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This work presents a novel method to introduce a sustainable biaxial tensile strain larger than 1% in a thin Ge membrane using a stressor layer integrated on a Si substrate. Raman spectroscopy confirms 1.13% strain and photoluminescence shows a direct band gap reduction of 100meV with enhanced light emission efficiency. Simulation results predict that a combination of 1.1% strain and heavy n(+) doping reduces the required injected carrier density for population inversion by over a factor of 60. We also present the first highly strained Ge photodetector, showing an excellent responsivity well beyond 1.6um.

Transistors based on III-V semiconductor materials have been used for a variety of analog and high frequency applications driven by the high electron mobilities in III-V materials. On the other hand, the hole mobility in III-V materials has always lagged compared to group-IV semiconductors such as germanium. In this paper, we explore the use of strain and heterostructure design guided by bandstructure modeling to enhance the hole mobility in III-V materials. Parameters such as strain, valence band offset, effective masses, and splitting between the light and heavy hole bands that are important for optimizing hole transport are measured quantitatively using various experimental techniques. A peak Hall mobility for the holes of 960 cm2/Vs is demonstrated and the high hole mobility is maintained even at high sheet charge. [ABSTRACT FROM AUTHOR]

We have studied the surface cleaning of Sb-based compound semiconductors using HF, NH4OH, and HCl cleans and the metal-oxide-semiconductor (MOS) capacitors fabricated subsequently. GaSb, InGaSb, and AlGaSb surfaces are investigated using low-energy radiation from the synchrotron. Capacitance-voltage (C-V) and photoluminescence measurements are carried out on capacitors made with Al2O3 from atomic layer deposition and corroborated with the results from synchrotron spectroscopy. Excellent C-V characteristics with a mid-band-gap interface state density of 3 × 1011/cm2eV are obtained on samples with the HCl clean. This is consistent with the finding that only the HCl acid clean is able to remove the native oxides present on GaSb and InGaSb surfaces, and produce clean and stable surfaces suitable for MOSFET development. Complete removal of AlOx on the AlGaSb surface was not possible using chemical cleaning. Termination of AlGaSb with two monolayers of GaSb is proposed as a solution. [ABSTRACT FROM AUTHOR]

III-V semiconductor field effect transistors require an insulator/channel interface with a low density of electrically active defects and a minimal interface dipole to avoid Fermi level pinning. We demonstrate that an atomically abrupt and unpinned interface can be formed between an In0.53Ga0.47As (100) channel and an Al2O3 dielectric layer grown by atomic layer deposition (ALD) when oxidation of the substrate surface is prevented before and during oxide deposition. X-ray photoelectron spectra and electron microscopy indicate that in situ desorption of a protective As2 layer on the In0.53Ga0.47As (100)-4×2 surface followed by ALD of Al2O3 produced an atomically abrupt interface without Fermi level pinning. Temperature-dependent and frequency-dependent capacitance-voltage and conductance-voltage analysis of the resulting Pt/Al2O3/InGaAs capacitors are consistent with movement of the Fermi level through the InGaAs band gap. Moreover, the nearly ideal flat band voltages observed for gate metals of widely varying work function indicate a small oxide/semiconductor interface dipole. Density functional theory calculations of the electronic structure of an ideal amorphous Al2O3/InGaAs (100) interface predict a weak perturbation of the InGaAs electronic structure if its oxidation is avoided, consistent with experiment. [ABSTRACT FROM AUTHOR]

