Slow Trap Research Articles

Comparative study of oxidizing ambient infused with varying nitrogen flow rates for fabrication of ternary nitrided AlZrO based MOS capacitor

High dielectric constant nitrided aluminum zirconium oxide films were successfully fabricated on silicon substrate via an oxidation process infused with different nitrogen gas flow rates at 800°C. The presence of nitrogen piling up at the interface could control the thickness of interfacial layer formation. An increase in the nitrogen gas flow rate might be effective in controlling the overall thickness of the films, yet the nitrogen piling up at the interface impeded the diffusion of oxygen to the interface. Consequently, the interface quality was affected, leading to degradation in the interface-state density. In addition, the generation of oxygen vacancies in the films, as well as the presence of nitrogen at the interstitial sites, would create a lattice polarization, which decreased the k values. Corresponding effects were also discussed in corroboration with energy band gap, effective oxide charges, and slow trap density, as well as interface-state density calculated from capacitance and conductance methods.

Growth and Characterization of Ternary Hf x Ta y O z Films via Nitrogen-Infused Wet Oxidation.

Nitrogen-infused wet oxidation at different temperatures (400–1000 °C) was employed to transform tantalum–hafnia to hafnium-doped tantalum oxide films. High-temperature wet oxidation at 1000 °C marked an onset of crystallization occurring in the film, accompanied with the formation of an interfacial oxide due to a reaction between the inward-diffusing hydroxide ions, which were dissociated from the water molecules during wet oxidation. The existence of nitrogen has assisted in controlling the interfacial oxide formation. However, high-temperature oxidation caused a tendency for the nitrogen to desorb and form N–H complex after reacting with the hydroxide ions. Besides, the presence of N–H complex implied a decrease in the passivation at the oxide–Si interface by hydrogen. As a consequence, defect formation would happen at the interface and influence the metal–oxide–semiconductor characteristics of the samples. In comparison, tantalum–hafnia subjected to nitrogen-infused wet oxidation at 600 °C has obtained the highest dielectric constant, the largest band gap, and the lowest slow trap density.

Lock-in Ultrafast Electron Microscopy Simultaneously Visualizes Carrier Recombination and Interface-Mediated Trapping.

Visualizing charge carrier flow over interfaces or near surfaces meets great challenges concerning resolution and vastly different time scales of bulk and surface dynamics. Ultrafast or four-dimensional scanning electron microscopy (USEM) using a laser pump electron probe scheme circumvents the optical diffraction limit, but disentangling surface-mediated trapping and ultrafast carrier dynamics in a single measurement scheme has not yet been demonstrated. Here, we present lock-in USEM, which simultaneously visualizes fast bulk recombination and slow trapping. As a proof of concept, we show that the surface termination on GaAs, i.e., Ga or As, profoundly influences ultrafast movies. We demonstrate the differences can be attributed to trapping-induced surface voltages of approximately 100–200 mV, which is further supported by secondary electron particle tracing calculations. The simultaneous visualization of both competing processes opens new perspectives for studying carrier transport in layered, nanostructured, and two-dimensional semiconductors, where carrier trapping constitutes a major bottleneck for device efficiency.

A systematic and quantitative analysis of the bulk and interfacial properties of the AlSiO dielectric on N-polar GaN using capacitance–voltage methods

The bulk and interfacial properties of aluminum silicon oxide (AlSiO) on N-polar GaN were investigated systematically employing capacitance–voltage (C–V) methods on metal–oxide–semiconductor capacitors using a thickness series of the AlSiO dielectric. The fixed charge density, electron slow trap density, and electron fast trap density located near the interface were extracted to be –1.5 × 1012 cm−2, 3.7 × 1011 cm−2, and 1.9 × 1011 cm−2, respectively. Using ultraviolet (UV) assisted C–V methods, an average interface state density of ∼4.4 × 1011 cm−2 eV−1 and a hole trap concentration in bulk AlSiO of ∼8.4 × 1018 cm−3 were measured. The negative fixed interface charge makes it favorable to achieve a normally off GaN transistor. The analysis presented in this paper provides a systematic and quantitative model to study the properties of oxide dielectrics on wide bandgap (WBG) semiconductors, which can promote the development of metal–oxide–semiconductor-based WBG semiconductor devices.

