Density Of Deep Level Defects Research Articles

Study on the vertical Bridgman method of melt-grown CsPbBr3 single crystals for nuclear radiation detection.

As an excellent representative of all-inorganic perovskite materials, CsPbBr3 has been widely used in high-energy rays or high-energy particles detection for its outstanding high carrier mobility and long diffusion length. The great challenges and opportunities in these fields are crystal growth technology, especially the high-quality and large-sized CsPbBr3 single crystals. In this work, the influences of growth parameters (temperature gradient, growth rate, cooling rate) and thermal stress by the vertical Bridgman method on the quality and performance of CsPbBr3 crystals are systematically studied. The final results show that 10°C cm-1 is the optimized temperature gradient and 0.5 mm h-1 is the suitable growth rate for CsPbBr3 crystal growth. The study also shows that a cooling rate of 10°C h-1 for the general temperature interval and 1°C h-1 for the phase transition temperature interval is helpful to balance crystal growth efficiency as well as crystal quality. Crystal cracks caused by thermal stress as well as crystal adhesion on the ampoule can be effectively solved by depositing a uniform carbon film on the ampoule in advance. The optical, electrical and detection performance are also investigated. The optical characterization in the wavelength region ranging from ultraviolet to infrared indicates the crystal has a low density of deep-level defects and good crystal quality. The resistivity over 109 Ω cm and μτ of electrons over 10-2 cm-2 V-1 proves that the electrical performance of the crystal has met the basic requirement for nuclear radiation detection. The metal-semiconductor-metal structure Ti/Ni/CsPbBr3/Ni/Ti detector fabricated from the optimized CsPbBr3 single crystal has an energy resolution of 12.85% (137Cs, 662 keV). The purpose of this work is to provide a useful guide and reference for the future exploration of repeatable and improvable CsPbBr3 crystal growth technology.

Sulfur-graded kesterite structured film drives improvement of VOC.

Realizing the graded bandgap in absorber layer is very essential for high efficient thin film solar cells. However, such bandgap modification in kesterite-structured Cu2ZnSnSe4 is normally realized via high temperature sulfurization process (above 500°C), which is not only difficult to control the sulfurization depth, but also introduces additional deep defects because of the decomposition of absorber layer at such high temperature. In this study, a low-temperature sulfurization process (150°C) is developed. Such process not only inhibits the decomposition of Cu2ZnSnSe4 films and controls the elemental distribution very well, but also increase the surface bandgap of the absorber layer and form a gradient energy bandgap. Also, the density of deep-level defects in the Cu2ZnSnSe4 layer is reduced. As a consequence, the open circuit voltage of the solar cell is improved by 60 mV. This study paves the way towards the high efficient kesterite solar cell and other solar cells.

Self-assembled monolayers as hole transport layers for efficient thermally evaporated blue perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) based on thermal evaporation technique have demonstrated great potential in newly-developed wide color gamut display applications. However, it is still a challenging task to obtain high efficiency thermally evaporated blue PeLEDs. One of the key issues is the lack of desirable functional materials with both hole transport function and perovskite buried interface modification function, which can alleviate the accumulation of high density of deep-level defects between hole transport layer (HTL) and perovskite emitting layer (EML) and weaken the interfacial nonradiative recombination process. In this study, we developed a new multifunctional wide-bandgap self-assembled monolayers (SAMs) suitable for thermally evaporated blue PeLEDs, named (2-(3-bromo-6-(4-formylphenyl)-9H-carbazol-9-yl)ethyl)phosphonic acid (CZPC). The interactions between the carbonyl groups (C = O) contained in CZPC and uncoordinated Pb2+ are critical for improving crystallinity and suppressing nonradiative losses at the buried perovskite-hole transporter interface. In addition, the phosphonic acid groups bonding with indium tin oxide (ITO) can form a self-assembled monolayer to facilitate carrier injection and transport. Finally, simplified thermally evaporated sky-blue (488 nm) PeLEDs utilize CZPC as HTL and no additional functional layers such as hole injection layer are used show excellent device performance with a maximum external quantum efficiency (EQE) of 5.42 %, accompanied by the CIE color coordinates of (0.07, 0.25) and a full width at half maximum (FWHM) of 24 nm. This work lays a foundation for the further exploration of SAMs on high-performance thermally evaporated blue PeLEDs towards ultra-high resolution display applications.