We demonstrate the Schottky behavior of single-walled carbon nanotube (CNT) film contacts on GaAs by fabricating and characterizing metal-semiconductor-metal (MSM) photodetectors with CNT film electrodes. We extract the Schottky barrier height of CNT film contacts on GaAs by measuring the dark I-V characteristics as a function of temperature. The results show that at temperatures above ∼260 K, thermionic emission of electrons with a barrier height of ∼0.54 eV is the dominant transport mechanism in CNT film–GaAs junctions, whereas at lower temperatures, tunneling begins to dominate suggested by the weak dependence of current on temperature. Assuming an ideal MS diode, this barrier height corresponds to a CNT film workfunction of ∼4.6 eV, which is in excellent agreement with the previously reported values. Furthermore, we characterize the effect of device geometry on the dark current and find that dark currents of the MSM devices scale rationally with device geometry, such as the device active area, finger width, and finger spacing. Finally, we compare the dark and photocurrent of the CNT film-based MSM photodetectors with standard metal-based MSMs. We find that MSM devices with CNT film electrodes exhibit a higher photocurrent-to-dark current ratio while maintaining a comparable responsivity relative to metal control devices. These results not only provide valuable information about the fundamental properties of the CNT film–GaAs interface but also open up the possibility of integrating CNT films as transparent and conductive Schottky electrodes in conventional semiconductor electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

An ultrathin zirconia gate dielectric had been successfully incorporated into germanium metal-oxide-semiconductor (MOS) devices demonstrating very high-permittivity gate stacks with no apparent interfacial layer. In this study, synchrotron-radiation photoemission spectroscopy has been applied on the same gate stack to identify and quantify the presence of any interfacial germanium suboxide layer. By taking progressive core-level spectra during the layer-by-layer removal of the zirconia film, an oxidized germanium layer with submonolayer thickness was found, possibly arising from an interfacial Zr–O–Ge bonding configuration. In addition, the offsets in the valence-band spectra were also monitored and the energy-band diagram of the zirconia–germanium heterostructure was constructed. Compared to high-κ gate stacks on Si, the thinner interfacial layer and larger conduction-band offset in high-κ gate stacks on Ge suggest better scalability towards an ultimately higher MOS gate capacitance. [ABSTRACT FROM AUTHOR]

High-k metal oxide gate dielectrics may be required to extend Moore’s law of semiconductor device density scaling into the future. However, growth of a thin SiO2-containing interface layer is almost unavoidable during the deposition of metal oxide films onto Si substrates. This limits the scaling benefits of incorporating high-k dielectrics in future transistors. A promising approach, in which oxygen-gettering metal overlayers are used to engineer the thickness of the SiO2-based interface layer between metal oxide and Si substrate after deposition of the metal oxide layer, is reported. Using a Ti overlayer with high solubility for oxygen on ZrO2 or HfO2 dielectrics, the effective removal of the low-k interface layer at 300 K has been confirmed by electron microscopy and spectroscopy techniques. Significant enhancement of the gate capacitance density, while retaining low leakage current densities, has also been demonstrated for these interface-engineered high-k gate stacks. [ABSTRACT FROM AUTHOR]

Presents a study that focused on the increasing cost and complexity of semiconductor process development which led to the widespread use of multidimensional semiconductor process simulators. Use of Raman spectroscopy; Background on integrated circuit technologies; Importance of silicon nitride films tp the semiconductor industry.

This work presents titanium oxide (TiOx) and nickel oxide (NiOx) as promising carrier-selective interlayer materials for metal-interlayer–semiconductor contacts for silicon solar cells. The electron-conducting, hole-blocking behavior of TiOx and the opposite carrier-selective behavior of NiOx are investigated using the transmission-line-method. The Fermi level depinning effect and the tunneling resistance are demonstrated to be dependent on the interlayer oxide thickness and annealing temperature. NiOx is furthermore experimentally demonstrated to be capable of improving the effective minority carrier lifetime by quasi-steady-state photoconductance method. Our study demonstrates that TiOx and NiOx can be effective carrier-selective materials for Si solar cells and provides a framework for characterizing carrier-selective contacts. [ABSTRACT FROM AUTHOR]

