Germanium Devices Research Articles

Ultrafast hole spin qubit with gate-tunable spin-orbit switch functionality.

Quantum computers promise to execute complex tasks exponentially faster than any possible classical computer, and thus spur breakthroughs in quantum chemistry, material science and machine learning. However, quantum computers require fast and selective control of large numbers of individual qubits while maintaining coherence. Qubits based on hole spins in one-dimensional germanium/silicon nanostructures are predicted to experience an exceptionally strong yet electrically tunable spin-orbit interaction, which allows us to optimize qubit performance by switching between distinct modes of ultrafast manipulation, long coherence and individual addressability. Here we used millivolt gate voltage changes to tune the Rabi frequency of a hole spin qubit in a germanium/silicon nanowire from 31 to 219 MHz, its driven coherence time between 7 and 59 ns, and its Landé g-factor from 0.83 to 1.27. We thus demonstrated spin-orbit switch functionality, with on/off ratios of roughly seven, which could be further increased through improved gate design. Finally, we used this control to optimize our qubit further and approach the strong driving regime, with spin-flipping times as short as ~1 ns.

Impact of Gate Stack Layer Composition on Dynamic Threshold Voltage and Analog Parameters of Ge pMOSFETs

One of the main challenging issues for germanium (Ge) devices is the gate stack engineering which determines the interface state density (NIT) and the associated channel/oxide interface quality. This paper shows how this issue can play a role in p-channel Ge MOSFETs considering both the operation mode, i.e., comparing conventional, dynamic threshold voltage (DT, where VBS = VGS) and enhanced dynamic threshold voltage (eDT, where VBS=k*VGS) modes, and the main analog parameters like the Early voltage (VEA) and intrinsic voltage gain (AV). Moreover, the impact of different HfO2/Al2O3 gate stack thicknesses is under evaluation. Although the thinnest Al2O3 layer degrades all evaluated parameters, specifically: lower VEA and AV, higher drain current hysteresis and subthreshold swing (SS) due to the higher NIT, the dynamic threshold voltage showed to be an effective mode to strongly minimize the hysteresis effects and improves up to 60% in eDT (k = 2) mode compared to the conventional mode (k = 0), thanks to the dynamic threshold voltage reduction.

Ge Devices: A Potential Candidate for Sub-5-nm Nodes?

In this article, we explore different device and standard cell architectures for scaling the Germanium fin field-effect transistor (FinFET) and nanosheet (NS) at the sub-5-nm node. It is demonstrated that the Germanium device provides approximately 70% improvement in drive current and 3.4× less device resistance. The main concern for Germanium devices remains the high leakage current due to the gate-induced drain leakage, which limits their usage to high-speed applications. Overall, Germanium devices require fewer boosters than silicon to scale beyond the 5-nm node. Contact resistivity is found to be a critical knob for Germanium and it can be relaxed to 3e-9 Ω-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to meet the power and performance targets for the sub-5-nm node. Moving to the NS helps in relaxing this constraint further.

Improved performance of Al/n&lt;sup&gt;+&lt;/sup&gt;Ge Ohmic contact andGe n&lt;sup&gt;+&lt;/sup&gt;/p diode by two-step annealing method