Influence of trap-assisted and intrinsic Auger–Meitner recombination on efficiency droop in green InGaN/GaN LEDs

We study the impact of deep-level defects on trap-assisted Auger–Meitner recombination in c-plane InGaN/GaN LEDs using a small-signal electroluminescence (SSEL) method and deep-level optical spectroscopy (DLOS). Carrier dynamics information, including carrier lifetime, recombination rate, and carrier density, is obtained from SSEL, while DLOS is used to obtain the deep-level defect density. Through fitting the nonradiative recombination rates of wafers with different deep-level defect densities, we obtain the Shockley–Read–Hall (SRH) and trap-assisted Auger–Meitner recombination (TAAR) coefficients. We show that defect-related nonradiative recombination, including both SRH and TAAR, accounts for a relatively small fraction of the total nonradiative recombination, which is dominated by intrinsic Auger–Meitner recombination. The interplay between carrier localization and Coulomb enhancement has a different impact on radiative and intrinsic Auger–Meitner recombination. Evidence is presented that the imbalance between the change of radiative and intrinsic Auger–Meitner recombination is the primary cause of the efficiency droop at high carrier densities in the samples studied.

Quantitative analysis of defect states in InGaZnO within 2 eV below the conduction band via photo-induced current transient spectroscopy

This work investigates the function of the oxygen partial pressure in photo-induced current measurement of extended defect properties related to the distribution and quantity of defect states in electronic structures. The Fermi level was adjusted by applying a negative gate bias in the TFT structure, and the measurable range of activation energy was extended to < 2.0 eV. Calculations based on density functional theory are used to investigate the changes in defect characteristics and the role of defects at shallow and deep levels as a function of oxygen partial pressure. Device characteristics, such as mobility and threshold voltage shift under a negative gate bias, showed a linear correlation with the ratio of shallow level to deep level defect density. Shallow level and deep level defects are organically related, and both defects must be considered when understanding device characteristics.

Sb2 Se3 Thin-Film Solar Cells Exceeding 10% Power Conversion Efficiency Enabled by Injection Vapor Deposition Technology.

Binary Sb2 Se3 semiconductors are promising as the absorber materials in inorganic chalcogenide compound photovoltaics due to their attractive anisotropic optoelectronic properties. However, Sb2 Se3 solar cells suffer from complex and unconventional intrinsic defects due to the low symmetry of the quasi-1D crystal structure resulting in a considerable voltage deficit, which limits the ultimate power conversion efficiency (PCE). In this work, the creation of compact Sb2 Se3 films with strong [00l] orientation, high crystallinity, minimal deep level defect density, fewer trap states, and low non-radiative recombination loss by injection vapor deposition is reported. This deposition technique enables superior films compared with close-spaced sublimation and coevaporation technologies. The resulting Sb2 Se3 thin-film solar cells yield a PCE of 10.12%, owing to the suppressed carrier recombination and excellent carrier transport and extraction. This method thus opens a new and effective avenue for the fabrication of high-quality Sb2 Se3 and other high-quality chalcogenide semiconductors.

Numerical analysis of a novel HTL-free perovskite solar cell with gradient doping and a WS₂ interlayer

Lead Halide Perovskite Solar Cells have exhibited the highest efficiencies for Perovskite Solar Cells. As a result of its affordable processing costs, and stability, HTL-free PSCs have grown in popularity in recent years. A comprehensive numerical study of a novel HTL-free PSC, with a structure of FTO/ZnO/WS₂/CH₃NH₃PbI₃/Au, is reported in this article. Multiple factors that affect the performance of the solar cell have been thoroughly investigated like absorber thickness, doping density and deep level defect density. Also, the influence of the interface defects has been closely studied. Finally, the impact of a gradient doping concentration on the performance parameters has been analyzed. After optimization, we have obtained the final simulated device parameters of power conversion efficiency(PCE) of 26.25%, with an open-circuit voltage(Voc) of 1.20 ​V, a short-circuit current(Jsc) of 24.60 ​mA/cm2, and a Fill Factor(FF) of 89.04%, which is an improvement on the best values recorded in literature.

