Ge Incorporation Research Articles

Atmospheric In situ Arsenic-Doped SiGe Selective Epitaxial Growth for Raised-Extension N-type Metal–Oxide–Semiconductor Field-Effect Transistor

We have investigated the AsH3 and GeH4 flow rate dependences of As concentration and growth rate for atmospheric in situ As-doped SiGe selective epitaxial growth. A high As concentration of 3.2×1019 atoms/cm3 and a high growth rate of 13 nm/min were achieved for Si0.79Ge0.21 selective epitaxial growth. The good selectivity was confirmed, and the epitaxial film showed high crystalline quality, a smooth surface and an abrupt change in the dopant profile at the interface. These results were interpreted in terms of the suppression of As surface segregation and the enhancement of As diffusion due to Ge incorporation in Si growth.

Ion beam synthesis of 4H‐(Si1–xC1–y)Gex +y solid solutions

Abstract4H silicon carbide (Si1–x C1–y )Gex +y solid solutions with an average Ge incorporation on lattice sites ranging from 0.7 to 2.5 percent were formed by ion beam synthesis. RBS and RBS/C investigations revealed a decreasing Ge lattice incorporation with increasing implantation dose above 10%. The carried out rapid thermal annealing at 1300 °C reduces the residual damage, increases the lattice site occupation and led to negligible change in the concentration profiles. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrathin Si capping layer suppresses charge trapping in HfOxNy∕Ge metal-insulator-semiconductor capacitors

In this study the authors investigated the Ge outdiffusion characteristics of HfOxNy∕Ge metal-insulator-semiconductor capacitors to determine their charge trapping behavior. Capping the Ge substrate with an ultrathin Si layer inhibits the incorporation of Ge into the high-k bulk dielectric in the form of GeOx, thereby diminishing the resultant oxide charge trapping. The thermal stability of the entire capacitor structure was also improved after performing an additional Si passivation process.

Effect of Germanium on Solid-Phase Reaction and Effective Work Function in Fully Ni-Germanosilicided $[\hbox{Ni}(\hbox{Si}_{1 - x}\hbox{Ge}_{x})]$ Gate

Fully Ni-germanosilicided [Ni(SiGe)] gate electrode was systematically investigated by means of both structural analyses and electrical measurements. The authors fabricated Ni(SiGe)-gated MOS capacitors with various Ge fractions through the solid-phase reaction at Ni/polycrystalline SiGe (poly-SiGe) interface. It was found that Ge atoms can only be dissolved in NiSi phase, and then Ni(SiGe) phase is formed. In addition, even in the case that the thickness ratio of Ni to Si is equivalent to that required to form Ni2Si, Ge atoms induce phase change from Ni2Si to Ni(SiGe) near SiO2 interface. This phenomenon promotes condensation of Ge atoms in Ni(SiGe). The values of effective work function (Phieff) are independent of the Ge fraction in the low Ge fraction (Ge < 60%) Ni(SiGe) gate. On the contrary, the Phieff values begin to change to values larger than that of NiSi in the case of a Ge fraction higher than 60%. In addition, the Ge incorporation modulates the Phi eff shift effect of piled-up B atoms to the opposite direction compared to the NiSi cases reported previously. As a result, the controllable Phieff range for piled-up B atoms can be expanded to 0.47 eV near the Si midgap

Effect of growth conditions on the composition and structure of Si1−xGex nanowires grown by vapor–liquid–solid growth

The effect of growth conditions on the composition and structure of Si1−xGex nanowires grown by the vapor–liquid–solid method using gaseous precursors (SiH4 and GeH4) was investigated. Transmission electron microscopy was used to characterize the structural properties and elemental composition of the nanowires. At higher growth temperatures (&gt;425 °C), Ge thin film deposition on the nanowire surface resulted in Au loss during growth and the formation of tapered structures. By simultaneously reducing the growth temperature from 425 to 325 °C to suppress the rate of Ge film deposition and increasing the GeH4/(GeH4 + SiH4) gas ratio, Si1−xGex nanowires were produced with Ge fractions spanning the entire composition range. The Ge fraction follows that predicted from the elemental nanowire growth rates in the Ge-rich (x &gt; 0.5) regime, but deviates to higher Ge fractions in Si-rich (x &lt; 0.5) nanowires. A mechanism was proposed whereby surface diffusion provides an additional pathway to Ge incorporation in Si-rich Si1−xGex nanowires.

