Donor-like Defects Research Articles

Improving the Thermal Stability of Indium Oxide n-Type Field-Effect Transistors by Enhancing Crystallinity through Ultrahigh-Temperature Rapid Thermal Annealing.

Ultrathin indium oxide films show great potential as channel materials of complementary metal oxide semiconductor back-end-of-line transistors due to their high carrier mobility, smooth surface, and low leakage current. However, it has severe thermal stability problems (unstable and negative threshold voltage shifts at high temperatures). In this paper, we clarified how the improved crystallinity of indium oxide by using ultrahigh-temperature rapid thermal O2 annealing could reduce donor-like defects and suppress thermal-induced defects, drastically enhancing thermal stability. Not only does more crystalline indium oxide depict the high stability of threshold voltage in stringent high-temperature test environments and under positive bias, but it also shows much less degradation under forming gas annealing than as-deposited transistors. Furthermore, we also successfully solved the channel length-dependent threshold voltage problem, which is often observed in oxide transistors, by suppressing defects induced by the metal deposition process and metal doping.

Deconvolution of light- and heavy-hole contributions to measurements of the temperature-dependent Hall effect in zincblende copper iodide

This study presents a detailed experimental investigation of conductivity and Hall effect measurements in copper iodide (CuI), which is complemented by density-functional theory and Boltzmann-transport calculations. We have evaluated the temperature dependence of the transport data of solution-grown bulk single crystals, textured thin films grown by pulsed laser deposition, and additional data published in the literature. The density of compensating donorlike defects is determined from fits comprising ionized-impurity scattering. This is considered for determining acceptor densities and corresponding activation energies. In the course of this investigation, meticulous attention has been paid to the intricate interplay between light-hole and heavy-hole contributions, as well as the experimental values observed in zincblende CuI. This study has yielded two distinct ionization energies for acceptors in unintentionally doped CuI, with values of EI,1=95 meV and EI,2=330 meV, respectively. Published by the American Physical Society 2024

Additive-Assisted Hydrothermal Growth Enabling Defect Passivation and Void Remedy in Antimony Selenosulfide Solar Cells.

Antimony selenosulfide (Sb2(S,Se)3) has recently emerged as a promising light-absorbing material, attributed to its tunable photovoltaic properties, low toxicity, and robust environmental stability. However, despite these advantages, the current record efficiency for Sb2(S,Se)3 solar cells significantly lags behind their Shockley-Queisser limit, especially when compared to other well-established chalcogenide-based thin-film solar cells, such as CdTe and Cu(In,Ga)Se2. This underperformance primarily arises from the formation of unfavorable defects, predominately located at deep energy levels, which act as recombination centers, thereby limiting the potential for performance enhancement in Sb2(S,Se)3 solar cells. Specifically, deep-level defects, such as sulfur vacancy (VS), have a lower formation energy, leading to severe non-radiative recombination and compromising device performance. To address this challenge, thioacetamide (TA), a sulfur-containing additive is introduced, into the precursor solution for the hydrothermal deposition of Sb2(S,Se)3. This results indicate that the incorporation of TA helps in passivating deep-level defects such as sulfur vacancies and in suppressing the formation of large voids within the Sb2(S,Se)3 absorber. Consequently, Sb2(S,Se)3 solar cells, with reduced carrier recombination and improved film quality, achieved a power conversion efficiency of 9.04%, with notable improvements in open-circuit voltage and fill factor. This work provides deeper insights into the passivation of deep-level donor-like VS defects through the incorporation of a sulfur-containing additive, highlighting pathways to enhance the photovoltaic performance of Sb2(S,Se)3 solar cells.

Effects of Annealing Temperature on Bias Temperature Stress Stabilities of Bottom-Gate Coplanar In-Ga-Zn-O Thin-Film Transistors

Defect annihilation of the IGZO/SiO2 layer is of great importance to enhancing the bias stress stabilities of bottom-gate coplanar thin-film transistors (TFTs). The effects of annealing temperatures (Ta) on the structure of the IGZO/SiO2 layer and the stabilities of coplanar IGZO TFTs were investigated in this work. An atomic depth profile showed that the IGZO/SiO2 layer included an IGZO layer, an IGZO/SiO2 interfacial mixing layer, and a SiO2 layer. Higher Ta had only one effect on the IGZO layer and SiO2 layer (i.e., strengthening chemical bonds), while it had complex effects on the interfacial mixing layer—including weakening M-O bonds (M: metallic elements in IGZO), strengthening damaged Si-O bonds, and increasing O-related defects (e.g., H2O). At higher Ta, IGZO TFTs exhibited enhanced positive bias temperature stress (PBTS) stabilities but decreased negative bias temperature stress (NBTS) stabilities. The enhanced PBTS stabilities were correlated with decreased electron traps due to the stronger Si-O bonds near the interfacial layer. The decreased NBTS stabilities were related to increased electron de-trapping from donor-like defects (e.g., weak M-O bonds and H2O) in the interfacial layer. Our results suggest that although higher Ta annihilated the structural damage at the interface from ion bombardment, it introduced undesirable defects. Therefore, to comprehensively improve electrical stabilities, controlling defect generation (e.g., by using a mild sputtering condition of source/drain electrodes and oxides) was more important than enhancing defect annihilation (e.g., through increasing Ta).