As Si-transistor technology advances beyond the 10 nm node, the device research community is increasingly looking into the possibility of replacing Si with novel, high mobility materials as the transistor channel. Among several possible candidate materials, germanium and germanium-tin alloys (GeSn) have emerged as strong contenders for the next generation of complementary metal oxide semiconductor (CMOS) transistors. This article presents a comprehensive overview of the state of the art in Ge and GeSn transistor research. We address several key material challenges involved in fabricating high-performance Ge/GeSn-based CMOS transistors, such as gate stack formation and achieving low-resistance contacts to transistor source/drain regions. Using Ge/GeSn as channel materials, we present a FinFET-based, Si-compatible CMOS solution for device dimensions expected in the 7 nm technology node, discuss the practical challenges involved in realizing this design, and highlight directions for future research. [ABSTRACT FROM AUTHOR]

GeSn is quickly emerging as a potential candidate for high performance Si-compatible transistor technology. Fabrication of high-ĸ gate stacks on GeSn with good interface properties is essential for realizing high performance field effect transistors based on this material system. We demonstrate an effective surface passivation scheme for n-Ge0.97Sn0.03 alloy using atomic layer deposition (ALD) of Al2O3. The effect of pre-ALD wet chemical surface treatment is analyzed and shown to be critical in obtaining a good quality interface between GeSn and Al2O3. Using proper surface pre-treatment, mid-gap trap density for the Al2O3/GeSn interface of the order of 1012 cm-2 has been achieved. [ABSTRACT FROM AUTHOR]

We demonstrate room-temperature electroluminescence (EL) from light-emitting diodes (LEDs) on highly strained germanium (Ge) membranes. An external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction. Electrical measurements show an on-off ratio increase of one order of magnitude in membrane LEDs compared to bulk. The EL spectrum from the 0.76% strained Ge LED shows a 100 nm redshift of the center wavelength because of the strain-induced direct band gap reduction. Finally, using tight-binding and finite-difference time domain simulations, we discuss the implications for highly efficient Ge lasers. [ABSTRACT FROM AUTHOR]

Recently, the insertion of ultrathin insulators to form metal-insulator-semiconductor (MIS) contacts has been used extensively to reduce the Schottky barrier height and to shift the Fermi level pinning. In this paper, we investigate the physical non-idealities of the ultrathin insulator in Al/Al2O3/n-GaAs MIS through stoichiometry, density, and bandgap measurements. These structural non-idealities electrically manifest as bulk and interface fixed charges that are found to contribute to the observed barrier height reduction. The effect of fixed charge has not been considered before, and when combined with the previously reported interface dipoles, it provides a more thorough understanding of the MIS contacts. [ABSTRACT FROM AUTHOR]

A transfer matrix method for simulating spin injection into semiconductors in the case of high electric fields has been developed. The nonlinear relationship between electron spin density and electrochemical potential splitting, the effect of electric field on spin diffusion lengths, and spin polarized drift current are accounted for. Using this approach, high magnetoresistance (MR) at high electric fields is predicted. This is due to spin accumulation reaching its extreme values for fermion statistics. This effect opens up a new direction for solving the problem of low MR that semiconductor spintronic devices are facing. [ABSTRACT FROM AUTHOR]

A novel contact technique to reduce the effective Schottky barrier height on Ge and III–V high mobility semiconductors is described. Single metals are used in combination with an ultrathin dielectric to tune the metal/semiconductor barrier height toward zero by shifting or suppressing the strong Fermi-level pinning. Barrier height reduction in the metal-insulator-semiconductor (MIS) contact structure is verified through direct measurements and deduced from increased diode current and reduced contact resistance. Current demonstrations of the MIS contact have barriers as low as 0.05 eV for Er/SiN/n-Ge and 0.18 eV for Al/Al2O3/n-GaAs. The underlying physics is discussed along with the dependence of the minimum achievable contact resistance and barrier height on the metal, dielectric material, dielectric thickness, and substrate doping. For Ge, the MIS contact provides a possible solution to the low n-type Ge dopant solubility problem and allows for the fabrication of Schottky barrier field-effect transistors. For III–V semiconductors, the MIS contact allows for the use of a non-alloyed contact that is crucial for the scalability of III–V metal oxide semiconductor field-effect transistors. [ABSTRACT FROM AUTHOR]

