscience
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年11月11日星期一

### Thin film germanium on silicon created via ion implantation and oxide trapping

We present a novel process for integrating germanium with silicon-on-insulator (SOI) wafers. Germanium is implanted into SOI which is then oxidized, trapping the germanium between the two oxide layers (the grown oxide and the buried oxide). With careful control of the implantation and oxidation conditions this process creates a thin layer (current experiments indicate up to 20-30nm) of almost pure germanium. The layer can be used potentially for fabrication of integrated photo-detectors sensitive to infrared wavelengths, or may serve as a seed for further germanium growth. Results are presented from electron microscopy and Rutherford back-scattering analysis, as well as preliminary modelling using an analytical description of the process.

Source:IOPscience
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年11月6日星期三

### 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
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年10月29日星期二

### Fabrication of Ge-on-insulator wafers by Smart-CutTM with thermal management for undamaged donor Ge wafers

Newly engineered substrates consisting of semiconductor-on-insulator are gaining much attention as starting materials for the subsequent transfer of semiconductor nanomembranes via selective etching of the insulating layer. Germanium-on-insulator (GeOI) substrates are critically important because of the versatile applications of Ge nanomembranes (Ge NMs) toward electronic and optoelectronic devices. Among various fabrication techniques, the Smart-CutTM technique is more attractive than other methods because a high temperature annealing process can be avoided. Another advantage of Smart-CutTM is the reusability of the donor Ge wafer. However, it is very difficult to realize an undamaged Ge wafer because there exists a large mismatch in the coefficient of thermal expansion among the layers. Although an undamaged donor Ge wafer is a prerequisite for its reuse, research related to this issue has not yet been reported. Here we report the fabrication of 4-inch GeOI substrates using the direct wafer bonding and Smart-CutTM process with a low thermal budget. In addition, a thermo-mechanical simulation of GeOI was performed by COMSOL to analyze induced thermal stress in each layer of GeOI. Crack-free donor Ge wafers were obtained by annealing at 250 °C for 10 h. Raman spectroscopy and x-ray diffraction (XRD) indicated similarly favorable crystalline quality of the Ge layer in GeOI compared to that of bulk Ge. In addition, Ge p-n diodes using transferred Ge NM indicate a clear rectifying behavior with an on and off current ratio of 500 at ±1 V. This demonstration offers great promise for high performance transferrable Ge NM-based device applications.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年8月21日星期三

### Determination of the free carrier concentration in atomic-layer doped germanium thin films by infrared spectroscopy

Novel silicon photonics applications requiring heavy n-type doping have recently driven a great deal of interest towards the phosphorous doping of germanium. In this work we report on infrared reflectance spectroscopy measurements of the electron density in heavily n-type doped germanium layers obtained by stacking multiple phosphorous δ-layers. Here, we demonstrate that the conventional Drude model of the electrodynamic response of free carriers in metals can be adapted to describe heavily doped semiconductor thin films. Consequently, the effect of the electron density on the plasma frequency, scattering rate and complex permittivity can be investigated.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年8月16日星期五

### Heat capacity of germanium crystals with various isotopic composition

The heat capacity of three pure (n, p2×1016 cm-3) germanium crystals with different isotopic compositions was measured in the temperature range from 2.8 K to 100 K. These samples, one made of enriched 70Ge (95.6%), Ge of natural isotopic composition and n, p < 1014 cm-3, and one of the largest possible isotopic mass variance 70/76Ge (43%/48%) with n, p<1014 cm-3, show a change of the molar heat capacity (and corresponding Debye temperature, θD) as expected from the average mass variation, corresponding to θDM-0.5 (M = molar mass) at low temperatures. The mass effect is best visible around 21.5 K, at the minimum of the corresponding Debye temperatures θD, and amounts to ΔθD = 5.3 K for the difference between the Debye temperatures of 70Ge and 70/76Ge. The specific heat capacity of the natural Ge crystal agrees within 2% with the best data available in the literature taken on much larger masses of Ge.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年8月9日星期五

### Thin germanium–carbon layers deposited directly on silicon for metal–oxide–semiconductor devices

We report the growth process and materials characterization of germanium–carbon alloys (Ge1−xCx) deposited directly on Si (1 0 0) substrates by ultra-high-vacuum chemical vapour deposition. The Ge1−xCx films are characterized by transmission electron microscopy, etch-pit density, x-ray diffraction, secondary ion mass spectrometry and electron energy loss spectroscopy. The results show that the films exhibit low threading dislocation densities despite significant strain relaxation. We also present evidence for carbon segregation in the Ge1−xCx and interpret these results as a strain relaxation mechanism.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年8月1日星期四

