Sb mediated formation of Ge/Si quantum dots: Growth and properties

The phenomenon of surfactant (Sb) mediated formation of Ge/Si(100) islands (quantum dots) by means of molecular beam epitaxy is discussed. The limited diffusivity of Si and Ge adatoms caused by the Sb layer leads to a reduction of the size of Ge islands, the increase in the island density, and the sharpening of the interfaces of Ge islands. Thereby, a thin Sb layer is considered to be a powerful tool that provides more freedom in designing Ge quantum dot features. Ge quantum dots, grown via a thin Sb layer and embedded coherently in a Si p-n junction, are revealed to be the origin of the intense photo- and electroluminescence in the spectral range of about 1.5 μm at room temperature.     

Investigation of Sb diffusion in amorphous silicon

Amorphous silicon materials and its alloys became extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry. Amorphous Si/Si_1−xSb_x/Si tri-layer samples with 5 at% antimony concentration were prepared by direct current magnetron sputtering onto Si substrate at room temperature. Annealing of the samples was performed at different temperatures in vacuum (p<10⁻⁷ mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent of diffusion, the evaluated diffusion coefficients are in the range of ∼10⁻²¹ m²s⁻¹ at 550 °C.     

Structural characterization of fluidized bed nitrided steels

The nitriding behaviour of 34CrAlNi7, 42CrMo4 and 40CrMnMoS86 steels was investigated nitrided in the fluidized bed processes. The nitriding processes were carried out at a temperature of 575 °C for treatment times of 6, 12 and 18 h. The nitrided samples were fully characterized using metallographic, microhardness and XRD techniques. Test results indicated that thickness of the compound layer on the steel surface changed in the range from 10 to 18 μm depending on steel type and treatment time, and γ′-Fe₄N and ε-Fe₂₋₃N formed in the compound layer. The hardness of the diffusion layer was over 1000 HV. Depending on the chemical composition of steels, the case depth ranged from 155 to 525 μm. Kinetics studies showed that the effective diffusion coefficients are 298×10⁻¹⁴, 525×10⁻¹⁴ and 68.8×10⁻¹⁴ m² s⁻¹, for 34CrAlNi7, 42CrMo4 and 40CrMnMoS86 steels, respectively. The fluidized bed process realizes the highest hardness of the case layer, 1095 HV, with fairly high growth rates, 27 μm/h.     

High quality Ge epitaxial layers on Si by ultrahigh vacuum chemical vapor deposition

Flat, relaxed Ge epitaxial layers with low threading dislocation density (TDD) of 1.94 × 10⁶ cm^− 2 were grown on Si(001) by ultrahigh vacuum chemical vapor deposition. High temperature Ge growth at 500 °C on 45 nm low temperature (LT) Ge buffer layer grown at 300 °C ensured the growth of a flat surface with RMS roughness of 1 nm; however, the growth at 650 °C resulted in rough intermixed SiGe layer irrespective of the use of low temperature Ge buffer layer due to the roughening of LT Ge buffer layer during the temperature ramp and subsequent severe surface diffusion at high temperatures. Two-dimensional Ge layer grown at LT was very crucial in achieving low TDD Ge epitaxial film suitable for device applications.     

High performance infra-red detectors based on Si/SiGe multilayers quantum structure

Recently, single crystalline (Sc) Si/SiGe multi quantum structure has been recognized as a new low-cost thermistor material for IR detection. Higher signal-to-noise (SNR) ratio and temperature coefficient of resistance (TCR) than existing thermistor materials have converted it to a candidate for infrared (IR) detection in night vision applications. In this study, the effects of Ge content, C doping and the Ni silicidation of the contacts on the performance of SiGe/Si thermistor material have been investigated. Finally, an uncooled thermistor material with TCR of −4.5%/K for 100 μm × 100 μm pixel sizes and low noise constant (K_1/f) value of 4.4 × 10⁻¹⁵ is presented. The outstanding performance of the devices is due to Ni silicide contacts, smooth interfaces, and high quality multi quantum wells (MQWs) containing high Ge content.     