Quasi-Vertically Oriented Sb2Se3 Thin-Film Solar Cells with Open-Circuit Voltage Exceeding 500 mV Prepared via Close-Space Sublimation and Selenization.

Sb2Se3, one of the most desirable absorption materials for next-generation thin-film solar cells, has an excellent photovoltaic characteristic. The [hk1]-oriented (quasi-vertically oriented) Sb2Se3 thin film is more beneficial for promoting efficient carrier transport than the [hk0]-oriented Sb2Se3 thin film. Controlling thin-film orientation remains the main obstacle to the further improvement in the efficiency of Sb2Se3-based solar cells. In this work, the controlled [hk0] or [hk1] orientation of the Sb2Se3 precursor is readily adjusted by tuning the substrate temperature and the distance between the source and the sample in close-space sublimation (CSS). Well-crystallized stoichiometric Sb2Se3 thin films with the desired orientation and large crystal grains are successfully prepared after selenization. Sb2Se3 thin-film solar cells in a substrate configuration of glass/Mo/Sb2Se3/CdS/ITO/Ag are fabricated with a power conversion efficiency of 4.86% with a record open-circuit voltage (VOC) of 509 mV. The significant improvement in VOC is closely related to the quasi-vertically oriented Sb2Se3 absorber layer with reduced deep-level defect density in the bulk and defect passivation at the Sb2Se3/CdS heterojunction. This work indicates that CSS and selenization show a remarkable potential for the fabrication of high-efficiency Sb2Se3 solar cells.

Quantitative analysis of defect states in amorphous InGaZnO thin-film transistors using photoinduced current transient spectroscopy

The device and defect characteristics of amorphous indium–gallium–zinc oxide (In:Ga:Zn = 1:1:1 at.%) thin-film transistors (TFTs) as a function of the oxygen partial pressure were investigated. It was found that as the oxygen partial pressure increased, the field effect mobility decreased, the threshold voltage saw a positive shift, and this shift of threshold voltage increased under a negative gate bias stress. From our qualitative analysis of defect states below the conduction band, it was found that as the oxygen partial pressure increased, defect states in the shallow levels decreased, while defect states in the deep levels increased. A quantitative analysis of the defect states in the TFT structures was conducted using photoinduced current transient spectroscopy. It was found that as the oxygen partial pressure used during fabrication of the TFTs increased from 0% to 10% to 60%, the defect states in the shallow levels decreased from 2.74 × 1018 to 2.93 × 1017 to 3.55 × 1016 cm−3, while the defect states in the deep levels increased from non-availability to 1.86 × 1016 to 3.25 × 1016 cm−3. As the oxygen partial pressure increased, the decrease in shallow level defect density is strongly related to a decrease in carrier concentration; the increase in deep level defect density affects the mobility and causes device instability.

High-efficiency ultra-thin Cu2ZnSnS4 solar cells by double-pressure sputtering with spark plasma sintered quaternary target

In recent years, Cu2ZnSnS4 (CZTS) semiconductor materials have received intensive attention in the field of thin-film solar cells owing to its non-toxic and low-cost elements. In this work, double-pressure sputtering technology is applied to obtain highly efficient and ultra-thin (~450 nm) pure Cu2ZnSnS4 (CZTS) solar cell. Using mixed materials with sulfides and copper powder as a quaternary target via spark plasma sintering (SPS) method and adopting double-layer sputtering (high + low pressure), a highly adhesive and large-grained CZTS thin film is achieved. As a result, the damage to the surface of Mo contact is decreased so that the reflectivity of incident light can be improved. Moreover, the composition of CZTS film was more uniform and the secondary phase separation at the Mo interface was reduced. Therefore, the interface defect state and deep level defect density in corresponding device with double-pressure is reduced and the ratio of depletion thickness to absorption layer thickness can reached to 0.58, which promoted the collection of photogenerated carriers. Finally, an efficiency of 9.3% for ultra-thin (~450 nm) CZTS film solar cell is obtained.