Reduction of MOS Interface Defects in TiN/Y₂O₃/Si₀.₇₈Ge₀.₂₂ Structures by Trimethylaluminum Treatment

We report improvement of TiN/Y2O3/ Si0.78Ge0.22 metal-oxide-semiconductor (MOS) interface properties by employing the trimethylaluminum (TMA) pretreatment before Y2O3 deposition. It is found that the optimum number of the TMA pretreatment cycles for minimizing interface trap density ( ${D}_{\text {it}}$ ) and slow trap density ( $\Delta {N}_{\text {st}}$ ) of TiN/Y2O3/SiGe interfaces with post metallization annealing (PMA) at 450 °C is ten cycles. The reduction in ${D} _{\text {it}}$ and $\Delta ~{N} _{\text {st}}$ is attributable to less amounts of Ge–O bonds at the SiGe interfaces. On the other hand, an increase in ${D} _{\text {it}}$ with further increasing the number of TMA pretreatment is attributable to more amounts of Al–O bonds in ILs.

Preparation and characterisation of aluminium zirconium oxide for metal‐oxide‐semiconductor capacitor

A functional type metal-oxide-semiconductor (MOS) based capacitor was fabricated and studied by using aluminium zirconium oxide (AlxZryOz) as a potential high dielectric constant (k) gate oxide, which was transformed from as-sputtered Al-Zr alloy after undergoing a wet oxidation at 400°C, 600°C, 800°C, and 1000°C in the presence of nitrogen as a carrier gas. A mixture of tetragonal ZrO2-monoclinic AlxZryOz phases were present at 600°C while stablized tetragonal AlxZryOz phases were detected at higher temperatures with a minute micro strain change. The largest k value (21) was obtained by the film oxidised at 600°C, followed by 800°C while the lowest one at 1000°C. The discrepancy was due to the absence of tetragonal ZrO2 in the latter films. The attainment of a k value closer to the reported value for ZrO2 at 600°C suggested that the tetragonal ZrO2 phase was one of the factors yielding a high k value at 600°C. However, further investigation was required for this sample because the slow trap density and total interface trap density was high despite a high k value, mainly attributed to the presence of negatively charged traps as the scattering centre in the film. The film obtained at 1000°C was not encourageable to be deployed as a passivation layer for Si MOS device due to its low k controlled by the thick interfacial layer.

Electron irradiation of multilayer PdSe2 field effect transistors

Palladium diselenide () is a recently isolated layered material that has attracted a lot of interest for its pentagonal structure, air stability and electrical properties that are largely tunable by the number of layers. In this work, multilayer is used as the channel of back-gate field-effect transistors, which are studied under repeated electron irradiations. Source-drain electrodes enable contacts with resistance below . The transistors exhibit a prevailing n-type conduction in high vacuum, which reversibly turns into ambipolar electric transport at atmospheric pressure. Irradiation by electrons suppresses the channel conductance and promptly transforms the device from n-type to p-type. An electron fluence as low as dramatically changes the transistor behavior, demonstrating a high sensitivity of to electron irradiation. The sensitivity is lost after a few exposures, with a saturation condition being reached for fluence higher than . The damage induced by high electron fluence is irreversible as the device persists in the radiation-modified state for several hours, if kept in vacuum and at room temperature. With the support of numerical simulation, we explain such a behavior by electron-induced Se atom vacancy formation and charge trapping in slow trap states at the interface.