Low threading dislocation Ge on Si by combining deposition and etching

Blanket and selective Ge growth on Si is investigated using reduced pressure chemical vapor deposition. To reduce the threading dislocation density (TDD) at low thickness, Ge deposition with cyclic annealing followed by HCl etching is performed. In the case of blanket Ge deposition, a TDD of 1.3 × 10⁶ cm^− 2 is obtained, when the Ge layer is etched back from 4.5 μm thickness to 1.8 μm. The TDD is not increased relative to the situation before etching. The root mean square of roughness of the 1.8 μm thick Ge is about 0.46 nm, which is of the same level as before HCl etching. Further etching shows increased surface roughness caused by non-uniform strain distribution near the interface due to misfit dislocations and threading dislocations. The TDD also becomes higher because the etchfront of Ge reaches areas with high dislocation density near the interface. In the case of selective Ge growth, a slightly lower TDD is observed in smaller windows caused by a weak pattern size dependence on Ge thickness. A significant decrease of TDD of selectively grown Ge is also observed by increasing the Ge thickness. An about 10 times lower TDD at the same Ge thickness is demonstrated by applying a combination of deposition and etching processes during selective Ge growth.     

Removal of stacking faults in Ge grown on Si through nanoscale openings in chemical SiO2

Nucleation and eventual coalescence of Ge islands, grown out of 5 to 7 nm diameter openings in chemical SiO₂ template and epitaxially registered to the underlying Si substrate, have been shown to generate a low density of threading dislocations (?10⁶ cm^− 2). This result compares favorably to a threading dislocation density exceeding 10⁸ cm^− 2 in Ge films grown directly on Si. However, the coalesced Ge film contains a relatively high density of stacking faults (5 × 10⁷ cm^− 2), and subsequent growth of GaAs leads to an adverse root-mean-square roughness of 36 nm and a reduced photoluminescence intensity at 20% compared to GaAs grown on Ge or GaAs substrates. Herein, we find that annealing the Ge islands at 1073 K for 30 min before their coalescence into a contiguous film completely removes the stacking faults. However, the anneal step undesirably desorbs any SiO₂ not covered by existing Ge islands. Further Ge growth results in a threading dislocation density of 5 × 10⁷ cm^− 2, but without any stacking faults. Threading dislocations are believed to result from the later Ge growth on the newly exposed Si where the SiO₂ has desorbed from areas uncovered by Ge islands. The morphology and photoluminescence intensity of GaAs grown on the annealed Ge is comparable to films grown on GaAs or Ge substrates. Despite this improvement, the GaAs films grown on the annealed Ge/Si exhibit a threading dislocation density of 2 × 10⁷ cm^− 2 and a minority carrier lifetime of 67 ps compared to 4 to 5 ns for GaAs on Ge or GaAs substrates. A second oxidation step after the high temperature anneal of the Ge islands is proposed to reconstitute the SiO₂ template and subsequently improve the quality of Ge film.     

Effect of layer thickness on structural quality of Ge epilayers grown directly on Si(001)

A study of Ge epilayer growth directly on a Si(001) substrate is presented, following the two temperature Ge layer method. In an attempt to minimize the overall thickness while maintaining a good quality Ge epilayer, we have investigated the effect of varying the thickness of both the low and high temperature Ge layers, grown at 400 °C and 670 °C, respectively, by reduced pressure chemical vapor deposition. We find that the surface of the low temperature (LT) seed layer has a threading dislocation density (TDD) to the order of 10¹¹ cm^− 2. On increasing the LT layer thickness from 30 nm to 150 nm this TDD decreases by a factor of 2, while its roughness doubles and degree of relaxation increases from 82% to 96%. Growth of the high temperature (HT) layer reduces the TDD level to around 10⁸ cm^− 2, which is also shown to decrease with increasing layer thickness. Both the surface roughness and degree of relaxation reach stable values for which increasing the thickness beyond about 700 nm has no effect. Finally, annealing the HT layer is shown to reduce the TDD, without affecting the degree of relaxation. However, unless a thick structure is used the surface roughness increases significantly on annealing.     

Interfacial reactions in Nb/NbSi2 and Nb/NbSi2-B systems

For the use of Nb-based alloys at high temperatures, a high oxidation resistant coating such as NbSi₂ coating is required. In the present study, to clarify the physico-chemical compatibility between Nb and NbSi₂, the extent of the interfacial reaction and the reaction products were studied at temperatures ranging from 1573 to 1773 K. Growth of the reaction layer formed in the interfacial reactions was caused by the preferential diffusion of Si toward to the Nb side, leading to the formation of a Nb₅Si₃ layer. The growth followed a parabolic rate law, and the growth rate constant was expressed by k_p (m² s⁻¹) = 7.98 × 10⁻¹⁰ exp(−131.84 kJ mol⁻¹/RT). In addition, behavior of boron in the Nb/NbSi₂ interfacial reaction was clarified.     

