Analysis of the surface state of epi-ready Ge wafers

The surface state of Ge epi-ready wafers (such as those used on III–V multijunction solar cells) supplied by two different vendors has been studied using X-ray photoemission spectroscopy. Our experimental results show that the oxide layer on the wafer surface is formed by GeO and GeO₂. This oxide layer thickness differs among wafers coming from different suppliers. Besides, several contaminants appear on the wafer surfaces, carbon and probably chlorine being common to every wafer, irrespective of its origin. Wafers from one of the vendors show the presence of carbonates at their surfaces. On such wafers, traces of potassium seem to be present too.

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Highlights

► Ge epi-ready wafers from two different vendors studied using X-ray spectroscopy. ► Oxide layer on all the Ge wafer surfaces formed by GeO and GeO₂; layer thickness depending on wafer vendor. ► Probable presence of chlorine at the wafer surfaces. ► Wafer surfaces from one of the vendors contaminated by carbonates.

Keywords

• Germanium wafers; 
• III–V solar cells; 
• Photoelectron spectroscopy
• 
  
• Source: PAM-XIAMEN
  
  
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• , please visit our website:http://www.qualitymaterial.net , send us email at powerwaymaterial@gmail.com.

Surface blistering of low temperature annealed hydrogen and helium co-implanted germanium and its application to splitting of bonded wafer substrates

Applications involving transfer of germanium layers to silicon-based substrates often require a process involving a restricted thermal budget. The use of relatively low temperatures has a major advantage in reducing stresses when thermal splitting of implanted germanium wafers bonded to silicon-based substrates is used to create germanium-on-oxide (GeOI) layers. The present study investigates the phenomenon of blistering of hydrogen and helium co-implanted germanium over the temperature range 250–400 °C, optical microscopy being used to detect the initial appearance of the blisters. Results showed that plots of Ln(time) vs. blister initiation temperature consisted of several straight-line regions yielding an activation energy for each region. The plots showed similarities to those observed in previous work with silicon co-implanted and annealed under similar conditions. At temperatures below the blister initiation temperature, transmission electron microscopy (TEM), revealed the presence of spherical bubbles at a depth below the surface estimated to be approximately that of the hydrogen implant projected range. GeOI layers were produced by thermal splitting of co-implanted germanium wafers bonded to oxide-coated silicon substrates wafers at a temperature of 300 °C. The RMS roughness of the split germanium surface measured by atomic force microscopy (AFM) was about 11 nm averaged over the wafer surface. In addition there were isolated and randomly distributed regions of 27 nm roughness covering about 20% of the total surface area of the wafer.

Keywords

• Germanium; 
• GeOI; 
• Blistering; 
• Layer transfer; 
• Co-implantation; 
• Implantation
• • • 
      
    • SOURCE:SCIENCEDIRECT
    • 
      
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Germanium: From the first application of Czochralski crystal growth to large diameter dislocation-free wafers

Being the pioneer material in the history of electronics, germanium has regained a lot of interest as a semiconductor material for opto-electronic and electronic applications. We present how developments in the growth of germanium single crystals and the processing of crystals into wafers have enabled the optimal exploitation of the properties of germanium for applications in infrared optics and gamma-radiation detection, and the breakthrough of this material as a substrate for opto-electronic applications like photovoltaics. Germanium might even be on the verge of a come-back in electronics: recent developments show that germanium is a promising material for next generation nanoscale electronic devices and integration of optical functions on logic circuits. In order to achieve compatibility with the state-of-the-art Si environment, we have developed our dislocation-free crystal growth and wafer processing towards the production of 300 mm Ge wafers.

Keywords

• Germanium; 
• Crystal growth; 
• Wafers; 
• Dislocation-free
• 
  
• SOURCE:SCIENCEDIRECT
• 
  
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Assessment of the overall resource consumption of germanium wafer production for high concentration photovoltaics

The overall resource requirements for the production of germanium wafers for III–V multi-junction solar cells applied in concentrator photovoltaics have been assessed based on up to date process information. By employing the cumulative energy demand (CED) method and the cumulative exergy extraction from the natural environment (CEENE) method the following resources have been included in the assessment: fossil resources, nuclear resources, renewable resources, land resources, atmospheric resources, metal resources, mineral resources and water resources. The CED has been determined as 216 MJ and the CEENE has been determined as 258 MJ_ex. In addition partial energy and exergy payback times have been calculated for the base case, which entails the installation of the high concentration photovoltaics (HCPVs) in the Southwestern USA, resulting in payback times of around 4 days for the germanium wafer production. Due to applying concentration technology the germanium wafer accounts for only 3% of the overall resource consumption of an HCPV system. A scenario analysis on the electricity input to the wafer production and on the country of installation of the HCPV has been performed, showing the importance of these factors on the cumulative resource consumption of the wafer production and the partial payback times.

