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We fabricated nanocrystalline Ge films using radio-frequency (RF) magnetron plasma sputtering deposition under a high Ar-gas pressure. The Ge nanograins changed from amorphous to crystalline when the distance between the Ge sputtering target and the substrate was decreased to 5 mm and the RF input power was 11.8 W/cm2 (60 W), where the deposition rate was as high as 660 nm/min. In addition, the size of the nanocrystalline grains increased from 100 to 307 nm when the RF input power for plasma production was increased from 11.8 W/cm2 (60 W) to 17.7 W/cm2 (90 W). In the developed narrow-gap plasma process at sub-Torr pressures, nanocrystalline Ge films were successfully fabricated on Cu substrates at low temperatures, without the substrate being heated. However, when annealing was conducted under an N2 atmosphere, which is the conventional method to induce solid-phase crystallization, the amorphous Ge layer on a Cu substrate changed to a Cu3Ge crystal layer through interdiffusion of Ge and Cu atoms at 400–500 °C.

The HfxZryO2 with high Zr content is demonstrated to form the anti-ferroelectric tetragonal phase (AFE t-phase). The peak dielectric constant (47) of Hf0.2Zr0.8O2 is achieved. By taking advantage of the high dielectric constant, the Hf0.2Zr0.8O2 is used in the gate stack on the high mobility Ge0.98Si0.02 channel to significantly enhance the drive current. Stacked two Ge0.98Si0.02 gate-all-around nanowires can have high ION per perimeter of $740~\mu \text{A}/\mu $ m at $\mathrm{V}_{\mathrm{OV}}= \mathrm{V}_{\mathrm{DS}}= 0.5\text{V}$. The thermal budget is as low as 450 °C. [ABSTRACT FROM AUTHOR]

A novel TreeFET architecture as a combination of stacked nanosheets and additional fin interbridges between nanosheets can enhance ION per footprint. The straight sidewalls of interbridges requires {110} sidewalls, which can be fabricated using n+ Ge/Ge0.95Si0.05/Ge epitaxial layers with co-optimization of wet etching. The TreeFET with {110} interbridges has ION per footprint of $870~\mu \text{A}/\mu \text{m}$ at VOV=VDS=0.5V (2.1X of the referenced 3 stacked nanosheets). To minimize the impurity scattering in the interbridges, the 400 °C annealing is used to drive phosphorus in interbridges into the nanosheets, while the low source/drain resistance is still maintained. The increasing ION down to 77 K indicates that the phonon scattering dominates, and the impurity scattering is minimized in the interbridge channels. [ABSTRACT FROM AUTHOR]

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-μm-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under −3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands.

The eight stacked Ge0.75Si0.25 nanosheets, the seven stacked Ge0.95Si0.05 nanowires, and the six stacked Ge0.95Si0.05 nanowires without parasitic channels are demonstrated. These highly stacked channels are made from 18 epilayers consisting of a Ge buffer, nine heavily P-doped Ge sacrificial layers, and eight GeSi channel layers with the low growth temperature (350 °C and 375 °C) to ensure the entire epilayers metastable without dislocations in the channels. The isotropic wet etching by H2O2 and NH4OH + H2O2 is used for the channel release and the removal of the parasitic channels, respectively. The delicate interplay between epilayer design and wet etching is implemented to fabricate the highly stacked GeSi channels. High inter-channel uniformity of the eight stacked Ge0.75Si0.25 nanosheets is obtained due to the superior etching selectivity. High ${I}_{\mathrm{\scriptscriptstyle ON}}$ per stack and per footprint of the seven stacked Ge0.95Si0.05 nanowires and the six stacked Ge0.95Si0.05 nanowires without parasitic channels are achieved due to the high mobility ${L}_{4}$ valleys and nanowire conduction. The reduced subthreshold slope (SS) and improved ${I}_{\mathrm{\scriptscriptstyle ON}} / {I}_{\mathrm{\scriptscriptstyle OFF}}$ are obtained by parasitic channel removal. The record ${I}_{\mathrm{\scriptscriptstyle ON}}$ of $120~\boldsymbol \mu \text{A}$ per stack ($4600~\boldsymbol \mu \text{A} / \boldsymbol \mu \text{m}$ per channel footprint) at ${V}_{\mathrm{\scriptscriptstyle OV}} = {V}_{\mathrm{\scriptscriptstyle DS}} = 0.5$ V is reached among reported Ge/GeSi 3-D nFETs. [ABSTRACT FROM AUTHOR]