Silicon based germanium devices are crucial parts of optoelectronic integration as CMOS feature size continuously decreases. Germanium has attracted increasing attention due to its higher electron and hole mobility, larger optical absorption coefficient as well as lower processing temperature than those of silicon. However, the high diffusion coefficient and low solid solubility about n-type dopant and relatively high thermal budget required for high n-type doping in Ge make it difficult to achieve high activation n-type doping and excellent n&lt;sup&gt;+&lt;/sup&gt;/p shallow junction for source/drain in the nano-scaled n-MOSFET (here MOSFET stands for). The high activation concentration and shallow junction n-type doping in Ge are greatly beneficial to the scaled Ge n-MOSFET technology. In this work, the ohmic contact of Al/n&lt;sup&gt;+&lt;/sup&gt;Ge and Ge n&lt;sup&gt;+&lt;/sup&gt;/p junction fabricated by a combination of low temperature pre-annealing process and excimer laser annealing for phosphorus-implanted germanium are demonstrated. Prior to excimer laser annealing, the samplesare annealed at a relatively low temperature, which can heal the implantation damages preliminarily. Through the optimization of pre-annealing temperature and time, the low temperature pre-annealing step can play a critical role in annihilating the implantation damages and significantly suppressing phosphorus diffusion in the laser annealing process, resulting in a very small dopant diffusion length at a high activation level of phosphorus. Through the combination of ion implantation and two-step annealing technology, the specific contact resistivity (&lt;i&gt;ρ&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;) of Al/n&lt;sup&gt;+&lt;/sup&gt;Ge Ohmic contact is measured by CTLM structure. The optimized annealing condition is 400 &lt;sup&gt;o&lt;/sup&gt;C-10 min of low temperature annealing and 150 mJ/cm&lt;sup&gt;2&lt;/sup&gt; of ELA. Under that annealing condition, the ρ&lt;sub&gt;C&lt;/sub&gt; of the sample by two-step annealing is reduced to 2.61 × 10&lt;sup&gt;–6&lt;/sup&gt; Ω·cm&lt;sup&gt;2&lt;/sup&gt;, which is one order of magnitude lower than that by ELA alone (about 3.44 × 10&lt;sup&gt;–4&lt;/sup&gt; Ω·cm&lt;sup&gt;2&lt;/sup&gt;). The lower value of &lt;i&gt;ρ&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt; for the sample with LTPA can contribute to the higher carrier concentration and better crystalline quality thanthat without LTPA, which is confirmed by SRP and TEM. Moreover, the rectification ratio of Ge n&lt;sup&gt;+&lt;/sup&gt;/p junction diode is improved to 8.35 × 10&lt;sup&gt;6&lt;/sup&gt; at ± 1 V, which is two orders of magnitudes higher than that by ELA alone. And a lower ideality factor of about 1.07 is also obtained than that by ELA alone, which indicates that the implantation damages can be repaired perfectly by two-step annealing method.

Model Development of p-i-n Germanium Devices for Infrared Detection

Germanium offers many benefits over groups III-V materials when used for infrared detection. Most importantly, germanium is compatible with Complementary Metal Oxide Semiconductor (CMOS) manufacturing which allows for a low-cost, high-throughput device, and it does not require cooling, which many III-V devices do. With the deposition of germanium directly on silicon, there will be a thermally induced strain due to the difference in thermal expansion coefficients between the two materials. When a biaxial tensile strain is present, the direct bandgap of germanium is lowered to ~0.77 eV and is capable of absorbing longer wavelengths. We have used a two-step deposition process to create a strained germanium film in order to fabricate a photodetector device. Our device has a dark current of 1.35 nA and a photocurrent of 22.5 nA at 1570 nm wavelength. Next, we developed a model in order to compare theoretical results with experimental results. The results indicate that the model is in close agreement with our measured data, and we are therefore able to use it to model future devices.

Designing a high performance, stable spectroscopic biosensor for the binding of large and small molecules

In the context of FTIR ATR-based sensors, the organic layer covering the ATR element has to be as stable as possible for optimal spectroscopic measurements. Previously, this self-assembled covering was considered stable after several hours under a PBS flux, probably due to a hydrophobic barrier, which prevents water penetration into the grafted network. Stability and reactivity, measured simultaneously using FTIR ATR, identify the limits of the previously used molecular construction. For the first time, surface etching of the previous functionalised Ge devices (Ge-PEG-NHS), a few minutes after BSA injection, was observed. It was concluded that the molecular chain deformation of Ge-PEG-NHS likely occurred when large molecules were bound. BSA loaded onto a Ge-PEG-NHS surface led to network deprotection, with the probable disruption of hydrogen bonds for single barrier-based networks. This, in turn, was presumably influenced by the random deposition of the NHS moiety on the PEG chain. A new functionalised germanium device, using a rapid three-step in situ procedure, provides an efficient robust network composed of two protective barriers, ideal for the binding of various sized molecules. The Ge-APS-PEG-NHS device has shown exceptional sensitivity with regards to BSA and ethanolamine target molecules while offering homogeneous NHS distribution.