Highlights

• The Ge-wafer production for concentrator solar cells was inventoried and assessed. • The cumulative energy demand was determined as 216 MJ wafer⁻¹. • The cumulative exergy extraction from the natural environment was 258 MJ_ex wafer⁻¹. • System installation in the SW USA results in Ge-wafer payback times of ca. 4 days. • The Ge-wafer represents only 3% of the concentrator PV system resource requirements.

Keywords

• Payback time; 
• Germanium wafer; 
• High concentration photovoltaics (HCPVs); 
• Life-cycle assessment;
• Cumulative energy demand (CED); 
• Cumulative exergy extraction from the natural environment (CEENE)

• Source: Sciencedirect

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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.

Keywords:germanium diode,detector germanium,silicon germanium,germanium transistor,element germanium,

germanium n type wafer,germanium production

Source: PAM-XIAMEN

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Germanium Substrate of Optical Grade

Xiamen Powerway Advanced Material Co.,Ltd., a leading supplier of Germanium Substrate materials and other related products and services, can provide Germanium Substrate of Optical Grade in different size.And now PAM-XIAMEN offer specification as follows:

SL.No	Material Specifications:
1	Crystalline Form :	Polycrystalline
2	Conductivity Type :	n-type
3	Absorption Coefficient, at 25°C	0.035cm-1 max @ 10.6µm
4	Typical Resistivity :	3-40 ohm-cm
5	Density :	5.3 g/cc
6	Mohs Hardness :	6.3
7	Oxygen Content :	< 0.03 ppm
8	Holes and Inclusions:	<0.05 mm
9	Poisson Ratio :	0.278
10	Youngs Modulus (E) :	100 Gpa

SL.No	Optical Properties:
1	dn/dt  from 250-350 K :	4 X 10-4 K-1
2	Transmission at 25°C @10.6 µm wavelength
	for uncoated sample of thickness 10mm :	Max. 47% or more
3	Refractive Index @ 10.8 µm :	4.00372471±0.0005
4	Inhomogeneity of the Index :	2 X 10-4

                                                                                                                                                                            

SL.No	Thermal Properties
1	Melting Point (K) :	1210.4
2	Heat Capacity @ 300K (J/kg.K):	322
3	Thermal Conductivity @293 K :	59 Wm-1 K-1
4	Coefficient Thermal Expansion @ (20°C) (10-6 K):	5.8

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Germanium on sapphire by wafer bonding

This paper describes the creation of a germanium on sapphire platform, via wafer bonding technology, for system-on-a-chip applications. Similar thermal coefficients of expansion between germanium (5.8 × 10−6 K−1) and sapphire (5 × 10−6 K−1) make the bonding of germanium to sapphire a reality. Germanium directly bonded to sapphire results in microvoid generation during post bond annealing. Inclusion of an interface layer such as silicon dioxide layer by plasma enhanced chemical vapour deposition, prior to bonding, results in a microvoid free bond interface after annealing. Grinding and polishing of the subsequent germanium layer has been achieved leaving a thick germanium on sapphire (GeOS) substrate. Submicron GeOS layers have also been achieved with hydrogen/helium co-implantation and layer transfer. Circular geometry transistors exhibiting a field effect mobility of 890 cm2/V s have been fabricated onto the thick germanium on sapphire layer.

Keywords:Germanium; Sapphire; Wafer bonding

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.

more detail...

VGF growth of germanium single crystals without crucible contact

Experimental results on the vertical gradient freeze growth of germanium single crystals without crucible contact are presented. Two different approaches to establish a stable pressure difference necessary for avoiding the contact between crystal and crucible on solidification are described. Germanium crystals with a diameter of up to 3 in were grown almost without contact to the crucible wall. The effect of detachment is discussed with respect to the microscopical surface roughness and dislocation density of the grown crystals. In comparison to conventionally grown reference crystals the structural perfection of the detached-grown crystals is found to be much higher which can be attributed to the reduced thermal and thermo-mechanical stress in growth without wall contact.