Influence of Channel Surface with Ozone Annealing and UV Treatment on the Electrical Characteristics of Top-Gate InGaZnO Thin-Film Transistors.

The effect of the channel interface of top-gate InGaZnO (IGZO) thin film transistors (TFTs) on the electrical properties caused by exposure to various wet chemicals such as deionized water, photoresist (PR), and strippers during the photolithography process was studied. Contrary to the good electrical characteristics of TFTs including a protective layer (PL) to avoid interface damage by wet chemical processes, TFTs without PL showed a conductive behavior with a negative threshold voltage shift, in which the ratio of Ga and Zn on the IGZO top surface reduced due to exposure to a stripper. In addition, the wet process in photolithography increased oxygen vacancy and oxygen impurity on the IGZO surface. The photo-patterning process increased donor-like defects in IGZO due to organic contamination on the IGZO surface by PR, making the TFT characteristics more conductive. The introduction of ozone (O3) annealing after photo-patterning and stripping of IGZO reduced the increased defect states on the surface of IGZO due to the wet process and effectively eliminated organic contamination by PR. In particular, by controlling surface oxygens on top of the IGZO surface excessively generated with O3 annealing using UV irradiation of 185 and 254 nm, IGZO TFTs with excellent current-voltage characteristics and reliability could be realized comparable to IGZO TFTs containing PL.

Re-estimation of Maxwell-Wagner relaxation for novel absorbers via (Ta+Ga)-doped rutile-type TiO2 ceramics with various valence proportions and sintering temperatures

To realize next-generation capacitor materials with novel absorption properties under unconventionally severe conditions, the present study estimates the Maxwell-Wagner relaxation via investigation on (Ta+Ga) co-doped rutile-type TiO2 ceramics with changing the nominal proportions of penta-/tri-valent dopants and sintering temperatures. The key roles of Ta and Ga on resistivities in grains and grain boundaries are clarified by carefully discussing the temperature- and frequency-dependence of permittivity, Cole-Cole plots, and activation energies. It is deduced that a mean free path of charge carriers in grains is longer for a Ta-doped sample than (Ta+Ga) co-doped ones, while Ga-rich samples are more resistive. High-temperature sintering tends to result in less resistive samples due to the generation of oxygen vacancies or more active donor-like defects like Ta5+ and Ti3+ ions. For ideal Maxwell-Wagner properties on rutile-type TiO2, it is promising to optimize the conductive-core/insulative-shell structure by manufacturing Ta-rich grains and Ga-rich grain boundaries with low-temperature sintering.

Diversity Analysis of Defect Distribution and Carriers Quantization in Cu 2 ZnSnS 4/Cu2ZnSn(S,Se) 4 Kesterite Quantum Well Solar Cell

Kesterite materials, with a major advantage of direct bandgap and earth abundant material,are popular for low cost and thin film solar cell applications. Despite the popularity, the material fails to achieve significant efficiency due to the emergence of defect states during the growth process. In this paper multiple approaches have been investigated focusing on implementation of Quantum Wells(QW) to enhance the performance of solar cell. QW structure are created using CZTS x Se 1−x and Cu 2 ZnSnS 4 as QW and barrier material layers respectively. The performance evaluation of the QW solar cell is also carried out with the presence of most popular donor-like defect states in a gaussian and tail distribution way. The behavior of the device is investigated in presence of broad range of QWs from 2 to 100QWs to ensure the effect of defects on rise in QWs. The worst case performance of the solar cell is obtained to be efficiency of 9.6% under a high level of defect states. A remarkable observation on the effect of increase in number of QWs and defect states on solar cell parameters solar cell are concluded.