Reliability of Post Plasma Oxidation Processed ALD Al2O3/Hf1-xZrxO2 Thin Films on Ge Substrates

Germanium devices are widely investigated due to their high hole and electron mobility compared to that of silicon. Mobility above 300 cm2V-1s-1 has been reported for Ge PMOS. On the other hand, Ge NMOS showed poor drive current and low mobility in previous studies. This poor performance is attributed to the inability to form a good Ge/high-k interface (1). They also exhibit hysteresis during the capacitance voltage (C-V) sweep because of the presence of slow trap states near the dielectric substrate interface (2). Recently, the use of a slot-plane-antenna (SPA) Ar plasma during the deposition of ALD Hf1-xZrxO2 on Si substrate was reported to enhance the EOT (equivalent oxide thickness) downscaling potential with a suppressed trap formation in the bulk oxide under electrical stress (3). In this work, we have investigated TiN/HfZrO/Al2O3/Ge gate stack using MOS capacitors with six different Zr/(Hf+Zr) content (0%, 25%, 33%, 50%, 75%, and 100%) in the dielectrics. The dielectrics were subjected to SPA plasma oxidation after the deposition process. Electrical characterization of these devices was studied in order to observe the impact of Zr addition in HfO2. The equivalent oxide thickness (EOT), flat-band voltage (VFB), interface state density (Dit), C-V hysteresis, and leakage current (I-V) behavior were analyzed. Figure 1 shows the comparison of EOT and VFB as a function of Zr content in the dielectrics. Figure 2 presents the C-V hysteresis data (to the left axis) and mid gap Dit (to the right axis) for these devices. The addition of Zr in HfO2 was found to enhance the EOT up to 75% Zr incorporation. These devices also showed lower hysteresis in the C-V characteristics. However, A reduction in EOT for these devices showed to increase the flat-band voltage shift (Fig. 1). While devices with 100% Zr showed the highest EOT value coupled with the lowest mid gap Dit, a reduction in EOT with Zr addition in HfO2 moderately increases the Dit (Fig. 2 to the right scale). Figure Captions: Fig. 1: Equivalent oxide thickness (filled squares to the right scale) and flat-band voltage (open triangles to the left scale) comparison for the addition of Zr in HfO2. Fig. 2: Hysteresis behavior extracted from C-V sweep first from accumulation to inversion and then from inversion to accumulation (filled squares to the left scale) and interface state density by conductance method (open circles to the right scale) for ALD Hf1-xZrxO2/Al2O3 gate stacks on Ge substrate.

Investigation of mid-infrared second harmonic generation in strained germanium waveguides.

In this paper we present a detailed theoretical investigation of second harmonic generation in strained germanium waveguides operating at the mid infrared pump wavelength of 4 μm. The effective second order susceptibility has been estimated through a multiphysics approach considering the residual stress of the SiNx cladding film. Furthermore, general physical features have been investigated by means of a comparative analysis of SHG performance as a function of input pump power, linear and nonlinear phase mismatching, effective recombination carrier lifetime, and temperature, taking into account both continuous and pulsed regimes. Finally, periodically poled germanium devices have been explored with the aim to improve the SHG efficiency. In the same operative conditions, efficiencies of 0.6% and 0.0018% have been obtained in poled and not-poled waveguides, respectively.

Viability of pattern shift for defect-free extreme ultraviolet lithography photomasks

Several challenges hinder extreme ultraviolet lithography (EUVL) photomask fabrication and its readiness for high-volume manufacturing (HVM). The lack in availability of pristine defect-free blanks as well as the absence of a robust mask repair technique mandates defect mitigation through pattern shift for the production of defect-free photomasks. By using known defect locations on a blank, the mask design can be intentionally shifted to avoid patterning directly over a defect. The work presented here provides a comprehensive look at pattern shift implementation to intersect EUV HVM for the 7-nm technology node (N7). An empirical error budget to compensate for various measurement errors, based on the latest HVM inspection and write tool capabilities, is first established and then verified postpatterning. The validated error budget is applied to 20 representative EUV blanks and pattern shift is performed using fully functional N7 chip designs that were recently used to fabricate working silicon–germanium devices. Probability of defect-free masks are explored for various N7 photomask levels, including metal, contact, and gate cut layers. From these results, an assessment is made on the current viability of defect-free EUV masks and what is required to construct a complete defect-free EUV mask set.