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-μm-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under −3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands. [ABSTRACT FROM AUTHOR]

We present a detailed study on fabrication and characterization of Ge/GeSn heterojunction p-type tunnel-field-effect-transistors (TFETs). Critical process modules as high-k stack and p-i-n diodes are addressed individually. As a result an ultrathin equivalent oxide thickness of 0.84 nm with an accumulation capacitance of 3~\mu \textF /cm2 was achieved on an extremely scaled tri-layer stack of GeSnOx/Al2O3/HfO2 deposited by atomic-layer deposition monitored in situ by spectroscopic ellipsometry. Combining these process modules, Ge/GeSn heterojunction pTFETs are fabricated and characterized to demonstrate the best in-class pTFET performance in the GeSn material system. The transfer characteristics of the TFETs show signatures of the trap-assisted thermal generation in the subthreshold regime which is explained by a modified Shockley–Read–Hall model. For the ON-state current, we used band-to-band tunneling models calculated using parameters from the density functional theory. We then use the calibrated model to project performance of GeSn pTFETs with increased Sn content (lower bandgap), reduced trap density and ultrathin body geometry. Both experimental and projected results are benchmarked against state-of-the art III–V (e.g., In0.65Ga0.35/GaAs0.4Sb0.6) pTFETs. We demonstrate the ability of GeSn to achieve superior performance with both high ON-current and sub-60mV/decade switching benefiting from the small and direct bandgap for higher Sn contents. [ABSTRACT FROM PUBLISHER]

To satisfy the growing market demand for embedded nonvolatile memory, alternative solutions to Flash technology are currently under investigation. Among these, phase change memory (PCM) is attracting strong interest due to the low cost of integration with the CMOS front-end and good scalability. Embedded PCM, however, must feature high reliability during both packaging and functional stages. This paper studies reliability of PCM based on Ge-rich GeSbTe, providing evidence for resistance drift and decay in both the reset and set states. Set-state instability is attributed to grain-boundary relaxation and grain growth. A unified model is presented, capable of predicting the reliability of set/reset states at elevated temperature. [ABSTRACT FROM AUTHOR]

In this paper, we examine the problem of the drift of the low-resistance state (LRS) in phase change memories based on C or N doped and undoped Ge-rich Ge2Sb2Te5 . A novel procedure, named R–SET technique, is proposed to boost the SET speed of these innovative phase change materials by overcoming the decrease of crystallization speed caused by Ge enrichment. The R–SET technique allows, at the same time, an optimized SET programming of the memory cell and the reduction of the LRS drift with respect to standard SET procedures. A circuit that generates the desired R–SET pulse based on a time reference scheme is proposed and discussed. [ABSTRACT FROM PUBLISHER]

The potential of rupture-oxide mushroom phase-change memory cells is assessed through 2-D finite element analysis using electro-thermal models with temperature-dependent material parameters, coupled with a circuit model for access transistors. The mushroom cell structure used for the simulations consists of a 100-nm thick Ge2Sb2Te5 layer separated from a 20-nm wide TiN bottom heater by a 3-nm thick SiO2 rupture-oxide layer. The ruptured oxide is modeled as a conductive filament through the oxide layer at the center of the heater. The effects of supply voltage, gate voltage, access transistor width, filament diameter and resistivity are studied using a read/reset/read sequence enabled by a dynamic amorphization model. The simulation results show that rupture-oxide cells can be operated with smaller voltages, currents and transistor widths compared to their conventional counterparts for the same resistance contrast. Moreover, it is shown that the cell performance is further improved for narrower and more resistive filaments. [ABSTRACT FROM AUTHOR]

Segmented-channel \Si1 - x\Gex/\Si p-channel MOSFETs are fabricated using a conventional process, starting with corrugated \Si1 - x\Gex/\Si substrates. As compared with the control devices fabricated using the same process but starting with a noncorrugated \Si1 - x\Gex/\Si substrate, the segmented-channel MOSFETs show better layout efficiency (30% higher ION for IOFF = \10\ \nA per micrometer layout width) due to enhanced hole mobility and dramatically reduced dependence of performance on layout width due to the geometrical regularity of the channel region. [ABSTRACT FROM AUTHOR]

