Although two-dimensional monolayer transition-metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS2 via ambient gases. The work function was measured by an in situ Kelvin probe technique and further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O2 exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ∼200 nm, which is much...

Large Work Function Modulation of Monolayer MoS2 by Ambient Gases

The origin of p–n junction reverse current is investigated by a method based on the analysis of the leakage current activation energy. Its main advantages lie in the possibility to distinguish multiple reverse-bias dependent leakage components and determine their mechanisms, which can be different than the Shockley–Read–Hall or field-enhanced generation mechanisms. This is illustrated for state-of-the-art silicided shallow junctions, exhibiting a local Schottky effect, due to small-area silicide penetrations. An estimate of the area of the Schottky (or Shannon) contacts follows from the analysis. The method may be used for various semiconductor materials and leakage current origins.

Activation energy analysis as a tool for extraction and investigation of p–n junction leakage current components

Review—Carrier Lifetime Spectroscopy for Defect Characterization in Semiconductor Materials and Devices

This overview focuses on the different types of noise occurring in deep submicrometer silicon metal oxide semiconductor field-effect transistors and their use as an analytical tool. The noise sources comprise white noise, generation-recombination noise, random telegraph signal fluctuations, and 1/f or flicker noise. The fundamental basis of each noise type is briefly described and illustrated by some practical examples. In a second part, the impact of the properties of the silicon substrate (orientation, crystallization technique, silicon-on-insulator, SiGe) on the noise performance is discussed. Finally, the influence on the low-frequency noise behavior of different advanced process modules, such as gate stack, device isolation, silicidation, and gate engineering, is illustrated.

Low-Frequency Noise Assessment for Deep Submicrometer CMOS Technology Nodes

The application of high-voltage reverse current to voltage characteristics for characterization of ultra-deep radiation defect profiles in ion irradiated silicon p-i-n diodes is presented. Theoretical analysis shows that monitoring of the reverse current gradient with increasing bias can give, in combination with Deep Level Transient Spectroscopy (DLTS) and Capacitance–Voltage (C–V) measurement, quantitative information about the distribution of generation defect centres with the highest emissivity. The method is subsequently used for characterization of deep-level profiles in p + pnn + power diodes irradiated by He 2+ ions with energies 11–22 MeV and fluences 2.5 × 10 9 –1.2 × 10 10 cm −2 . The results show that the method can non-destructively determine the concentration profile of divacancies, the dominant generation centre in helium irradiated silicon, in the depths of the device where application of other methods usually fails.

Divacancy profiles in MeV helium irradiated silicon from reverse I–V measurement

In this paper, the reverse current characteristics of Si p-n junction diodes are analyzed in detail, in order to obtain an improved analysis of the underlying material parameters (generation and recombination lifetime, thermal activation energy). For that purpose, measurements on different geometry diodes are combined in order to separate peripheral from volume components. Using the correct depletion capacitance of the p-n junction, one can separate the diffusion from the generation component. From a study of the behavior with changing temperature, it is concluded that the peripheral generation component is due to surface generation by interface states. This is further supported by measurements on gated diodes, which yield an extra feature that is speculated to be related to the surface generation along the isolation oxide edges. For the volume generation component, widely different activation energies have been found, depending on whether an internal gettering step was applied or not. A good agreement with deep-level parameters and trap profiles obtained by deep level transient spectroscopy has been found. In the case of Czochralski material, there exists a clear correlation with the oxygen-precipitation related extended defects. Finally, it is reported that the electric field dependence of the generation current component is stronger than expected from the Poole-Frenkel effect only, with an activation energy lowering which is much greater. Trap-assisted tunneling is a possible explanation.

Optimized Diode Analysis of Electrical Silicon Substrate Properties

An accurate method for the extraction of the reverse diffusion current component in a silicon p-n junction diode is proposed. It combines capacitance–voltage and current–voltage measurements on an array of diodes with different geometry in order to separate the peripheral and the volume leakage current components. The corrected volume capacitance is then used to calculate the depletion width as a function of the reverse bias. Extrapolation of the reverse current to zero depletion width results in the diffusion current part, both for the volume and for the peripheral component. From the temperature dependence, a thermal activation energy of 1.12 eV is obtained. The volume diffusion current density of the p-type Czochralski wafers studied, shows a pronounced substrate dependence, while the peripheral diffusion current density is constant. Finally, the implications for the extraction of the effective bulk recombination lifetime are discussed.

Accurate extraction of the diffusion current in silicon p-n junction diodes

An improved analysis of the p‐n junction current‐voltage (I‐V) and capacitance‐voltage (C‐V) characteristics is proposed and applied to diodes fabricated in a variety of silicon substrates. It is shown that for state‐of‐the‐art processing conditions the diffusion current at room temperature dominates the volume leakage current. The peripheral component, on the other hand, is governed by the surface generation in the bird's‐beak region surrounding the complementary metal oxide semiconductor compatible diodes. Nevertheless, a small substrate effect is observed, which can only be resolved by the proposed optimized analysis. For epitaxial wafers, the presence of the highly doped substrate can significantly reduce the volume diffusion current, while for internally gettered Czochralski material the presence of a highly defective bulk region under the denuded zone enhances this current. This complicates the recombination lifetime extraction from I‐V characteristics. © 1999 The Electrochemical Society. All rights reserved.

p‐n Junction Diagnostics to Determine Surface and Bulk Generation/Recombination Properties of Silicon Substrates

Statistical analysis of shallow p-n junction leakage increase using XTEM results probabilities

The p–n junction leakage ( I R ) at reverse voltage, which sets the leakage and power consumption of state of the art integrated circuits (ICs) and the DRAM retention time, is mostly related to the peripheral leakage ( I R,p ), which is poorly controlled by the defect engineering techniques, opposite to the planar regions. These ICs from their processing till applications cope with irradiation damages, which are side effects of the ICs manufacturing, due to the plasma, e-beam, X-ray and implantation processing, etc. On the other hand, ICs may be submitted to a significant natural radiation level, as e.g. in applications for space satellites and airplane equipment. Therefore, a proper analysis of the I R,p degradation by high-energy irradiation in silicon technology is proposed. It is found that I R,p increases slower for low fluences of neutron irradiation as compared to the leakage of the p–n junction planar regions, so that the I R,p contribution to the total I R decreases. However I R,p still dominates in irradiated small-size junctions. Moreover, for higher fluences the I R,p again strongly increases its contribution to the overall leakage. Deep insight into the underlying physics is obtained by an analysis of the gated diodes current. This method saves test-chip area and testing-time and omits the assumption of the same parasitic leakage for all junctions. Results are reported for n + p gated diodes and p–n junctions in Czochralski, epitaxial and float zone silicon, exposed to 1 MeV fast neutrons with fluences in the range 5×10 11 –5×10 13 n / cm 2 .

J Katcki

Papers

Optimized Diode Analysis of Electrical Silicon Substrate Properties

Accurate extraction of the diffusion current in silicon p-n junction diodes

p‐n Junction Diagnostics to Determine Surface and Bulk Generation/Recombination Properties of Silicon Substrates

Statistical analysis of shallow p-n junction leakage increase using XTEM results probabilities

Impact of fast-neutron irradiation on the silicon p–n junction leakage and role of the diffusion reverse current