Ge channel is one of the promising performance boosters for replacing Si channel in future complementary metal-oxide-semiconductor technology. The uniaxial stress technology can further enhance the performance of Ge MOSFETs. In this paper, the uniaxial stress effect on Ge NMOSFETs was experimentally and theoretically investigated. The gate dielectric in the Ge NMOSFETs was fabricated by using the novel radical oxidation technique. The high quality of the gate dielectric allowed high vertical field mobilitymeasurements. By applying mechanical uniaxial stress on the fabricated Ge NMOSFETs, the mobility enhancement was experimentally obtained. The physical mechanism of mobility enhancement under such strain indicates that the device performance of Ge NMOSFETs in the ballistic transport regime can achieve as much as 48% drive current gain beyond the 15 nm technology node. [ABSTRACT FROM AUTHOR]

To increase complementary metal oxide semiconductor (CMOS) device performance, new materials are introduced in the gate stack (high-k dielectrics and metal gates) and the transistor channel (Ge, Ill-V materials). In this work we study the atomic layer deposition (ALD) of hafnium oxide on Ge and GaAs substrates. Passivation layers are required to achieve a sufficiently low interface state density, but these might also influence the growth behavior and dielectric quality. Therefore, we investigate the effect of surface preparation, for example, native oxide, wet clean, thermal oxidation, and S-passivation. for the HfCI4/H2O and tetrakis diethylamino hafnium = ((C2H2)2N)2Hf (TDEAH)/H2O processes. The growth of HfO2 from initial submonolayer coverage to continuous HfO2 film is studied by means of Rutherford backscattering, static time-of-flight secondary ion mass spectroscopy, and X-ray photoelectron spectroscopy. HfCl4/H2O ALD depends on the surface preparation. The growth is enhanced on oxide surfaces (thermally grown GeO2, HF-cleaned Ge, and GaOx-AsOy) and inhibited on oxide-free substrates (HBr-cleaned Ge). The initial island growth regime is least pronounced on germanium oxide. In contrast, TDEAH/H2O ALD is independent of the surface preparation. The growth is inhibited in the first ∼20 cycles on native oxide and S-passivated GaAs [(NH4)2S treatment], but the initial island growth regime is quickly followed by the two-dimensional growth regime. [ABSTRACT FROM AUTHOR]

Correlations among interface properties and chemical bonding characteristics in HfO2/GeOrNy/Ge metal-insulator-semiconductor stacks were investigated using in situ remote nitridation of the Ge(100) surface prior to HfO2 atomic layer deposition. Ultrathin (~ 1.1 nm), thermally stable, and aqueous etch-resistant GeOxNy interface layers that exhibited Ge core-level photoelectron spectra similar to stoichiometric Ge3N4 were synthesized. To evaluate GeOxNy/Ge interface defects, the density of interface states (Dit) was extracted by the conductance method across the bandgap. Forming gas annealed (FGA) samples exhibited substantially lower Dit (- l X 1012 cm-2 eV-1) than did high-vacuum-annealed and inert gas anneal samples (- I X 1013 cm-2 eV-1). Gerrnanium core-level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO2 film surface and apparent modification of chemical bonding at the GeOxNy/Ge interface which is related to the reduced Dit. [ABSTRACT FROM AUTHOR]

"Conventional" techniques and related capacitance-voltage characteristic interpretation were established to evaluate interface trap density on Si substrates. We show that blindly applying these techniques on alternative substrates can lead to incorrect conclusions. It is possible to both under- and overestimate the interface trap density by more than an order of magnitude. Pitfalls jeopardizing capacitance- and conductance-voltage characteristic interpretation for alternative semiconductor MOS are elaborated. We show how the conductance method, the most reliable and widely used interface trap density extraction method for Si, can be adapted and made reliable for alternative semiconductors while maintaining its simplicity. [ABSTRACT FROM AUTHOR]