Surface passivation via two-step grown nitrogen infused oxidation derived quaternary AlxZr1−xOyNz

High dielectric constant (k) quaternary AlxZr1-xOyNz was fabricated for silicon (Si)-based metal–oxidesemiconductor (MOS) devices via nitrogen infused oxidation at 600 °C. A higher k value (30.2) was attained due to accumulation of nitrogen at the oxide-Si interface to impede interfacial layer formation, yielding a reduced average oxide thickness. The presence of nitrogen was verified via detection of absorption spectra for Si-N and Si-N-Si. Interface quality of AlxZr1−xOyNz was investigated using Terman’s, high-low frequency, and conductance methods. The acquisition of low effective oxide charge and slow trap density further supported that AlxZr1−xOyNz possessed good passivation property for potential use in MOS devices.

SiC Strained nMOSFETs With Enhanced High- Frequency Performance and Impact on Flicker Noise and Random Telegraph Noise

Silicon–carbon (SiC) strained nMOSFETs with sub-35-nm gate length in a 40-nm CMOS technology can realize superior cutoff frequency ( $f_{T}$ ) up to 405 GHz, attributed to more than 20% enhancement of the mobility and transconductance. This super-400-GHz $f_{T}$ makes SiC strained nMOS an attractive high mobility device aimed at millimeter-wave (mm-wave) CMOS circuits design. However, the SiC nMOSFETs reveal a dramatic increase in flicker noise and random telegraph noise (RTN), which may cause worse phase noise and detrimental impact on CMOS oscillator stability. The complex RTN features abnormally long capture and emission time constants ( $\tau _{c}$ and $\tau _{e}$ ) and suggests electron-phonon coupling responsible for the anomalously slow trapping and detrapping, due to a significant increase of relaxation energy from SiC strain. This critical tradeoff between high-frequency performance and low-frequency noise becomes a key factor to be considered for the most appropriate adoption of high mobility devices and design optimization adapted to various circuits.

Trap analysis of composite 2D–3D channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C multi-heterostructure at different temperatures**Project supported by the National Key Research and Development Program of China (Grant No. 2018YFB1802100), the Natural Science Foundation of Shaanxi Province, China (Grant Nos. 2020JM-191 and 2018HJCG-20), the National Natural Science Foundation of China (Grant Nos. 61904135, 61704124, and 61534007), the China Postdoctoral Science Foundation (Grant Nos. 2018M640957

The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases (3DEGs) at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional (2D)–three-dimensional (3D) channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure (DH:Si/C). Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure (SH:C). There are fast, medium, and slow trap states in DH:Si/C, while only medium trap states exist in SH:C. The time constant/trap density for medium trap state in SH:C heterostructure are (11 μs–17.7 μs)/(1.1 × 1013 cm−2·eV−1–3.9× 1013 cm−2·eV−1) and (8.7 μs–14.1 μs)/(0.7× 1013 cm−2·eV−1–1.9× 1013 cm−2·eV−1) at 300 K and 500 K respectively. The time constant/trap density for fast, medium, and slow trap states in DH:Si/C heterostructure are (4.2 μs–7.7 μs)/(1.5× 1013 cm−2·eV−1–3.2× 1013 cm−2·eV−1), (6.8 μs–11.8 μs)/(0.8× 1013 cm−2 · eV−1–2.8× 1013 cm−2 · eV−1), (30.1 μs–151 μs)/(7.5× 1012 cm−2 · eV−1–7.8× 1012 cm−2 · eV−1) at 300 K and (3.5 μs–6.5 μs)/(0.9× 1013 cm−2 · eV−1–1.8× 1013 cm−2 · eV−1), (4.9 μs–9.4 μs)/(0.6× 1013 cm−2 · eV−1–1.7× 1013 cm−2 · eV−1), (20.6 μs–61.9 μs)/(3.2× 1012 cm−2 · eV−1–3.5× 1012 cm−2·eV−1) at 500 K, respectively. The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.

