Great enhancement in the excitonic recombination and light extraction of highly ordered InGaN/GaN elliptic nanorod arrays on a wafer scale

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 

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Ge wafer; 

 

• • • • SOURCE:iopscience
        
        
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Wafer level package of Au-Ge system using a Ge chemical vapor deposition (CVD) thin film

Highlights

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A ∼100 nm CVD Ge film was deposited on Si wafer by two-step chemical vapor deposition.

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A wafer level eutectic bonding was used to bond the CVD Ge/Si and Au/Ti/Si wafers.

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

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

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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.

Graphical abstract

Keywords

• Au-Ge; 
• Eutectic bonding; 
• Ge CVD; 
• Two-step deposition; 
• Wafer level package
• • • • SOURCE:Sciencedirect
        
        
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Microstructural and electrical properties of Cu-germanide formed on p-type Ge wafer

Highlights

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Material properties of Cu₃Ge were investigated as a function of RTA temperature.

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Orthorhombic Cu₃Ge was only phase formed, irrespective of RTA temperature.

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RTA at 400 °C led to the formation of Cu₃Ge having highly uniform surface and interface.

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Minimum specific contact resistivity was obtained after RTA process at 400 °C.

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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
    
    
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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

•  Ge wafer; 
 
• XRD; W
• afer-Scale
  • • 
      
    • SOURCE:iopscience.iop.org
      
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One-step green synthesis of high uniform SERS substrate based on Au nanoparticles grown on Ge wafer

Highlights

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Gold nanoparticles on Ge wafer have been fabricated by a one-step green reaction.

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The SERS enhancement factor of Rhodamine 6G reached 4.5 × 10⁶.

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The relative standard deviation of SERS signals is less than 8%.

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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.

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Graphical abstract

• SOURCE:Sciencedirect
  
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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 Γ_box≃2°${}_{}\mathrm{}$ in FWHM, which is observable in the monochromatic neutron diffraction, results in an enhancement in the angle-integrated intensity (I_θ${}_{}$). Besides, I_θ${}_{}$ 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 Γ_box${}_{}$, the small mosaic spread of η≃0.1°$\mathrm{}$, 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
      
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Low-defect metamorphic Si (Ge) epilayers on Si (001) with a buried template of nanocavities for multiple-junction solar cells

Highlights

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Fully relaxed Si(Ge) pseudo-substrates (PSs) grown on implanted Si(001).

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Formations of half-loops of dislocations having 60°segments at the Si(Ge)/Si interface.

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Low threading dislocations densities are observed on HRTEM and AFM images for SiGe PSs.

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Using this technique for manufacture of Ge PS for multi-junction solar cells.

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Abstract

Si (001)-oriented substrates (p-type) were implanted at 10 keV with He⁺ ion doses in the 5×10¹⁵ cm⁻² range. They were annealed at 973 K for 1 h to create a buried layer of nano-sized bubbles. Layers of Si_0.77Ge_0.23 about 215 nm thick were grown by low pressure chemical vapor deposition at 848 K on these silicon wafers. The surface roughness and morphology were checked by atomic force microscopy and optical microscopy before and after etching with a modified Shimmel recipe to reveal etch pit dislocations. The thickness, composition, crystalline quality and relaxation-state of the SiGe layer were assessed by Rutherford backscattering spectroscopy and high-resolution X-ray diffraction. A fully relaxed strain-state was obtained for Si_0.77Ge_0.23layers that did not exhibit the classical cross-hatched pattern morphology while having a threading-dislocations density below 10³ cm⁻². This low dislocation density was confirmed by photoluminescence spectroscopy. From high resolution transmission electron microscopy observations, the quasi-total strain-relief is assumed to take place by emission of dislocation loops protruding down into the Si substrate from the SiGe/Si interface and terminating at void surfaces of the buried-nanoporous layer. Possible annihilation of dislocation segments coming from either the SiGe/Si interface or punched out in glide planes by overpressurized nanobubbles may also occur. This near surface porous Si is well adapted for multiple junction solar cell manufacturing.

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Graphical abstract

Keywords

• Implantation; 
• He⁺; 
• Nano-bubbles; 
• Ge(Si); 
• LPCVD; 
• Strain relaxation
• • • 
      
    • SOURCE:Sciencedirect
      
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