Intrinsic Channel Mobility Associated with Extended State Transport in IGZO TFTs

There is wide variation in the understanding of the interaction and/or independence of channel mobility and charge trapping in IGZO TFTs. A new interpretation of transport behavior proposes an intrinsic channel mobility with distinctive temperature dependence. Bottom-gate TFTs were fabricated with a 50 nm IGZO film sandwiched between a 50 nm gate oxide and a 50 nm passivation oxide layer. The working metal was molybdenum for the gate electrode and source/drain contacts. A passivation anneal was done and a capping layer was added to promote electrical stability; full process details are provided in a previous report. Devices were tested using a Lakeshore cryogenic probe station, with transfer characteristic measurements taken from room temperature to below 100 K.Electrical measurements made on long-channel devices (L = 12 µm) has revealed temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An IGZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, acceptor-like interface traps, and a temperature-dependent intrinsic channel mobility. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature. The temperature-dependent mobility follows a power-law relationship resembling behavior consistent with ionized defect scattering; the source of which is proposed. Details of the material and device model, and associated defect distribution parameters will be presented. Figure 1

Intrinsic Channel Mobility Associated with Extended State Transport in IGZO TFTs

There is wide variation in the interpretation of the interaction and/or independence of channel mobility and charge trapping in IGZO TFTs. Electrical measurements reveal temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An IGZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, and acceptor-like interface traps, thus properly regulating the amount of free channel charge. The channel mobility is defined as only a function of temperature, and reflects a thermally-activated diffusive mobility with a distinct activation energy Ea = 40 meV. This thermally activated process is clearly intrinsic, as it is constant over all bias conditions and is not dependent on the steady-state trapped charge level. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature.

Identifying and Removing the Interfacial States in Metal-Oxide-Semiconductor Schottky Si Photoanodes for the Highest Fill Factor.

A critical bottleneck for realizing an efficient Schottky type Si photoelectrode is minimizing the charge extraction losses across the heterointerface via reducing the unfavorite defects. This requires a clear microscopic insight into the correlation between interfacial features and photoconversion. Herein, by taking the n-Si/oxide (MOx)/Ni as the prototype, the heterointerface with the different characteristics and its effects on charge transportation and the corresponding photoelectric/photoelectrochemical (PEC) behaviors were clarified. An ultra-thin AlOx layer can effectively diminish the interfacial pinning of n-Si/Ni and significantly facilitate the photoconversion; meanwhile, it results in some unexpected donor-like deep defects at around 0.59 eV below the conduction band of n-Si, which could be ionized under a reverse bias and cause about 10% photogenerated charge recombination. Fortunately, these deep defects can be further eliminated by cooperating AlOx with a thin Au layer. The AlOx/Au dual-interlayer can remove almost all unexpected defects and maximize the efficiency of the electric field for charge extraction from semiconductor Si for the surface catalytic reaction. Eventually, the n-Si/SiOx/AlOx/Au/Ni/NiFeOx photoanode exhibited a record fill factor of 0.75 for the corresponding photoelectric device and an applied bias photon-to-current efficiency of 3.71% for PEC water oxidation. This study provides definite insights into interfacial electronic states and elaborates their crucial role in solar photoelectric conversion.

Study of MIS structures based on CdHgTe and HfO2 applied by PEALD

We investigate the HfO2/Hg0.78Cd0.22Te interface fabricated by plasma-enhanced atomic layer deposition (PEALD) at 120 °C During the deposition of HfO2, no donor-like defects are introduced into mercury cadmium telluride. X-ray photoelectron spectroscopy and ellipsometry were used to establish the optimal process regime at 120 °C and to demonstrate how HfO2 layer composition and growth rate per cycle depend on post-plasma purge time; the optimum is achieved at 6 s. Increasing the post-plasma purge time decreases the carbon and nitrogen impurity concentration in the HfO2 layer. Measurements of the admittance of metal-insulator-semiconductor (MIS) structures over the surface of a sample show that the electro-physical properties are uniform. We discuss the method of measuring the admittance of MIS structures that allows us to minimize the contribution of slow states with trapped charge on shape and shift of the C–V curve. The results demonstrate that the densities of fixed charge, slow states, and fast interfacial traps at the HfO2/MCT interface are greater than that for Al2O3/MCT (also formed by PEALD). The interface trap density is estimated from a normalized parallel conductance map, and the HfO2 film adheres well.

Increase in net donor concentration due to introduction of donor-like defects by ultra-low-dose Si-ion implantation and subsequent annealing in homoepitaxial n-type GaN

Si ions were implanted at a dose of 1 × 1010 cm−2 into a homoepitaxial n-type GaN layer with a net donor concentration (N D) of 3–8 × 1015 cm−3. The N D in the implanted region increased by 1–3 × 1015 cm−3 after annealing at a temperature greater than 900 °C compared with that for the as-grown homoepitaxial layer. The increase in N D was considerably larger than the peak concentration of implanted Si ions (3 × 1014 cm−3). No increase in N D was observed for an as-grown sample after annealing. These results clearly suggest that donor-like defects were introduced by implantation of Si ions and a subsequent annealing process.