Significant reduction of interface trap density of SiC PMOSFETs by post-oxidation H2O annealing processes with different oxygen partial pressures

We investigated the effects of the post-oxidation annealing in H2O (wet-POA) with various conditions after dry oxidation for p-type 4H-SiC (0001) metal-oxide-semiconductor (MOS) capacitors and 4H-SiC (0001) p-channel MOS field-effect transistors (PMOSFETs). Interface state density, fixed charge density, and slow trap density in near-interface oxide were reduced by the wet-POA with additional growth of only <1 nm oxide at the interface. With those POAs the improved PMOSFET performance was also demonstrated. The degradation of flatband voltage (VFB) stability, which has been regarded as one of the serious drawbacks of wet oxidation of SiC, was efficiently suppressed by a careful selection of the wet-POA conditions with low O2 partial pressure at high temperature. Even though the reason why the VFB stability is so sensitive to the wet-POA condition is not clarified yet, these results give us a guideline to design wet-POA conditions appropriate for SiC PMOSFETs.

Impact of Electrical Stress on Defect Generation in Thin GeO2/Ge Gate Stacks Fabricated by Thermal Oxidation

The impact of electrical stress on the defect generation behaviors in thin GeO2/n-Ge gate stacks has been investigated through the measurement of the time-dependent dielectric breakdown (TDDB) and the stress-induced leakage current (SILC) characteristics. A multiple-spot breakdown (BD) event is confirmed, as well as a larger SILC generation probability compared with that in SiO2/Si structures. It is found that the slow trap generation is dominant by the amount of injected electron fluence ( ${Q} _{{\text {inj}}}$ ), and the fix charge generation is attributed to both ${Q} _{{\text {inj}}}$ and GeO2 thickness.

Atomic Layer Densification of AlN Passivation Layer on Epitaxial Ge for Enhancement of Reliability and Electrical Performance of High-K Gate Stacks

The impact of atomic layer bombardment (ALB) on the aluminum nitride (AlN) passivation layer between the HfO2 gate dielectric and the n-type epitaxial germanium (Ge) was investigated. The ALB technique was performed with the layer-by-layer, in situ helium/argon plasma bombardment in each cycle of atomic layer deposition (ALD) of AlN. An increase in the film density and a decrease in nitrogen vacancies, as manifested by the X-ray reflection and X-ray spectroscopy, were observed in the AlN layer treated by the ALB process. The improvements in the AlN quality contribute to a reduction of the equivalent oxide thickness from 1.36 to 1.19 nm of the AlN/HfO2 gate stack, together with the suppression of the gate leakage current, the interfacial state density, and the slow trap density. The reliability tests reveal promising reliability of the AlN/HfO2 gate stack with a small flat-band voltage shift under the constant voltage stress and a high operation voltage of ∼2.4 V projected for a 10 years time-dependent-dielectric-breakdown lifetime. All of the results point that the ALB technique can effectively enhance the material/interface properties, electrical characteristics, and reliability of nanoscale devices, which is critical and beneficial to the next-generation high-speed and low-power nanoelectronics.

Temperature-dependent study of slow traps generation mechanism in HfO2/GeON/Ge(1 1 0) metal oxide semiconductor devices

The lower mobility for p-type Ge based is always an issue due to slow traps generation at the interface of the metal oxide semiconductor (MOS) device which designates the defects in films generated during the deposition process. One of the effective ways to reduce this slow traps generation is to perform post deposition annealing (PDA) at a certain temperature. However, the selection of proper annealing temperature is the key to reduce defects without damaging the film quality. The effect of different PDA temperatures on the slow traps generation mechanism in the GeON passivated Ge MOS device was examined in this work. The XPS spectra show the stable formation of GeON over Ge, while HRTEM does not show any effect of PDA at the interface of GeON/Ge. The slow trap density (ΔNst) in HfO2/GeON/Ge interface annealed at different temperatures was evaluated from the hysteresis curve of C-V sweep as the function of the effective oxide field. The lowest ΔNst (4.01 × 1012 cm−2) was observed for the PDA temperature for 400 ℃. While, ΔNst increased slightly after PDA at 450 ℃. The work suggests that PDA at lower temperatures is essential to realize the high quality interface with lower interface trap density, enhanced mobility and lower CET in Ge based MOS devices. Further, it also helps to reduce the slow traps generations at the interface.