Improvement of 4H-SiC Selective Epitaxial Growth by VLS Mechanism Using Al and Ge Based Melts

Al-Si and Ge-Si systems were studied for selective epitaxial growth (SEG) of 4H-SiC by the Vapour-Liquid-Solid mechanism. Al-Si and Ge-Si bilayers stackings were deposited on 8° off, Si face, 4H-SiC substrates. After patterning of the layers, the samples were heated up to 1000°C and 1220°C, respectively, for Al-Si and Ge-Si stackings in order to melt the layers. Propane was introduced either during the initial heating ramp, before melting of the alloy, or after reaching the temperature plateau. It was found that introduction of propane before melting was a key parameter in order to improve the homogeneity of the deposit. In both cases, SEG of SiC was achieved. However, the best results were obtained with Ge-Si system giving smooth and uniform ∼100 nm thick epitaxial deposits on all the pattern sizes and shapes. Ge incorporation in the SiC was found to be rather limited but homogeneous in the layer.

Atomic Layer Epitaxy of (Si&lt;sub&gt;1-x&lt;/sub&gt;C&lt;sub&gt;1-y&lt;/sub&gt;)Ge&lt;sub&gt;x+y&lt;/sub&gt; Layers on 4H-SiC

3C-(Si1-xC1-y)Gex+y ternary alloys were grown on 8.5° off axis 4H-SiC substrates by solid source molecular beam epitaxy in a temperature range between 750°C and 950°C. Energy dispersive X-ray (EDX) analysis revealed a decrease of the Ge incorporation versus substrate temperature. This effect is due to the fixed Si/Ge ratio during the epitaxial growth. The Ge distribution within the grown epitaxial layers was found to be nearly homogeneous. The investigations by atomic location by channeling enhanced microanalysis allowed the conclusion that Ge is located mainly at Si lattice sites.

Characterization of a 3C-SiC Single Domain Grown on 6H-SiC(0001) by a Vapor−Liquid−Solid Mechanism

By a vapor−liquid−solid (VLS) mechanism, where a Ge−Si melt is fed by propane, 3C-SiC layers of ∼1.4 μm thickness were grown on 6H-SiC on-axis substrates. These layers were found to be single domain as seen from morphological and electron backscattering diffraction observations. They were free of any hexagonal inclusion. Both transmission electron microscopy and high-resolution X-ray diffraction show the high crystalline quality of the grown material. Nitrogen was found to be the main impurity, at a concentration of (6−7) × 1017 cm-3 as estimated by Raman spectroscopy, though Al contamination was also detected by low-temperature photoluminescence. The identification and the quantification of Ge incorporation inside the SiC layers were determined by particle-induced X-ray emission (PIXE). The Ge concentration was calculated to be 5 × 1018 atoms/cm3.

Influence of alloy composition on carrier transport and solar cell properties of hydrogenated microcrystalline silicon-germanium thin films

The authors report on carrier transport properties and spectral sensitivities of hydrogenated microcrystalline silicon-germanium (μc-Si1−xGex:H) alloys fabricated by low-temperature (∼200°C) plasma-enhanced chemical vapor deposition over the wide compositional range. Hall-effect and conductivity measurements reveal a change from weak n-type to strong p-type conduction for x&amp;gt;0.75 and a monotonic decrease in photoconductivity upon Ge incorporation. In a p-i-n diode structure, the Ge incorporation into i layer reduces quantum efficiencies in the short wavelengths, indicating an increased photocarrier recombination at p∕i interface. Nevertheless, under reverse biased condition, a 0.9-μm-thick μc-Si0.6Ge0.4:H absorber yields a large photocurrent of &amp;gt;27mA∕cm2 (air mass 1.5 global) with spectral sensitivities extending into infrared wavelengths, offering a potential advantage over conventional microcrystalline silicon solar cells.

Influences of Annealing Temperature on Characteristics of Ge p-Channel Metal Oxide Semiconductor Field Effect Transistors with ZrO2 Gate Dielectrics

The dependence of gate leakage current and p+/n-junction characteristics on annealing temperature is investigated comprehensively in order to obtain good electrical characteristics of Ge p-channel metal oxide semiconductor field effect transistors (p-MOSFETs) with ZrO2 gate dielectrics. The upper limit of annealing temperature is restricted to 500 °C to preserve low gate leakage. Gate leakage current remains low even after Ge incorporation into ZrO2, because ZrO2/Ge gate stacks retain their band alignment to as high as 500 °C. The degradation of gate leakage at the high temperature of 700 °C is due to the emergence of void regions near the interface in the Ge substrate. On the other hand, the lower limit of the annealing temperature is restricted to 400 °C in order to activate dopant boron sufficiently. Good rectifying diode characteristics lead to promising p-MOSFET performance, such as an S-factor of 80 mV/decade. The effective hole mobility of the ZrO2/Ge gate stack without an intentional interfacial layer after annealing at the optimized temperature is as high as 100 cm2/(V·s).