Source: Journal of Crystal Growth

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Czochralski-growth of germanium crystals containing high concentrations of oxygen impurities

Oxygen-containing germanium (Ge) single crystals with low density of grown-in dislocations were grown by the Czochralski (CZ) technique from a Ge melt, both with and without a covering by boron oxide (B₂O₃) liquid. Interstitially dissolved oxygen concentrations in the crystals were determined by the absorption peak at 855 cm⁻¹ in the infrared absorption spectra at room temperature. It was found that oxygen concentration in a Ge crystal grown from melt partially or fully covered with B₂O₃ liquid was about 10¹⁶ cm⁻³ and was almost the same as that in a Ge crystal grown without B₂O₃. Oxygen concentration in a Ge crystal was enhanced to be greater than 10¹⁷ cm⁻³ by growing a crystal from a melt fully covered with B₂O₃; with the addition of germanium oxide powder, the maximum oxygen concentration achieved was 5.5×10¹⁷ cm⁻³. The effective segregation coefficients of oxygen in the present Ge crystal growth were roughly estimated to be between 1.0 and 1.4.

Source: Journal of Crystal Growth

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Double-hump diffusion profiles of copper and nickel in germanium wafers yielding vacancy-related information

Diffusion of Cu and Ni into Ge was investigated between 700 and 900 °C with the aid of rapid isothermal lamp annealing and spreading-resistance profiling. Using low-dislocation-density single-crystal Ge wafers with a backside gold layer, we observed typical double-hump diffusion profiles of both Cu and Ni. These profiles can be described within the dissociative model by taking into account that the front surface acts as source for both vacancies (V) and Cu or Ni while the back surface combines the V-source feature with a Cu, Ni-sink property. Profile fitting yields data regarding the V-assisted Ge self-diffusion coefficient and the equilibrium concentration of vacancies as a function of temperature.

Source:IEEE

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Automatic measurement of thickness as applied to germanium wafer production in transistor manufacture

The paper first examines the problems involved in the measurement of the thickness of germanium wafers, the difficulties encountered in handling and manoeuvring them due to their small size and weight and the nature of their material composition. Errors and failings in hand measurement are discussed, together with the advantages of mechanical measurement. The design and construction of an automatic measuring machine are then described, showing how the wafers are measured, sorted into seven different sizes and counted. The movement of them to the measuring point is by mechanical means, but they are measured, sorted and counted electronically. Measurement is effected by an electronic comparator of high magnification and accuracy, the output signal of which is amplified and then used to operate the sorting mechanism. Some half-million wafers were measured during the development period, which is described, together with the difficulties encountered and the modifications found necessary finally to produce the consistency and accuracy of measurement required. In conclusion, the assets of the machine in eliminating human error in hand measurement and operator fatigue, together with its production capacity, are described.

Source:IEEE

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Large diameter germanium wafers for CPV applications

Umicore has a long tradition in supplying germanium wafers to the space solar cell market. The main product for this application up to today is a substrate with a diameter of 100 mm and a thickness in the range of 140 – 180 ¼m. With the new emerging market of high-efficiency concentrator photovoltaics (CPV) the need has arisen to investigate the use of germanium wafers with a larger diameter. Especially for small size CPV cells, increasing the wafer diameter will significantly reduce the processing cost per die, which will also contribute to lowering the overall cost/kWh of CPV technology. In this paper the development of dislocation free 150 mm germanium wafers for CPV applications is presented. Different wafer thicknesses down to 200 ¼m have been realized. The process steps starting from crystal pulling up to final epi-cleaning and drying will be addressed. First measurement results on wafer level are shown as well. Finally, the future challenges in optimizing the 150 mm waferspecifications will be reviewed.

Source:IEEE

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X-ray Diffraction Topography of Germanium Wafers

X-ray diffraction topography in transmission and reflection has been employed to analyze crystal faults and stresses in germanium wafers caused by deposition of oxide layers, epitaxy and planar diffusion. Localized diffusion of arsenic, gallium and phosphorus normally does not introduce stresses sufficiently high to generate dislocations in germanium (011) wafers. However, heat treatment of germaniumwafers covered with a SiO2 film causes high stresses which are often relieved by plastic deformation.

Source:IEEE

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High performance n+/p and p+/n germanium diodes at low-temperature activation annealing

In this work we demonstrate the fabrication and characterization of high performance junction diodes using annealing temperatures within the temperature range of 300–350 °C. The low temperature dopant activation was assisted by a 50 nm platinum layer which transforms into platinum germanide during annealing. The fabricated diodes exhibited high forward currents, in excess of 400 A/cm² at ∼|0.7| V for both p⁺/n and n⁺/p diodes, with forward to reverse ratio I_F/I_R greater than 10⁴. Best results for the n⁺/p junctions were obtained at the lower annealing temperature of 300 °C. These characteristics compare favorably with the results of either conventional or with Ni or Co assisted dopant activation annealing. The low-temperature annealing in combination with the high forward currents at low bias makes this method suitable for high performance/low operating power applications, utilizing thus high mobility germanium substrates.