Electrical and ferromagnetic properties of p-type ZnO thin films with and without the addition of graphene prepared by the sol-gel method

This study determines the effect of the addition of graphene on the electrical and ferromagnetic properties of the ZnO thin films that are prepared by the sol-gel method. ZnO is a typically oxygen-deficient metal oxide and exhibits intrinsic n-type conductivity. ZnO thin films to which graphene is added and those to which it is not, which are annealed at 500 °C for 30 min in oxygen, exhibit p-type behavior. There is an increase in the hole concentration of the graphene-doped ZnO thin film because of competition between the densities of donor-like defects such as oxygen vacancies and acceptor-like defects such as oxygen interstitials (Oi) and the defect complex that is related to the substitution of carbon for zinc (CZn) and Oi. There is ferromagnetism in a ZnO thin film at room temperature because of the presence of Oi. The intensity of the ferromagnetic signal is increased because CZn and Oi are formed in a graphene-doped ZnO thin film.

Graphene-induced positive shift of the flat band voltage in recessed gate AlGaN/GaN structures

In this work, a layer of graphene is inserted into Al2O3/recessed gate AlGaN/GaN structures to realize the positive shift of flatband voltage VFB. With a chemically inert surface and a high work function, graphene suppresses the interfacial layer growth, reduces the donor-like interface defects during the growth of Al2O3 gate dielectrics, provides a potential well to confine electrons from AlGaN and the interface defects, lifts the conduction band of GaN, leads to the disappearance of 2DEG at recessed AlGaN/GaN interface, and positively shifts VFB from 1.4 V to 5.2 V. This method provides a promising solution to fabricate E-mode AlGaN/GaN high electron mobility transistor.

Effect of plasma oxidation on tin-oxide active layer for thin-film transistor applications

In this study, the plasma oxidation effect in tin-oxide (SnOx) thin film was investigated. And on this basis, we fabricated n-type thin-film transistors (TFTs) using the SnOx thin film with the plasma oxidation by experiments. By adjusting the processing time of the oxygen plasma treatment (OPT), the optimized SnOx TFT device exhibited an extremely high field-effect mobility of 87.6 cm2 V−1 s−1, a desirable on-to-off current ratio of 1.9 × 104 and a threshold voltage of − 0.9 V. Furthermore, we investigated the origin of the performance enhancements in the n-type SnOx TFTs with the optimized OPT by introducing the density of states (DOS) modeling in TCAD simulation. The numerical simulation indicated that the attributes of donor-like Gaussian defect states (oxygen vacancies) were modified in overall DOS due to the plasma oxidation effect. These present results show that the SnOx TFT treated by oxygen plasma has great promise in the future high-performance flat panel display industries.

Back-Channel Defect Termination by Sulfur for p-Channel Cu2O Thin-Film Transistors.

The absence of a high-performance p-channel oxide thin-film transistor (TFT) is the major challenge faced in the current oxide semiconductor device technology. Simple solution-based back-channel subgap defect termination using sulfur was developed for p-channel cuprous oxide (Cu2O)-TFTs. We investigated the origin of poor device characteristics in conventional Cu2O-TFTs and clarified that it was mainly because of a back-channel donor-like defect of ∼2.8 ×1013 cm-2 eV-1, which originated from the interstitial Cu defect. Sulfur ion treatment using thiourea effectively reduced the back-channel defect down to <3 × 1012 cm-2 eV-1 and demonstrated the Cu2O-TFT with a saturation mobility of 1.38 ± 0.7 cm2 V-1 s-1, a s-value of 2.35 ± 1.22 V decade-1, and an on/off current ratio of ∼4.1 × 106. The improvement of device characteristics was attributed to the reduction of back-channel defect by the formation of a thin CuSO4 back-channel passivation layer by the chemical reaction of interstitial Cu with S and O ions. An oxide-based complementary inverter using a p-channel Cu2O-TFT and a n-channel a-In-Ga-Zn-O-TFT was demonstrated with a high voltage gain of ∼230 at VDD = 70 V.