Chimp optimization algorithm

This paper proposes a novel metaheuristic algorithm called Chimp Optimization Algorithm (ChOA) inspired by the individual intelligence and sexual motivation of chimps in their group hunting, which is different from the other social predators. ChOA is designed to further alleviate the two problems of slow convergence speed and trapping in local optima in solving high-dimensional problems. In this paper, a mathematical model of diverse intelligence and sexual motivation of chimps is proposed. In this regard, four types of chimps entitled attacker, barrier, chaser, and driver are employed for simulating the diverse intelligence. Moreover, four main steps of hunting, i.e. driving, chasing, blocking, and attacking, are implemented. The proposed ChOA algorithm is evaluated in 3 main phases. First, a set of 30 mathematical benchmark functions is utilized to investigate various characteristics of ChOA. Secondly, ChOA was tested by 13 high-dimensional test problems. Finally, 10 real-world optimization problems were used to evaluate the performance of ChOA. The results are compared to several newly proposed meta-heuristic algorithms in terms of convergence speed, the probability of getting stuck in local minimums, and exploration, exploitation. Also, statistical tests were employed to investigate the significance of the results. The results indicate that the ChOA outperforms the other benchmark optimization algorithms.

Light-Induced Defect Healing and Strong Many-Body Interactions in Formamidinium Lead Bromide Perovskite Nanocrystals.

Organic lead halide perovskite (OLHP) nanocrystals (NCs) have paved the way to advanced optoelectronic devices through their extraordinary electrical and optical properties. However, understanding of the light-induced complex dynamic phenomena in OLHP NCs remains a subject of debate. Here we used wide field microscopy and time-resolved spectroscopy to correlate the local changes in photophysics and the dynamical behavior of photocarriers. We demonstrate that light-induced brightening of the photoluminescence from the formamidinium lead bromide NC films is related to the film preparation condition and reduction of trap density. The density of trap states is reduced via halide ion migration from interstitial position. Our femtosecond transient absorption study identifies transient Stark effect due to the generation of hot carriers. Because of slow carrier trapping, Auger recombination through many-body carrier-carrier interactions dominates over trion recombination. This work presents unprecedented insights into the light-driven processes enabling better device design in the future.

Multi-Cluster Jumping Particle Swarm Optimization for Fast Convergence

Particle Swarm Optimization (PSO) is a metaheuristic evolutionary computation technique inspired by the social behavior of birds and fish flock. The classical PSO has limitations of slow convergence rate and trapping in local minima, as the dimensions of the data increase. Moreover, majority of improvements made by the researchers in optimization techniques have focused on the accuracy of solution and have overlooked the convergence speed of an algorithm. Keeping in view the need of an optimization algorithm with fast convergence speed, suitable for high dimensional data space, this article proposes a novel concept of Multi-Cluster Jumping PSO. In the proposed method, the particles in the swarm are divided in different clusters to search for the global optimum solution. Each cluster in the swarm has its own cluster best position which is the best position within a cluster and the global best position is located by clusters communication. In order to avoid trapping in the local optima, a jumping strategy is incorporated for stuck particles through relocation of particles to a random new position. Instead of random initialization of the particles, a semi-random initialization is opted by dividing the entire search space and the distribution of particles over a search space is done in independent slots. The proposed approach has the ability to overcome the limitations of classical evolutionary computation methods and is suitable for high dimensional dynamic data. An extensive experimentation is carried out to optimize twelve benchmark functions using the proposed Multi-Cluster Jumping PSO and a significant difference is observed in the convergence speed of the proposed method over the existing state-of-the-art approaches.