We propose and analyze a strain-balanced GezSn1-z\--SixGeySn1-x-y multiple-quantum-well (MQW) laser. By incorporating a proper amount of \alpha-Sn into Ge, a direct-bandgap GeSn alloy can be realized to achieve population inversion in the direct conduction band. The introduction of compressive strain into the GeSn QW can effectively modify the valence band structure to reduce the threshold carrier density. We calculate the electronic band structure and the polarization-dependent optical gain of the strained GezSn1-z\--SixGeySn1-x-y MQW laser taking into account the effect of the L-conduction bands. We also present our waveguide design for index guidance and calculate the optical confinement factors of various regions. Our calculation indicates that the modal gain can reach the threshold condition and lead to lasing action. [ABSTRACT FROM PUBLISHER]

Temperature dependent magnetoelastic properties of Fe100-xGex(5 < x < 18) single crystals have been measured. Tetragonal magnetostriction (3/2)λ100 measurements at x = 5.7, 12.1, 14.9, and 17.7 were performed between 78 K and 426 K and resonant ultrasound spectroscopy measurements were used to determine the shear elastic constant c' from S K to 300 K for x = 6.4, 7.2, 10.8, 14.6, 17.7, and 17.9. A clear distinction was observed between the temperature dependencies of λ100 for the A2 and D03 phases of Fe100-xGex. The elastic constant c' displays a monotonic decrease with concentration through the different phases (6 < × < 18) and at all temperatures. Experimental values of the tetragonal magnetoelastic coupling constant -b1 at 81 K were remarkably consistent with theoretical values determined by density functional calculations at 0 K. [ABSTRACT FROM AUTHOR]

We investigate the relationship between electronics and geometry in a nonplanar SiGe/Si resonant quantum cavity (RQC) subject to a magnetic field. The transfer matrix technique originally due to Usuki et al. [Phys. Rev. B, vol. 52, pp. 8244-8255, 1995] has been modified to account for the nonzero local curvature of the RQC. Our results demonstrate that low-temperature ballistic magnetoconductance in nonplanar RQCs is highly sensitive to the changes in curvature for a wide range of magnetic field strengths. [ABSTRACT FROM PUBLISHER]

In this paper, Ge the comeback semiconductor material is discussed. It is used as an enabling material for the next generation of device technology primarily due to its high carrier mobility. Ge, along with other high-mobility such as III/V compounds, are projected to be the the new range of semiconductor material. The technology for the growth of Ge and (In) GaAs active areas on an Si substrate must be developed [ABSTRACT FROM PUBLISHER]

A theoretical study of the write, read, and erase processes in electrical scanning probe storage on phase-change media is presented. Electrical, thermal, and phase-transformation mechanisms are considered to produce a physically realistic description of this new approach to ultrahigh-density data storage. Models developed are applied to the design of a suitable storage layer stack with the necessary electrical, thermal, and tribological properties to support recorded bits of nanometric scale. The detailed structure of nanoscale crystalline and amorphous bits is also predicted. For an optimized trilayer stack comprising Ge2Sb2Te5 sandwiched by amorphous or diamond-like carbon layers, crystalline bits were roughly trapezoidal in shape while amorphous bits were semi-ellipsoidal. In both cases, the energy required to write individual bits was very low (of the order of a few hundred picoJoules). Amorphous marks could be directly overwritten (erased), but crystalline bits could not. Readout performance was investigated by calculating the readout current as the tip scanned over isolated bits and bit patterns of increasing density. The highest readout contrast was generated by isolated crystalline bits in an amorphous matrix, but the narrowest readout pulses arose from isolated amorphous marks in a crystalline background. To assess the ultimate density capability of electrical probe recording the role of write-induced intersymbol interference and the thermodynamic stability of nanoscale marks were also studied. [ABSTRACT FROM PUBLISHER]