Source: Microelectronic Engineering

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A facility for plastic deformation of germanium single-crystal wafers

A facility for plastic deformation of single-crystal germanium wafers is described. It consists of a commercial tube furnace which radiates heat to evacuated quartz-glass tubes housing the tools for bending and flattening of the wafers. The facility is semi-automatic and requires minimal attention. All movements and temperature changes are done by a robot via a PLC-control system. Two nine-crystal focusing monochromators (54 × 116 and 70 × 116 mm²) made from 100 wafers with average mosaicity ∼13′ have been constructed. Summaries of the test results are presented.

Source: Physica B: Condensed Matter

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Ambient stability of wet chemically passivated germanium wafer for crystalline solar cells

Surface passivation has been recognized as a crucial step in the evaluation of minority carrier lifetime of photovoltaic materials as well as in the fabrication of high efficient solar cells. Dilute acids of HF and HCl are employed for germanium (Ge) surface passivation. An effective lifetime of passivated Ge wafers has been evaluated by a microwave photoconductive decay (μ-PCD) measurement. Surface recombination velocities,S, of H- and Cl-terminated Ge surfaces are 23 and 37 cm/s, respectively. The stability of passivated Ge surfaces against exposure to air has also been examined. The HCl-passivated Ge surfaces are found to be more robust than HF-passivated surfaces.

Source: Solar Energy Materials and Solar Cells

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High mobility single-crystalline-like germanium thin films on flexible, inexpensive substrates

Single-crystalline-like epitaxial germanium thin films with hall mobility values as high as 833 cm²/Vs have been demonstrated on inexpensive polycrystalline metallic substrates. The dependence of mobility of p-type and n-type germanium films on the deposition temperature has been examined and correlated to microstructural changes. The importance of crystallographic orientation of Ge to achieve these high mobility values has been verified. The mobilities of the epitaxial germanium films on the film thickness for p-type and n-type films with multi-layer architecture with different epitaxial intermediate layers have been investigated. Results show that the increased mobility with increasing germanium film thickness is not just due to crystallographic texture improvement, but could also be a result of decreasing defect density.
Highlights

► Single-crystalline-like films of p-Ge and n-Ge on flexible, inexpensive substrates

► p-Ge and n-Ge films with mobility of 833 and 343 cm²/Vs on these substrates

► Ge grain size, (400) peak intensity, and hall mobility increase rapidly above 630 °C.

► Hole mobility increases and defect density decreases with increasing Ge thickness.

Source:Thin Solid Films

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Deposition of copper, silver and gold from aqueous solutions onto germanium substrates via galvanic displacement

Deposition of copper, silver and gold from aqueous solutions onto germanium substrates is studied in this work. For this purpose both acidic and alkaline solutions were used. All investigated metals can successfully be deposited via the galvanic displacement reaction. These deposits are porous and with different surface morphologies which depended on the type (p- or n-) of the Ge substrate used in the experiments and on pH. Prolonged times of immersion of Ge substrates into investigated solutions may lead to a formation of more porous coatings and even powders, as successfully demonstrated on the example of silver. It is believed that the approach presented in this work should further be investigated as an activation step for a possible metallization of Ge substrates via autocatalytic or electrodeposition methods.

Source:Electrochimica Acta

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Germanium on insulator near-infrared photodetectors fabricated by layer transfer

We report on novel pn Ge photodetectors fabricated on glass. The fabrication consists of wafer bonding and layer splitting, followed by a low-temperature epitaxial growth of Ge. The photodiodes are characterized in terms of dark current and responsivity, and their performance compared with devices realized on either Ge or Si. The minimum current density is 50 μA/cm² at 1 V reverse bias, the responsivity is 0.2 A/W in the photovoltaic mode, with a maximum of 0.28 A/W at 1.55 μm at a reverse voltage of 5 V.

Source:Thin Solid Films

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This paper describes the creation of a germanium on sapphire platform, via wafer bonding technology, for system-on-a-chip applications. Similar thermal coefficients of expansion between germanium (5.8 × 10⁻⁶ K⁻¹) and sapphire (5 × 10⁻⁶ K⁻¹) make the bonding of germanium to sapphire a reality. Germanium directly bonded to sapphire results in microvoid generation during post bond annealing. Inclusion of an interface layer such as silicon dioxide layer by plasma enhanced chemical vapour deposition, prior to bonding, results in a microvoid free bond interface after annealing. Grinding and polishing of the subsequent germanium layer has been achieved leaving a thick germanium on sapphire (GeOS) substrate. Submicron GeOS layers have also been achieved with hydrogen/helium co-implantation and layer transfer. Circular geometry transistors exhibiting a field effect mobility of 890 cm²/V s have been fabricated onto the thick germanium on sapphire layer.

Source:Solid-State Electronics

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