Epitaxial growth of relaxed germanium layers by reduced pressure chemical vapour deposition on (110) and (111) silicon substrates

The growth of Ge on (110) and (111) oriented Si substrates is of great interest to enhance the mobility of both holes and electrons in complementary metal oxide semiconductor transistors. However, the quality of thick, relaxed Ge layers grown epitaxially on these surfaces is usually much lower than similar layers grown on (100) Si, resulting in both higher defect densities (i.e. threading dislocations and stacking faults) and rougher surfaces. In this work we have investigated the growth of Ge layers on (110) and (111) Si substrates by reduced-pressure chemical vapour deposition using a two temperature process. We have found that the combination of suppressing the Ge seed layer roughness and high temperature post-growth annealing can reduce the rms surface roughness of (110) Ge layers to below 2 nm and the threading dislocation density to below 1 × 10⁷ cm^− 2. Thick (111) Ge layers were found to exhibit a very high density of stacking faults, that could not be reduced by post-growth annealing and a higher rms surface roughness of around 12 nm, which was limited by the Ge seed layer.     

Study on field emission and photoluminescence properties of ZnO/graphene hybrids grown on Si substrates

Zinc oxide/graphene (ZnO/G) hybrids are prepared on n-Si (1 0 0) substrates by electrophoretic deposition and magnetron sputtering technique. The crystal structure, morphology and photoluminescence (PL) properties of the ZnO/G hybrids are analyzed via X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and fluorescence–phosphorescence spectrometer, respectively. The results indicate that the crystal quality of ZnO nanostructure deteriorates after depositing graphene buffer layer. Whereas many three dimensional stacking blowballs form in the ZnO/G hybrid, creating a larger surface area than that of ZnO nanostructure. The photoluminescence (PL) spectrum of the ZnO/G hybrid contains multi-peaks, which are consistent with ZnO nanostructure except for two new peaks at 390 and 618 nm. In addition, field emission measurement reveals that E_to and E_thr decrease from 8.01 V μm⁻¹ and 14.90 V μm⁻¹ of the ZnO nanostructure to 2.72 V μm⁻¹ and 7.70 V μm⁻¹ of the ZnO/G hybrid. ZnO/G hybrid is characteristic of having excellent emitting behavior suitable for application in field emission technology.     

Effect of thin intermediate-layer of InAs quantum dots on the physical properties of InSb films grown on (001) GaAs

In this study the formation of a semiconducting InSb layer, preceded by the growth of an intermediate layer of InAs quantum dots, is attempted on (001) GaAs substrate. From the analysis of atomic-force-microscopy and transmission-electron-microscopy images together with Raman spectra of the InSb films, it is found that there exists a particular layer-thickness of ~ 0.5 μm above which the structural and transport qualities of the film are considerably enhanced. The resultant 2.60-μm-thick InSb layer, grown at the substrate temperature of 400 °C and under the Sb flux of 1.5 × 10^− 6 Torr, shows the electron mobility as high as 67,890 cm²/Vs.     

The effects of low temperature buffer layer on the growth of pure Ge on Si(001)

We investigated the effects of low temperature (LT) Ge buffer layers on the two-step Ge growth by varying the thickness of buffer layers. Whereas the two-step Ge layers using thin (< 40 nm) Ge buffer layers were roughened due to the formation of SiGe alloy, pure and flat Ge layers were grown by using thick (> 50 nm) LT Ge buffer layers. The lowest threading dislocation density of 1.2 × 10⁶ cm⁻² was obtained when 80-nm-thick LT Ge buffer layer was used. We concluded that the minimum thickness of buffer layer was required to grow uniform two-step Ge layers on Si and its quality was subject to the thickness of buffer layer.     

The effect of temperature on toluene sorption by granular activated carbon and its use in permeable reactive barriers in cold regions

Granular activated carbon (GAC) has been used as an adsorbent for hydrocarbons in a range of permeable reactive barriers. This work investigates the influence of temperature on adsorption performance. In particular, the influence of temperature in the range of 20 °C to 4 °C on the sorption equilibrium and kinetics of toluene on GAC surface were investigated. The results show that low temperature leads to decreased toluene sorption by GAC and slower reaction kinetics. Sorption kinetics studies show that diffusion coefficients are also lower at 4 °C (3.65 × 10⁻¹³ m² s⁻¹) than 20 °C (5.112 × 10⁻¹³ m² s⁻¹).     