Millisecond non-melt laser annealing of phosphorus implanted germanium: Influence of nitrogen co-doping

In this work, we present the results obtained using a CO2 laser source at 10.6 μm wavelength for the study of the non-melt annealing of phosphorus doped germanium in the millisecond regime. Main objective of this paper is the demonstration of electrically active n+-p junctions in germanium by implanting phosphorus in p-type substrate while trying to maintain minimal dopant diffusion, which is a critical issue for scaling germanium devices. In addition to the phosphorus diffusion studies, we also explore the presence of nitrogen introduced in the substrate together with phosphorus and we conclude that it can further reduce dopant movement at the expense of lower activation level. The observation is confirmed by both electrical and SIMS measurements. Moreover, density functional theory calculations show that nitrogen-phosphorus co-doping of germanium creates stable N-P complexes that, indeed, are consistent with the deactivation and diffusion suppression of phosphorus.

Enhanced low field magnetoresistance in germanium and silicon-diode combined device at room temperature

We report on a large (∼200%), room-temperature, small field (20 mT) magnetoresistance effect in germanium and silicon-diode combined device. This enhanced magnetoresistance is attributed to geometry of germanium and nonlinear electro-transport characteristic of silicon-diode. A two-dimensional finite element model is built to simulate the experimental results. Our work may pave a way to develop low field magnetoresistance devices from germanium and silicon.

Electronic materials with a wide band gap: recent developments.

The development of semiconductor electronics is reviewed briefly, beginning with the development of germanium devices (band gap E g = 0.66 eV) after World War II. A tendency towards alternative materials with wider band gaps quickly became apparent, starting with silicon (E g = 1.12 eV). This improved the signal-to-noise ratio for classical electronic applications. Both semiconductors have a tetrahedral coordination, and by isoelectronic alternative replacement of Ge or Si with carbon or various anions and cations, other semiconductors with wider E g were obtained. These are transparent to visible light and belong to the group of wide band gap semiconductors. Nowadays, some nitrides, especially GaN and AlN, are the most important materials for optical emission in the ultraviolet and blue regions. Oxide crystals, such as ZnO and β-Ga2O3, offer similarly good electronic properties but still suffer from significant difficulties in obtaining stable and technologically adequate p-type conductivity.

Anisotropy-Driven Spin Relaxation in Germanium

A unique spin depolarization mechanism, induced by the presence of g-factor anisotropy and intervalley scattering, is revealed by spin-transport measurements on long-distance germanium devices in a magnetic field longitudinal to the initial spin orientation. The confluence of electron-phonon scattering (leading to Elliott-Yafet spin flips) and this previously unobserved physics enables the extraction of spin lifetime solely from spin-valve measurements, without spin precession, and in a regime of substantial electric-field-generated carrier heating. We find spin lifetimes in Ge up to several hundreds of nanoseconds at low temperature, far beyond any other available experimental results.

NiGe Contacts and Junction Architectures for P and As Doped Germanium Devices

In this paper, the contact resistivity of NiGe on n-doped Ge is extracted. Although phosphorus is the slowest n-type dopant in terms of diffusion in Ge, the corresponding contact resistivity data for this dopant are sparse. Contact resistivity dependence on implant dose will be determined, as well as a comparison of phosphorus- and arsenic-doped Ge layers. The impact of high contact resistance is evaluated for future technology n-type metal-oxide-semiconductor germanium devices.

Understanding the Potential and the Limits of Germanium pMOSFETs for VLSI Circuits From Experimental Measurements