Electrical and Structural Properties of Heavily Ge-Doped GaAs Grown by Molecular-Beam Epitaxy

The properties of GaAs highly doped with Ge grown by molecular-beam epitaxy (MBE) and migration-enhanced epitaxy (MEE) have been studied. We report here that, although Ge doped GaAs films grown by conventional MBE at temperatures lower than 450 °C tend to become semi-insulating materials, a conductive Ge-doped GaAs film with an electron concentration as high as 2×1019 cm-3 can be grown even at 300 °C by MEE. In MBE grown samples, a transition from n-type conductivity to p-type conductivity is observed when the Ge concentration of the films exceeds 1×1020 cm-3, whereas in MEE grown layers at 300 °C only n-type conductivity is observed regardless of the Ge concentration. The lattice constants of these MEE-grown samples are much larger than those of MBE-grown samples with equivalent Ge concentrations. These results indicate that Ge incorporation mechanism is quite different in MEE at low temperatures from that at high temperatures. The large lattice constant of as-grown MEE-grown layers suggests that a substantial fraction of Ge atoms occupy interstitial sites and act as donors. Postgrowth annealing results in marked reductions in lattice constant and electron concentration in MEE samples. The resulting lattice constants are even smaller than those of the n- and p-type GaAs films grown by MBE at high temperatures. This observed result can be explained in terms of (GaAs)1-x(Ge2)x alloy formation in MEE samples during annealing.

Microcrystalline silicon–germanium alloys for solar cell application: Growth and material properties

Microcrystalline silicon–germanium (μc-Si1−xGex:H) alloy films have been grown by 100-MHz glow-discharge of a SiH4/GeH4/H2 gas mixture. Alloys over a full range of compositions were prepared to gain a comprehensive understanding of their growth and material properties. With increasing GeH4 concentration in the gas-phase, we observed a preferential Ge incorporation behavior in the solid. Growth rate studies revealed that the Ge incorporation efficiency from source gas to solid is about five times greater than for Si at growth temperature of 200°C, which accounts for the variation of alloy composition. With increasing Ge incorporation in the solid, on the other hand, we find a monotonic decrease in photoconductivity, followed by an electrical transition from weak n-type to strong p-type conduction at x>0.7. At x≈0.4, however, we obtained relatively high photoconductivity gains by a factor of 20 and strong infrared response in the solar cell structure. The Ge incorporation behavior and its effect on charge carrier transport are discussed.

Investigation of the interface manipulation in SiC(100) on Si(100) with isovalent impurities

AbstractSIMS and transmission electron microscopy studies revealed an improvement of the SiC/Si(100) heterostructure properties if isovalent atoms with larger atomic dimensions than Si and C were used to modify the interface. The Ge incorporation at the interface suppresses the outdiffusion of Si from the substrate to the surface of the growing SiC layer and, therefore, impedes surface and interface roughening as well as the formation of voids at the SiC/Si interface. SIMS measurements obtained revealed that Ge remains at SiC/Si interface independently of the predeposited amount on Si(100) substrates. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Deposition phase diagrams for Si1−xGex:H from real time spectroscopic ellipsometry

Phase diagrams have been developed to describe rf plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated silicon–germanium alloys (Si1−xGex:H) on crystalline Si substrates held at 200°C. For a series of three such overlapping diagrams established at different flow ratios G=[GeH4]/{[SiH4]+[GeH4]}, the boundary describing the thickness at which the amorphous-to-(mixed-phase microcrystalline) transition occurs [designated a→(a+μc)] shifts rapidly to higher H2-dilution flow ratio R=[H2]/{[SiH4]+[GeH4]} with increasing G. This demonstrates that Ge incorporation strongly suppresses microcrystallite nucleation from the amorphous phase. For each individual phase diagram of this series, the thickness at which an amorphous regime roughening transition occurs [designated a→a] increases with increasing R right up to the a→(a+μc) boundary. Under wide ranges of deposition conditions, however, the maximum a→a transition thickness decreases rapidly with increasing G for the series of phase diagrams with different ratios G. This decrease is weakest for cathodic PECVD of Si1−xGex:H with a self-bias near −20V, suggesting precursor surface diffusion enhancement under such conditions.