We report on the fabrication and characterization of nanoscale memory elements based on solid electrolytes. When combined with silver, chalcogenide glasses such as Se-rich Ge-Se are good solid electrolytes, exhibiting high Ag ion mobility and availability. By placing an anode that has oxidizable Ag and an inert cathode (e.g., Ni) in contact with a thin layer of such a material, a device is formed that has an intrinsically high resistance, but which can be switched to a low-resistance state at small voltage via reduction of the silver ions. An opposite bias will return the device to a high-resistance state, and this reversible switching effect is the basis of programmable metallization cell technology. In this paper, electron beam lithography was used to make sub-100-nm openings in polymethylmethacrylate layers used as the dielectric between the device electrodes. The solid electrolyte film was formed in these via-holes so that their small diameter defined the active switching area between the electrodes. The Ag-Ge-Se electrolyte was created by the photodiffusion, with or without thermal assistance, of an Ag layer into the Ge-Se base glass. Combined thermal and photodiffusion leads to a nanophase separated material with a dispersed Ag ion-rich material with an average crystallite size of 7.5 nm in a glassy insulating Ge-rich continuous phase. The nanoscale devices write at an applied bias as low as 0.2 V, erase by -0.5 V, and fall from over 107 Ω to a low-resistance state (e.g., 104 Ω for a 10-μA programming current) in less than 100 ns. Cycling appears excellent with projected endurance well beyond 1011 cycles. [ABSTRACT FROM PUBLISHER]

Large-area Si/Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors (HBTs) have been demonstrated with record output power at S-Band. Under pulsed conditions in class C operation, a saturated power in excess of 230 W was achieved at 2.8 GHz. At 200 W the devices exhibited a collector efficiency of 46% and a power gain of 6.9 dB. Devices with implanted Si bases had comparable gain, but only 35% efficiency at 150 W, and saturated at 180 W. In class A operation, 13.5 dB gain was demonstrated at 3.1 GHz on smaller devices. For high f/sub max/, a self-aligned silicided polysilicon-emitter structure was used in conjunction with a graded Si/sub 1-x/Ge/sub x/ base. Variable temperature dc tests and accelerated life tests have indicated no reliability problems. The results indicate for the first time that Si/SiGe HBTs are suitable for high-power, high-frequency applications. [ABSTRACT FROM AUTHOR]

We report on quantitative strain measurement of a Si1−xGex-channel-transistor performed using the scanning moiré fringes that appear in high-angle annular dark-field scanning transmission electron microscopy. The strain fields in the Si1−xGex-channel region were measured along three orthogonal axes (X, Y, and Z). This three-axis strain measurement enabled us to calculate the stress applied in the channel region of the transistor, which was \(\sigma _{xx}=-4.3\) GPa, \(\sigma _{yy}=-2.8\) GPa, and \(\sigma _{zz}=- 1.5\) GPa for the longitudinal, transverse, and vertical directions relative to the current flow, respectively. The three-axis stress analysis demonstrated in this letter will enable comprehensive understanding of the strain engineering in electronic devices. [ABSTRACT FROM AUTHOR]

A 40-GHz monolithic mode-locked laser diode integrated with a tensile-strained multiple-quantum-well saturable absorber was developed for the purpose of polarization-insensitive all-optical clock recovery in a single chip of a semiconductor device. Clock recovery with small polarization sensitivity less than 0.2 dB was successfully achieved. We also demonstrated a stable clock recovery from polarization-scrambled data signals. [ABSTRACT FROM PUBLISHER]

A novel hybrid distributed Bragg reflector (DBR) consisting of a substrate-independent amorphous Si-Al-oxide stack and a Cr-Au-Ni-AuGe metallic bonding layer is developed for optoelectronic applications. The metal layers serve as a high-reflectance mirror as well as an adhesion material used in wafer bonding. The hybrid DBR utilizing the reflective metals can achieve a reflectivity of above 99.95% in merely six periods. In addition, the hybrid DBR can adjoin heterogeneous materials at a low temperature of 320°C using a simple metallic bonding process. The hybrid DBR has been successfully applied to the fabrication of 1.55-μm GaInAsP-InP vertical-cavity surface-emitting laser cavities on Si substrates. [ABSTRACT FROM PUBLISHER]

Fe/sub x/Ge/sub 100-x/ films with compositions in the range 50/spl les/x/spl les/82 at 300 K were deposited by rf diode, sequential sputtering from elemental targets. All the films were amorphous at 300 K indicating that the Fe concentration in the stable amorphous films was increased by more than 10 at. % over that obtained by vapor deposition. The sequentially sputtered Fe-Ge films exhibited a heteroamorphous morphology with nanoscale features that varied with composition. The variations in the 4/spl pi/M/sub s/ and T/sub c/ for the sputtered Fe rich films, agreed well with data extrapolated from measurements on Ge rich evaporated films. The improvement in the soft magnetic properties produced in these films by rotating magnetic field annealing (RFA) was shown to be correlated with changes in film morphology. [ABSTRACT FROM PUBLISHER]