In this paper, potential and limits of Germanium pMOSFETs for VLSI applications are investigated from a circuit perspective for the first time in the literature. Since short-channel Germanium devices have been developed only recently, no circuit design tools are currently available, hence most of the results available in the literature address process and device-level issues (currently, down to the 65 nm node). However, the suitability of Germanium MOSFETs for VLSI circuits should be assessed at circuit level. To fill this gap, we introduce an innovative methodology that extracts the main circuit parameters of interest (e.g., speed, dynamic power, leakage) from measurements on experimental devices. Appropriate figures of merit are adopted to highlight the potential of Germanium MOSFETs under realistic VLSI designs that fully exploit system-level schemes to minimize leakage (e.g., body biasing, stack forcing, power gating). Measurements and evaluations are performed on 125 nm Germanium pMOSFETs with a high-κ/metal gate stack having an equivalent oxide thickness of 1.3 nm. Comparison with Si pMOSFET prototypes implemented with similar gate stack is also carried out to comparatively understand the potential and the weaknesses of Germanium transistors. The main experimental results are justified through theoretical analysis as a function of the relevant circuit and device parameters. Some system-level aspects are also investigated, such as the energy efficiency and the wakeup time of body-biasing schemes in Ge circuits and the impact of voltage scaling.

A Complete Fabrication Route for Atomic-Scale, Donor-Based Devices in Single-Crystal Germanium

Despite the rapidly growing interest in Ge for ultrascaled classical transistors and innovative quantum devices, the field of Ge nanoelectronics is still in its infancy. One major hurdle has been electron confinement since fast dopant diffusion occurs when traditional Si CMOS fabrication processes are applied to Ge. We demonstrate a complete fabrication route for atomic-scale, donor-based devices in single-crystal Ge using a combination of scanning tunneling microscope lithography and high-quality crystal growth. The cornerstone of this fabrication process is an innovative lithographic procedure based on direct laser patterning of the semiconductor surface, allowing the gap between atomic-scale STM-patterned structures and the outside world to be bridged. Using this fabrication process, we show electron confinement in a 5 nm wide phosphorus-doped nanowire in single-crystal Ge. At cryogenic temperatures, Ohmic behavior is observed and a low planar resistivity of 8.3 kΩ/□ is measured.

Investigation on Morphology and Thermal Stability of NiGe Utilizing Ammonium Fluoride Pretreatment for Germanium-Based Technology

In this letter, a novel ammonium fluoride pretreatment (AFP) method has been proposed to improve the morphology and thermal stability of NiGe on bulk germanium devices. The root mean square roughness of NiGe film has been obviously decreased using the AFP method, indicating more smooth and flat NiGe surfaces formed compared with samples by hydrochloric acid and hydrofluoric acid pretreatments. Also, the thermal stability of NiGe film has been enhanced, since uniform NiGe film can be formed at temperature as high as 600°C. In addition, NiGe/n-Ge Schottky diodes have been fabricated to illustrate the benefits of AFP method in Ge-based devices. Better rectifying performance has been achieved using the AFP method from the benefit of suppressing reverse current about one order of magnitude, compared with the hydrochloric acid treated sample. Thus, both the material properties and electrical characteristics of NiGe film have been effectively improved by the simple AFP technique, revealing its potential for Ge-based process technology.

Optimization of SiGe bandgap-based circuits for up to 300 °C operation

An investigation of the performance and reliability issues associated with operating silicon–germanium (SiGe) devices and circuits at temperatures up to 300°C is presented, along with a new bypass compensation technique for optimizing bandgap reference performance at these extreme temperatures. In addition to the device-level characterization of a SiGe BiCMOS platform, improved circuit design and a device-level collector–substrate leakage suppression technique are shown to improve the viability of SiGe bandgap reference (BGR) circuits on low-cost, bulk Si wafers for high temperature applications. A shunting technique using various transistors to further improve BGR performance above 200°C is presented, and optimized compensation designs predict new performance records for a bulk-silicon based technology across temperatures from −200°C to 300°C. Finally, a closely-related SiGe temperature sensor circuit is characterized for operating environments up to 300°C.

(Invited) Novel Electronic and Optoelectronic Devices in Germanium Integrated on Silicon

In this paper we will review recent results on heterogeneous integration of novel electronic and optoelectronic Ge grown heteroepitaxial on Si. In the past work Ge has shown much promise for high performance MOSFETs and optical detectors. In this work we will discuss several other novel devices: tunnel FET (TFET), capacitorless quantum well single transistor DRAM (1T-QW DRAM), optical modulators and light emitters for on- and off-chip optical interconnects.

Novel Electronic and Optoelectronic Devices in Germanium Integrated on Silicon

not Available.