Influence of growth temperature conditions on electric properties of CdTe:Ge crystals

AbstractA model of Ge incorporation into CdTe lattice based on the analysis of temperature influence of post‐growth crystal annealing on CdTe:Ge electric properties is proposed. Ge impurity is mainly placed in Te sublattice in crystals fast cooled from high temperatures. GeTe defect is an acceptor defining the electric and photoelectric properties at T ≤ 290 K. GeCd donors and deep (GeCdVCd)/ acceptors are generated in lesser amount. Long‐term ingot thermal treatment at T &lt; 1090 K causes germanium atom relocalization chiefly into cadmium sublattice. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Germanium incorporation into sponge spicules: Development of a proxy for reconstructing inorganic germanium and silicon concentrations in seawater

Measurements of germanium (Ge) in deep-sea sponge skeletons are presented for sponges collected by dredge and for spicules isolated from a range of deep-sea sediment cores. Germanium to silicon (Si) ratios (Ge / Si sp) for sponge silica ranged between 0.075 and 0.380 μmol/mol, which are much lower than the present-day seawater Ge / Si ratio of 0.7 μmol/mol. A plot of Ge / Si sp versus estimated seawater Ge (and Si) concentration produced a linear relationship with the Ge content of spicules increasing with seawater Ge concentration. Plots of Ge / Si sp versus depth for both dredged sponges and sediment-bound spicules produced oceanic profiles similar to those of dissolved Ge (and Si) concentration. To explain the fractionation seen in the sponge Ge / Si sp data two models are presented. The first model used to interpret the data assumes that sponges only respond to the Ge content of the ambient seawater, implying that, Ge incorporation into sponge silica is independent of the seawater Ge / Si ratio up to a Si concentration of about 100 μmol/L. This model is consistent with the 68Ge uptake results of Davie et al. [E.I. Davie, T.L. Simpson, R. Garonne, Experimental germanium incorporation into siliceous sponge spicules, Biol. Cell 48 (1983) 191–202] for cultured spicules. Their results showed that the incorporation of Ge in sponge silica is only dependent on the Ge concentration of the water in which a sponge is growing. The second model used to explain the data assumes that Ge / Si sp fractionation results from subtle differences in the uptake kinetics of Ge and Si. While the assumptions used by each model to describe the data are different, it is possible to use sponge Ge / Si sp data to reconstruct palaeo-Ge concentrations using model I, and to reconstruct palaeo-Si concentrations using both models. Palaeo-Si concentrations estimated using both models are in good agreement.

Germanium Incorporation in HfO2 Dielectric on Germanium Substrate

It is widely reported that a significant amount of germanium is incorporated in gate dielectric during the formation of high-κ gate stack on germanium substrate. In this paper, the dependences of germanium incorporation in on dielectric deposition method, annealing temperature, and annealing ambient were extensively studied by physical methods such as time-of-flight secondary ion mass spectroscopy. The results indicate that the high thermal budget of processes, including deposition and annealing, is the most critical factor to the Ge incorporation. The Ge incorporation in is identified by two mechanisms: Ge atoms out-diffusion from substrate and gaseous GeO diffusion downward into via airborne transportation in the chamber.

Silicon-germanium films deposited by low-frequency plasma-enhanced chemical vapor deposition: Effect of H2 and Ar dilution

We have studied structure and electrical properties of Si1−YGeY:H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y = 0 to Y = 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H2. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y = 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity γ-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.

Kinetics of SiGe chemical vapor deposition from chloride precursors

The paper represents the results of analysis of SiGe growth in a wide range of the growth conditions based on the experimental data on SiGe chemical vapor deposition in different reactor systems. The deposition mechanisms are explained using an original model of the growth kinetics. The effects of the temperature and precursor flow rates on SiGe composition and growth rate are discussed in detail. It is shown that an increase of the growth rate due to the Ge incorporation can be fairly noticeable but it takes place only at low temperatures. Ge concentration in SiGe decreases at high temperatures due to both kinetic and thermodynamic reasons. Effect of the germanium precursor type on the growth rate and alloy composition is also reported.

Hetero-epitaxial growth of SiCGe on SiC

SiCGe/SiC heterojunction structure is required in development of SiC optoelectronic devices and light-activated switching devices. We present in this paper a primary attempt to grow the ternary alloy SiCGe on SiC substrates under varied growth conditions in a conventional hot-wall CVD system. SiH 4, GeH 4 and C 3H 8 were employed as silicon, germanium and carbon sources, respectively. The samples were measured by means of SEM, XPS, XRD, optical absorption, etc. Two different growth modes i.e., island growth and porous growth were observed. It has been shown that germanium atoms can be effectively incorporated into the ternary alloys, which makes their optical gaps to be narrowed with increasing Ge content. However, incorporation of Ge induces a heavy lattice mismatch, which limits the film thickness by the formation of mismatch defects. It has been shown that use of a buffer layer can effectively improve the growth quality of the ternary alloy.