### New concept of planar germanium MOSFET with stacked germanide layers at source/drain

In this paper, we have proposed and simulated one novel Schottky barrier germanium-based MOSFET structure. Herein, the source/drain region of the device is consisted with two stacked layers of germanide materials. Different barrier heights of the top and bottom contact are hence formed with channel respectively. The top barrier height is designed lower enough to enlarge drive current, and the bottom barrier height is higher (nearly mid-gap) to diminish the leakage current. The working mechanism and the performance of n- and p-type devices is studied. Comparisons between dual barrier structure and single barrier structure are also carried out. The results show that the characteristics have been significantly enhanced with the proposed dual barrier structure. Besides, the devices' performance is nearly insensitive to germanium thickness, which leads to the relax of the requirement of germanium-on-insulator (GeOI) structures for leakage immunization.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年7月23日星期二

### Characteristics of Germanium-on-Insulators Fabricated by Wafer Bonding and Hydrogen-Induced Layer Splitting

There is considerable interest in germanium-on-insulator (GeOI) because of its advantages in terms of device performance and compatibility with silicon processing. In this paper, fabricating GeOI by hydrogen-induced layer splitting and wafer bonding is discussed. Hydrogen in germanium exists in molecular form and is prone to outdiffusion, resulting in a storage-time dependence of blistering. In contrast to the case of silicon, little effect of substrate doping on blistering is observed in germanium. Hydrogen implantation in germanium creates both {100}- and {111}-type microcracks. These two types of platelets are located in the same region for (111)-oriented wafers, but in different zones for (100) samples. This variation in distribution explains the smoother splitting of (111) surfaces than that of (100) surfaces. Hydrogen implantation also introduces a significant concentration of charged vacancies, which affect dopant diffusion in the transferred germanium film. Boron, with a negligible Fermi-level dependence, shows an identical diffusion profile to that of bulk germanium. In contrast, phosphorus diffusion is enhanced in the fabricated GeOI layers. These results also shed light on the understanding of dopant diffusion mechanisms in germanium.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年7月17日星期三

### Investigation of amorphous germanium contact properties with planar detectors made from USD-grown germanium crystals

The characterization of detectors fabricated from home-grown crystals is the most direct way to study crystal properties. We fabricated planar detectors from high-purity germanium (HPGe) crystals grown at the University of South Dakota (USD). In the fabrication process, a HPGe crystal slice cut from a USD-grown crystal was coated with a high resistivity thin film of amorphous Ge (a-Ge) followed by depositing a thin layer of aluminum on top of the a-Ge film to define the physical area of the contacts. We investigated the detector performance including the I-V characteristics, C-V characteristics and spectroscopy measurements for a few detectors. The results document the good quality of the USD-grown crystals and electrical contacts.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年7月9日星期二

### Infrared and terahertz transmission properties of germanium single crystals

Experimental transmission spectra of samples fabricated of germanium single crystals doped with stibium were registered in the infrared 2.5-25 μm and terahertz 130 μm regions of spectrum. It is shown that doping concentration and treatment of the crystals surface have a noticeable influence on the samples absorption.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年7月5日星期五

### Study on the Properties of High Purity Germanium Crystals

In the crystal growth lab of South Dakota University, we are growing high purity germanium (HPGe) crystals and using the grown crystals to make radiation detectors. As the detector grade HPGe crystals, they have to meet two critical requirements: an impurity level of ~109 to 10 atoms /cm3 and a dislocation density in the range of ~102 to 104 / cm3. In the present work, we have used the following four characterization techniques to investigate the properties of the grown crystals. First of all, an x-ray diffraction method was used to determine crystal orientation. Secondly, the van der Pauw Hall effect measurement was used to measure the electrical properties. Thirdly, a photo-thermal ionization spectroscopy (PTIS) was used to identify what the impurity atoms are in the crystal. Lastly, an optical microscope observation was used to measure dislocation density in the crystal. All of these characterization techniques have provided great helps to our crystal activities.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年6月20日星期四

### Temperature-independent slow carrier emission from deep-level defects in p-type germanium

In the deep-level transient spectroscopy (DLTS) spectra of the 3d-transition metals cobalt and chromium in p-type germanium, evidence is obtained that hole emission from defect levels can occur by two parallel paths. Besides classical thermal emission, we observed a second, slower and temperature-independent emission. We show that this extra emission component allows determining unambiguously whether or not multiple DLTS peaks arise from the same defect. Despite similar characteristics, we demonstrate that the origin of the non-thermal emission is not tunnelling but photoionization related to black-body radiation from an insufficiently shielded part of the cryostat.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年6月14日星期五