Co-sputtered oxide thin film encapsulated organic electronic devices with prolonged lifetime

Effective top-side thin film encapsulation for organic light-emitting devices (OLEDs) was achieved by deposition of a multi-layer water diffusion barrier stack to protect the device against moisture permeation. The barrier stack was formed by alternative depositions of co-oxide and fluorocarbon (CF_x) films. The co-oxide layer was fabricated by magnetron co-sputtering of silicon dioxide (SiO₂) and aluminum oxide (Al₂O₃). While the CF_x layer was formed by plasma enhanced chemical vapor deposition. The water vapor transmission rate of the optimized diffusion barrier stack can be down to 10^− 6 g/m²/day. The OLEDs encapsulated with the multilayer stack have been shown to have operation lifetime of over 18,000 h which is nearly the same as devices with conventional glass-cover encapsulation.     

Application of 3D image correlation for full-field transient plate deformation measurements during blast loading

A high-speed stereo-vision system is employed to quantify dynamic material response during buried blast loading. Deformation measurements obtained using 3D image correlation of synchronized, patterned stereo-vision images obtained with an inter-frame time in the range 16 μs ≤ t ≤ 40 μs indicate that (a) buried blast loading initially induces highly localized material response directly under the buried blast location, with severity of the blast event a strong function of depth of explosive burial, (b) for relatively shallow (deep) depth of explosive burial, plate surface velocities and accelerations exceed 220 m s⁻¹ (100 m s⁻¹) and 6 × 10⁶ m s⁻² (1.5 × 10⁶ m s⁻¹) during the first 30 μs (80 μs) after detonation, respectively.     

Honeycomb voids due to ion implantation in germanium

For future semiconductor devices, germanium layers are very attractive due to their high carrier mobility with ion implantation remaining the dominant method for forming pn junctions. Yet, implantation of heavy ions above a critical dose causes inadmissible surface roughness and formation of voids. To understand the main factors of influence, a comprehensive study on void formation was performed with different ions (BF₂, P, Al, Ga, Ge, As, Sb) implanted at various doses, dose rates, and energies. It was found that the dose is the most important parameter for void formation. The critical dose was determined to be 2 · 10¹⁵ cm^− 2 for As, 2 · 10¹⁵ cm^− 2 for Ga, and 5 · 10¹⁴ cm^− 2 for Sb, respectively. For ions with lower mass (BF₂, P, Al), no or only negligible surface roughening was observed.     

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.     

Effect of Sb addition on the tensile deformation behavior of lead-free Sn–3.5Ag solder alloy

Tensile deformation behavior of Sn–3.5Ag and Sn–3.5Ag–1.5Sb alloys was investigated at temperatures ranging from 298 to 400 K, and strain rates ranging from 5 × 10⁻⁴ to 1 × 10⁻² s⁻¹. After melting and casting, the samples were rolled to sheets, from which tensile specimens were punched and pulled to fracture in uniaxial tension tests. Scanning electron microscopy (SEM) was used to study the microstructure and fracture surface of the samples. Addition of 1.5% Sb into the binary alloy resulted in an increase in both ultimate tensile strength (UTS) and ductility. The enhanced strength was attributed to the solid solution hardening effects of Sb in the Sn matrix. The improved ductility was, however, caused by the structural refinement which results in the higher strain rate hardening of the Sb-containing alloy. This was manifested by the higher strain rate sensitivity (SRS) indices (m) of 0.14–0.27, as compared to 0.11–0.20 found for the Sn–3.5Ag alloy.     

Epitaxy of In0.01Ga0.99As on Ge/offcut Si (001) virtual substrate

In_0.01Ga_0.99As thin films free of anti-phase domains were grown on 7° offcut Si (001) substrates using Ge as buffer layers. The Ge layers were grown by ultrahigh vacuum chemical vapor deposition using ‘low/high temperature’ two-step strategy, while the In_0.01Ga_0.99As layers were grown by metal-organic chemical vapor deposition. The etch-pit counting, cross-section and plane-view transmission electron microscopy, room temperature photoluminescence measurements are performed to study the dependence of In_0.01Ga_0.99As quality on the thickness of Ge buffer. The threading dislocation density of Ge layer was found to be inversely proportional to the square root of its thickness. The threading dislocation density of In_0.01Ga_0.99As on 300 nm thick Ge/offcut Si was about 4 × 10⁸ cm^− 2. Higher quality In_0.01Ga_0.99As can be obtained on thicker Ge/offcut Si virtual substrate. We found that the threading dislocations acted as non-radiative recombination centers and deteriorated the luminescence of In_0.01Ga_0.99As remarkably. Secondary ion mass spectrometry measurement indicated as low as 10¹⁶ cm^− 3 Ge unintended doping in In_0.01Ga_0.99As.