We propose a novel semiconductor optoelectronic (OE) switch that is a fusion of a Ge optical detector and a Si metal-oxide-semiconductor (MOS) field-effect transistor (FET). The device operation principle is investigated, and the performance is explored by simulations. The proof of principle is demonstrated by experiments. The use of Ge enables operation in standard telecommunication wavelengths, in addition to providing the surrounding Si circuitry with noise immunity from signaling. The transconductance of the FET provides amplification, and an experimental current gain of up to 1000 is demonstrated. A complementary function is shown by tailoring the doping profiles. The circuit performance of a complementary pair using the International Technology Roadmap for Semiconductors values for the 150-nm node is evaluated by simulation, yielding ~100-ps cycle times. The switch can be fabricated in the nanoscale regime along with a high-performance Si complementary MOS. A very low capacitance can be achieved due to the isolation of the detection region from the current drive. OE conversion that is performed with such a compact device offers the potential of inserting light at the latch level in a microprocessor. [ABSTRACT FROM AUTHOR]

We show that the conventional nonparabolic approximation of real band structures can be modified and generalized to approximate the complex band structures of common semiconductors with a significant improvement of accuracy against the parabolic approximation. The improvement is due to the inherent elliptic nature of the complex band structures in the vicinity of the bandgap, which has a critical impact on the band-to-band tunneling probability. Important parameters are extracted and tabulated for Si, Ge, GaAs, and GaSb, with a maximum error of < 1.4% compared to the numerical target. [ABSTRACT FROM PUBLISHER]

In this work, we use thin dielectrics to reduce the Al/n-GaAs effective barrier height ([uppercase_phi_synonym]B,eff) of metal-insulator-semiconductor (MIS) contacts. We investigate the use of atomic layer deposition of HfO2, Al2O3, TiO2, ZrO2, and bilayer high-κ dielectrics and confirm there is a shift in the Fermi level that reduces the contact resistance. In studying high-κ/high-κ interfaces, we find that despite a thicker dielectric, there is further reduction in [uppercase_phi_synonym]B,eff beyond that of a single dielectric, which can be explained by the formation of a high-κ/high-κ dipole. This MIS structure provides great flexibility in the design of source/drain contacts for III-V transistors. [ABSTRACT FROM AUTHOR]

The characteristics of surface states on Ge are investigated using metal/insulator/semiconductor structures and the conductance technique. Evidence of acceptor-like and donor-like surface states on the valence band side of the Ge bandgap is shown by trap time constant analysis. The dependency of trap time constants on trap energy separation from band edge, capture cross section, and temperature are studied through conductance measurements and simulations. The effect of surface states on the location of charge neutrality level at the Ge surface and the consequences such as surface conductivity and negative charge buildup at the interface are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate high performance Ge N+/P and P+/N junction diodes at sub-380 °C. Very low resistivity (2.2×10-4 Ω cm) and shallow (92 nm) junction with high degree of dopant activation are achieved especially in N+/P junction formed at 360 °C on Ge epitaxially grown on Si using complementary metal-oxide semiconductor process compatible-metal (Co) induced dopant activation technique. Excellent diode characteristics having ∼2×104 on/off ratio and high forward current density (221 A/cm2 for N+/P and 135 A/cm2 for P+/N at |VF|=2 V) are obtained in N+/P and P+/N junction diodes fabricated at 380 °C on bulk Ge with a surface passivated layer [GeO2+low temperature chemical vopor deposition SiO2 (LTO)] isolation. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate and characterize a vertical (current flow that is perpendicular to the wafer) source (bottom)/drain (top) double-gate capacitorless single-transistor DRAM on a bulk silicon wafer. We have electrically measured retention times in excess of 25 ms. Device fabrication was facilitated by several key process innovations, which allow the device to also be integrated with planar devices using minimal additional process steps. The structure results in a highly scalable DRAM down to 22-nm technology node. [ABSTRACT FROM AUTHOR]