### Ultralarge transient optical gain from tensile-strained, n-doped germanium on silicon by spin-on dopant diffusion

The direct band gap optical gain of tensile-strained, highly n-doped germanium on silicon is investigated by femtosecond ultrafast transmittance spectroscopy. A germanium film with 0.22% tensile strain is grown on a silicon substrate by using molecular beam epitaxy. An activated doping concentration up to 4 × 1019 cm−3 is achieved by phosphorus diffusion from a spin-on dopant source. The transmittance of the germanium film is clearly increased upon increasing the pump power. A peak optical gain of up to 5300 cm−1 around 1.7 µm and a gain spectrum broader than 300 nm are obtained. These results show a simple yet promising way to realize gain medium for monolithic-integrated germanium lasers.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年6月5日星期三

### Vertically oriented epitaxial germanium nanowires on silicon substrates using thin germanium buffer layers

We demonstrate a method to realize vertically oriented Ge nanowires on Si(111) substrates. Ge nanowires were grown by chemical vapor deposition using Au nanoparticles to seed nanowire growth via a vapor–liquid–solid growth mechanism. Rapid oxidation of Si during Au nanoparticle application inhibits the growth of vertically oriented Ge nanowires directly on Si. The present method employs thin Ge buffer layers grown at low temperature less than 600 °C to circumvent the oxidation problem. By using a thin Ge buffer layer with root-mean-square roughness of ~ 2 nm, the yield of vertically oriented Ge nanowires is as high as 96.3%. This yield is comparable to that of homoepitaxial Ge nanowires. Furthermore, branched Ge nanowires could be successfully grown on these vertically oriented Ge nanowires by a secondary seeding technique. Since the buffer layers are grown under moderate conditions without any high temperature processing steps, this method has a wide process window highly suitable for Si-based microelectronics.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年5月28日星期二

### nfrared and terahertz transmission properties of germanium single crystals

Experimental transmission spectra of samples fabricated of germanium single crystals doped with stibium were registered in the infrared 2.5-25 μm and terahertz 130 μm regions of spectrum. It is shown that doping concentration and treatment of the crystals surface have a noticeable influence on the samples absorption.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年5月23日星期四

### Germanium layers grown by zone thermal crystallization from a discrete liquid source

It is proposed and investigated a method for growing thin uniform germanium layers onto large silicon substrates. The technique uses the hexagonally arranged local sources filled with liquid germanium. Germanium evaporates on very close substrate and in these conditions the residual gases vapor pressure highly reduces. It is shown that to achieve uniformity of the deposited layer better than 97% the critical thickness of the vacuum zone must be equal to l cr = 1.2 mm for a hexagonal arranged system of round local sources with the radius of r = 0.75 mm and the distance between the sources of h = 0.5 mm.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年5月16日星期四

### Highly boron-doped germanium layers on Si(001) grown by carbon-mediated epitaxy

Smooth and fully relaxed highly boron-doped germanium layers were grown directly on Si(001) substrates using carbon-mediated epitaxy. A doping level of ${N}_{{\rm{A}}}\approx 1.1\times {10}^{20}\,{{\rm{cm}}}^{-3}$ was measured by several methods. Using high-resolution x-ray diffraction we observed different lattice parameters for intrinsic and highly boron-doped samples. A lattice parameter of a Ge:B = 5.653 Å was calculated using the results obtained by reciprocal space mapping around the (113) reflection and the model of tetragonal distortion. The observed lattice contraction was adapted and brought in accordance with a theoretical model developed for ultra-highly boron-doped silicon. Raman spectroscopy was performed on the intrinsic and doped samples. A shift in the first order phonon scattering peak was observed and attributed to the high doping level. A doping level of $(1.28\pm 0.19)\times {10}^{20}\,{{\rm{cm}}}^{-3}$ was calculated by comparison with literature. We also observed a difference between the intrinsic and doped sample in the range of second order phonon scattering. Here, an intense peak is visible at $544.8\,{{\rm{cm}}}^{-1}$ for the doped samples. This peak was attributed to the bond between germanium and the boron isotope 11B.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年5月9日星期四

### The effect of germanium doping on oxygen donors in Czochralski-grown silicon

In this paper the effect of germanium doping on oxygen donors in Czochralski (CZ) silicon has been investigated. It is found that germanium suppresses the formation of thermal donors during annealing at 450 °C, as a result of the reaction of Ge with point defects in CZ silicon. Meanwhile, it is clarified that germanium enhances the formation of new donors in CZ silicon, which is proposed to be a process associated with the nucleation enhancement of oxygen precipitation by germanium doping.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年4月30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.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年4月24日星期三