A low-temperature supercritical nitridation technology for enhancing the performance of AlGaN/GaN HEMTs

A non-destructive low-temperature supercritical nitridation (LTSCN) is proved to boost the performance of AlGaN/GaN HEMTs. The samples were treated at 120 ℃ in a supercritical CO2 fluid mixed with NH3 under 20.7 MPa for one hour. After the LTSCN, the gate leakage current decreases by 69.6 % for an increase of the Schottky barrier height and the subthreshold swing is reduced by 19.9 %. Furthermore, the on-resistance is reduced by 20.4 % due to an enhancement of the mobility. The slow trap state density near AlGaN/GaN interface decreases from (5.12×1013 to 7.07×1013) cm−2·eV−1 to (1.80×1013 to 2.36×1013) cm−2·eV−1 with a decrease in activation energy from (0.492 to 0.500) eV to (0.467 to 0.496) eV after the LTSCN. A modified model of the LTSCN is presented to expound the change of the slow traps and the Coulomb scattering effect of electrons capture in the changed slow traps is adopted to explain the mobility improvement.

Reduction of Slow Trap Density in Al2O3/GeO x N y /n-Ge MOS Interfaces by PPN-PPO Process

The realization of high- ${k}$ /IL/Ge MOS interfaces with thin equivalent oxide thickness (EOT), low interface state density ( $\text{D}_{{\text {it}}}$ ), and high reliability is strongly needed for realizing Ge metal–oxide–semiconductor field-effect transistors (MOSFETs). In this article, we examine the properties of the slow trap areal density ( $\Delta \text{N}_{{\text {st}}}$ ) and $\text{D}_{{\text {it}}}$ in Al2O3/GeOxN y /n-Ge MOS interfaces formed by atomic layer deposition (ALD) Al2O3 films with plasma post nitridation (PPN) and plasma post oxidation (PPO). Here, the process order and process time of PPN and PPO are systematically changed to optimize the Al2O3/GeO x N y /n-Ge MOS interface properties. It is found that N atoms induced into GeO x can suppress slow electron trapping. An Al2O3/n-Ge structure with 1-min PPN before PPO can reduce $\Delta \text{N}_{{\text {st}}}$ by 34% in a weak electric field, whereas PPN after PPO increase $\Delta \text{N}_{{\text {st}}}$ . Also, the sufficient time PPO process after PPN can decrease $\text{D}_{{\text {it}}}$ to a similar level as that at the Al2O3/GeO x /n-Ge MOS interfaces. The temperature dependence of electron trapping properties is also experimentally evaluated. The slow electron trapping is expected to be more suppressed for the GeO x N y interfaces at real device operation temperature.

Can we see defects in capacitance measurements of thin‐film solar cells?

AbstractThermal admittance spectroscopy and capacitance‐voltage measurements are well established techniques to study recombination‐active deep defect levels and determine the shallow dopant concentration in photovoltaic absorbers. Applied to thin‐film solar cells or any device stack consisting of multiple layers, interpretation of these capacitance‐based techniques is ambiguous at best. We demonstrate how to assess electrical measurements of thin‐film devices and develop a range of criteria that allow to estimate whether deep defects could consistently explain a given capacitance measurement. We show that a broad parameter space, achieved by exploiting bias voltage, time, and illumination as additional experimental parameters in admittance spectroscopy, helps to distinguish between deep defects and capacitive contributions from transport barriers or additional layers in the device stack. On the example of Cu(In,Ga)Se2 thin‐film solar cells, we show that slow trap states are indeed present but cannot be resolved in typical admittance spectra. We explain the common N1 signature by the presence of a capacitive barrier layer and show that the shallow net dopant concentration is not distributed uniformly within the depth of the absorber.