Role of the paramagnetic donor-like defects in the high n-type conductivity of the hydrogenated ZnO microparticles

The magnetic and electronic properties of the hydrogenated highly conductive zinc oxide (ZnO) microparticles were investigated by electron paramagnetic resonance (EPR) and contactless microwave (MW) conductivity techniques in the wide temperature range. The EPR spectra simulation allowed us to resolve four overlapping EPR signals in ZnO microparticles. The Lorentzian EPR line with isotropic g-factor 1.9623(5) was related to the singly ionized oxygen vacancy. Another Lorentzian line with g|| = 1.9581(5), g⊥ = 1.9562(5) was attributed to the zinc interstitial shallow donor center, while EPR signal with g|| = 1.9567(5), g⊥ = 1.9556(5) and Gaussian lineshape was assigned to the hydrogen interstitial shallow effective-mass-like donor. The EPR signal with g|| = 1.9538(5), g⊥ = 1.9556(5) and Lorentzian lineshape was tentatively attributed to the shallow donor center. The charge transport properties in ZnO microparticles have been investigated by the contactless MW conductivity technique at T = 5–296 K. Two conduction mechanisms, including ionization of electrons from the shallow donors to the conduction band and hopping conduction process, have been distinguished. The hopping conduction process follows Mott’s variable-range hopping T−1/4 law at T = 10–100 K. The evaluated values of the average hopping distance (15.86 Å), and hopping energy (1.822 meV at 40 K) enable us to estimate the donor concentration in the investigated ZnO microparticles as ~ 1018 cm−3.

Maximize CdTe solar cell performance through copper activation engineering

Abstract The incorporation of copper (Cu) is one of the critical processes for fabricating high-efficiency CdTe thin-film solar cells. However, due to its high mobility in CdTe, the distribution and concentration of Cu must be carefully engineered to reduce the compensative donor-like interstitial defects in CdTe bulk and the recombination centers at the buffer layer/CdTe interface to maximize device performances. Here, a cuprous chloride (CuCl) solution treatment and a rapid thermal annealing (RTA) process are used to control the concentration and distribution of Cu in CdTe absorbers, enabling a champion CdTe thin-film solar cell with a power conversion efficiency of 17.5% without selenium incorporation. The results demonstrate that the use of a CuCl solution can substantially reduce the amount of Cu needed in CdTe and the RTA process is a viable approach to engineer the Cu distribution in CdTe solar cells.

Worst-Case Bias for High Voltage, Elevated-Temperature Stress of AlGaN/GaN HEMTs

The effects of high-field stress are evaluated for industrial-quality AlGaN/GaN HEMTs as a function of bias and temperature. Positive and negative threshold voltage shifts are observed, depending on stress conditions, indicating the presence of acceptor-like and donor-like traps in these devices. Worst-case transconductance degradation under rated device operating conditions is observed for devices subjected to high-voltage stress in the ON bias condition at elevated temperature. This contrasts with results on earlier-generation devices, which often show worst-case response under semi-ON bias conditions, emphasizing that each technology requires characterization under multiple bias-stress conditions. Neutral and charged oxygen donor-like DX centers and substitutional acceptor-like $\text{N}_{\mathrm{ Ga}}$ centers are the dominant defects contributing to low-frequency noise in these devices. Dehydrogenation of $\text{O}_{\mathrm{ N}}$ -H complexes during ON-bias stress and the resulting increases in densities of $\text{O}_{\mathrm{ N}}$ -related donor-like defects are evidently the reliability-limiting mechanism in these devices.

Top-Gate Amorphous Indium-Gallium-Zinc-OxideThin-Film Transistors With Magnesium Metallized Source/Drain Regions

Magnesium (Mg)-induced metallization of amorphous indium-gallium-zinc-oxide (a-IGZO) films is investigated to develop a self-aligned (SA) top-gate (SATG) a-IGZO thin-film transistor (TFT) technology. The high-conductive and SA a-IGZO source/drain (S/D) regions are well realized by a short time of sputtered deposition of Mg onto the a-IGZO film on a heated substrate, followed by the removal of the spare Mg on the surface in hot water. It is shown that the resistivity of the a-IGZO films is lowered to about $4 \times 10^{-{3}}\,\,\Omega $ cm from over $10^{{4}}~\Omega $ cm with a 36-s Mg deposition at $300~^{\circ }\text{C}$ . The metallization effect is believed to be the consequence of a large number of donor-like defects (oxygen vacancies) generated by oxidation–reduction reaction at the interface between the Mg and a-IGZO films. The SATG a-IGZO TFTs fabricated by the proposed technology show excellent electrical characteristics, such as a field-effect mobility of 19.5 cm $^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ , a subthreshold swing of 0.19 V/dec, an ON-/ OFF-current ratio of over $10^{{9}}$ , a low S/D series resistance of $2.1~\Omega $ cm, a small channel length shrinking of around $0.1~\mu \text{m}$ , and a high stability against electrical stresses.