A few of the recent unsatisfactory germanium n-channel metal-oxide-semiconductor field-effect transistor MOSFET experimentations are believed to stem from the poor source and drain n+-p junction formations. In order to explain the primary cause and suggest rectifying solutions, we have examined the activation of common n-type dopants in germanium and the related dependences. These dependences include thermal anneal budget, impurity species, and implantation dosage. Low thermal budgets are generally preferred to activate shallow junctions to simultaneously annihilate defects and suppress fast dopant diffusion. Injecting dopants over the solid-solubility limitation into shallow junctions would only generate more implantation damage but could not however lower the junction sheet resistance. [ABSTRACT FROM AUTHOR]

The microstructural and electrical properties of Ge-based metal–oxide–semiconductor capacitors containing high-k gate dielectric layers were investigated with and without the presence of a GeOxNy interface layer. The effect of this nitrided layer on thermal stability of the metal oxide/Ge structures was probed by medium energy ion energy spectroscopy (MEIS). Atomic-layer deposited HfO2 on a chemical oxide-terminated Ge (100) surface exhibited poor capacitance–voltage behavior; however, direct substrate surface nitridation at 600 °C in NH3 ambient before HfO2 deposition improved the carrier trapping characteristics. Diffusion of metal impurities (including Hf) into the interfacial oxide/Ge-substrate may be an important source of the measured degradation of electrical properties. MEIS results suggested that the GeOxNy interface layer may inhibit Hf diffusion into the underlying semiconductor at the temperatures investigated. [ABSTRACT FROM AUTHOR]

We have studied the effect of varying electrode area asymmetry on the leakage behavior of metal-semiconductor-metal photodetectors (MSM-PDs). We demonstrate, an effective suppression of dark current (Idark) with the application of asymmetric electrode area and appropriate biasing scheme in MSM-PDs. More than 2× reduction in Idark is obtained in photodetectors fabricated on silicon. Photoresponse of these detectors have also been monitored and normalized photo-to-dark current ratio (NPDR) metric is utilized for objective assessment of detector performance. Significant enhancement in NPDR is shown to be accomplished with the asymmetric Si MSM-PDs. [ABSTRACT FROM AUTHOR]

Semiconductorheterostructures play a vital role in photonics andelectronics. They are typically realized by growing layers of differentmaterials, complicating fabrication and limiting the number of uniqueheterojunctions on a wafer. In this Letter, we present single-materialnanowires which behave exactly like traditional heterostructures.These pseudoheterostructures have electronic band profiles thatare custom-designed at the nanoscale by strain engineering. Sincethe band profile depends only on the nanowire geometry with this approach,arbitrary band profiles can be individually tailored at the nanoscaleusing existing nanolithography. We report the first experimental observationsof spatially confined, greatly enhanced (>200×), and wavelength-shifted(>500 nm) emission from strain-induced potential wells that facilitateeffective carrier collection at room temperature. This work representsa fundamentally new paradigm for creating nanoscale devices with fullheterostructure behavior in photonics and electronics. [ABSTRACT FROM AUTHOR]

Abstract: In X Ga1− X Sb has the highest hole mobility amongst all III–V semiconductors which can be enhanced further with the use of strain. The use of confinement and strain in In X Ga1− X Sb quantum wells lifts the degeneracy between the light and heavy hole bands which leads to reduction in the hole effective mass in the lowest occupied band and an increase in the mobility. We present magnetotransport measurements on compressively strained In X Ga1− X Sb and GaSb quantum wells. Hall-bar and Van de Pauw structures were fabricated and Shubnikov–de Haas oscillations in the temperature range of T =2–10K for magnetic fields of B =0–9T were measured. The reduction of effective hole mass with strain was quantified. These results are in excellent agreement with modeling results from band structure calculations of the effective hole mass in the presence of strain and confinement. [Copyright &y& Elsevier]