### Electrical properties of Si/Si bonded wafers based on an amorphous Ge interlayer

An amorphous Ge intermediate layer is introduced into the Si bonded interface to lower the annealing temperature and achieve good electrical characteristics. The interface and electrical characteristics of n-Si/n-Si and p-Si/n-Si junctions manufactured by low-temperature wafer bonding based on a thin amorphous Ge are investigated. It is found that the bubble density tremendously decreases when the a-Ge film is not immersed in DI water. This is due to the decrease of the −OH groups. In addition, when the samples are annealed at 400 °C for 20 h, the bubbles totally disappear. This can be explained by the appearance of the polycrystalline Ge (absorption of H2) at the bonded interface. The junction resistance of the n-Si/n-Si bonded wafers decreases with the increase of the annealing temperature. This is consistent with the recrystallization of the a-Ge when high-temperature annealing is conducted. The carrier transport of the Si-based PN junction annealed at 350 °C is consistent with the trap-assisted tunneling model and that annealed at 400 °C is related to the carrier recombination model.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年4月18日星期四

### Fabrication of Ge-on-insulator wafers by Smart-CutTM with thermal management for undamaged donor Ge wafers

Newly engineered substrates consisting of semiconductor-on-insulator are gaining much attention as starting materials for the subsequent transfer of semiconductor nanomembranes via selective etching of the insulating layer. Germanium-on-insulator (GeOI) substrates are critically important because of the versatile applications of Ge nanomembranes (Ge NMs) toward electronic and optoelectronic devices. Among various fabrication techniques, the Smart-CutTM technique is more attractive than other methods because a high temperature annealing process can be avoided. Another advantage of Smart-CutTM is the reusability of the donor Ge wafer. However, it is very difficult to realize an undamaged Ge wafer because there exists a large mismatch in the coefficient of thermal expansion among the layers. Although an undamaged donor Ge wafer is a prerequisite for its reuse, research related to this issue has not yet been reported. Here we report the fabrication of 4-inch GeOI substrates using the direct wafer bonding and Smart-CutTM process with a low thermal budget. In addition, a thermo-mechanical simulation of GeOI was performed by COMSOL to analyze induced thermal stress in each layer of GeOI. Crack-free donor Ge wafers were obtained by annealing at 250 °C for 10 h. Raman spectroscopy and x-ray diffraction (XRD) indicated similarly favorable crystalline quality of the Ge layer in GeOI compared to that of bulk Ge. In addition, Ge p-n diodes using transferred Ge NM indicate a clear rectifying behavior with an on and off current ratio of 500 at ±1 V. This demonstration offers great promise for high performance transferrable Ge NM-based device applications.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年4月9日星期二

### Al-induced crystallization of amorphous Ge thin films on conducting layer coated glass substrates

The effect of the underlayer on the Al-induced crystallized (AIC) Ge thin film is investigated to achieve a high-quality Ge layer on a conducting-layer-coated glass substrate. We found that the crystal orientation and the grain size of the AIC-Ge layer strongly depend on the underlayer material. We explain that this phenomenon is related to the interfacial energy between Ge and the underlayer material and/or the crystal property of the underlayer material, since the Ge nucleation likely occurs at the interface under the growth condition employed in this study. Among the samples with Al-doped ZnO, ITO, and TiN conducting underlayers, the TiN sample yields the highest crystal quality: the (111) orientation fraction of 96% and the average grain size of approximately 100 µm. Therefore, the selection of the conducting underlayer material is significantly important to design advanced photovoltaic devices based on Ge thin films on glass.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com

## 2019年4月3日星期三

### Fabrication of high quality, thin Ge-on-insulator layers by direct wafer-bonding for nanostructured thermoelectric devices

A simple means of fabricating thin Ge-on-insulator layers(GOI layers) with a strong bond at the Ge/SiO2interface through direct wafer-bonding is described. In this work, high quality Ge/SiO2 bonding was achieved under ambient air and at room temperature as a result of the extremely hydrophilic bonding surfaces obtained by chemical treatment prior to direct bonding. Based on the results of this work, the first-ever bonding mechanism between ammonium hydroxide treated Ge and SiO2/Si wafer surfaces is proposed. In addition, strain generated during post-annealing as a consequence of the significant thermal-expansion mismatch between Ge and SiO2 was gradually relieved by applying a multistep-cooling process. Structural characteristics of the thin GOI layer were analyzed by cross-sectional scanning electron microscopy, Raman spectroscopy, x-ray diffraction and transmission electron microscopy. It was determined that direct wafer-bonding followed by polishing could produce a GOI layer as thin as 156 nm, with sub-nm surface roughness.

Source:IOPscience

For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com