Overview of Ge-incorporated kesterite solar cells

<p indent=0mm>Kesterite (CZTS(e)) solar cell has attracted tremendous interest for its feature: Earth-abundant composition, convenient fabrication process, environmental friendliness and low cost. However, the severe large voltage deficient in CZTS(e) solar cell remains a challenge for further enhancement of the power conversion efficiency (PCE). In this prospect, three mechanisms are proposed: Cu/Zn disorder, potential interfacial losses and Sn-related deep-level defects. Sn-related deep-level defects are the most detrimental and hardest factor to manipulate due to the low energy of the formation of atomic antisite and multivalency nature of Sn. Adding extrinsic elements into the absorber layer is of an important method to passivate Sn-related defects. Among them, incorporation of Ge (CZTS:Ge) shows great potential. Comparing to Sn, Ge is more likely to be stabilized at +4 oxidation state. DFT calculation suggests that the deep-level defect density of <sc>CZTS(e):Ge</sc> is much smaller than that of CZTS(e). The maximum trap-limited conversion efficiency can be promoted to 24.1% with Ge incorporation compared with 20.9% in intrinsic CZTS(e). Early works show that CZTS(e):Ge solar cells present relative higher <italic>V</italic>_oc and has reached 12.3% power conversion efficiency (PCE), promising to champion the efficiency of CZTS(e) solar cell. Up to date, the benefits from Ge incorporation can be summarized in three aspects. First, Ge incorporation can induce the formation of Ge-Se low-temperature liquid phase as crystallization flux during annealing, which finally enlarges grain size and promote morphology. In the meantime, Sn-Se phases formation can be minimized through a modified reaction pathway brought by Ge doping. Second, Sn-related deep-level defects experimentally observed will be passivated when Ge is incorporated. Third, the energy difference between kesterite, stannite and primitive mixed CuAu is enlarged in Cu₂ZnGeS₄, indicating that Ge may stabilize kesterite in absorber and suppress band tailing caused by atomic disorder (or phase instability). To break through current efficiency bottleneck of CZTS(e) solar cells, we prospect the futural directions in constructing CZTS(e):Ge. First, Zn composition in absorber should be handled with great care to suppress the formation of Ge_Zn-Cu_Zn further. Next, modulation of the gradient band gap, achieved by vertical Ge-Sn compositional gradient in absorber, is also an important aspect. How to avoid the fast diffusion of Ge to form the vertical Ge-Sn gradient will be of the most essential question. Vertical control of independent Sn composition or Ge incorporation in the post-selenization process may be two potential solutions. Furthermore, the nature of the wide band gap of pure sulfide CZTS(e):Ge makes itself suitable to fabricate the top cell in tandem solar cell. Finally, interface modifications and band engineering in CZTS(e) solar cells will also benefit in constructing CZTS(e):Ge solar cells.

Enhancing the open circuit voltage of the SnS based heterojunction solar cell using NiO HTL

In this article, the numerical investigations on a novel (ITO/CeO2/SnS/NiO/Mo) heterostructure of the SnS-based solar cell have been presented using SCAPS-1D simulation software. The main objective of the study was the exploration of the effect of NiO hole transport layer (HTL) on the performance of the proposed SnS-based heterojunction solar cell. The open circuit voltage of the proposed cell has been enhanced up to 345 mV after using NiO HTL which indicates a significant reduction of surface recombination velocity at SnS/electrode interface. Around 12.78% efficiency enhancement was observed after using NiO HTL in the SnS-based heterojunction solar cell, and an efficiency of 25.1% could be obtained from the proposed heterojunction solar cell. It was found that the cell performance depended on the carrier concentration and thickness of the CeO2 electron transport layer (ETL), SnS absorber layer, and NiO HTL, respectively. The effects of deep level defect density of the SnS absorber layer and interface defect density of NiO/SnS and CeO2/SnS on the cell performance ware also studied. These findings reveal that the NiO could be a promising HTL for the fabrication of low cost, high-efficiency SnS-based heterojunction solar cell.

Hydrophobic effect evolution dependent manipulation of ZnO nanostructures morphology

The morphologies of different ZnO nanostructures (ZNSs) films (deposited on glass substrates) are investigated using simple and low-cost techniques. Two synthesis techniques, i.e., direct hydrothermal technique and a combination of pulsed-laser ablation under liquid and hydrothermal (PLAL-H) technique, are employed. The first technique (direct hydrothermal technique) is used to fabricate three-dimensional (3D) flower-like ZNSs and one-dimensional (1D) solid rod- along with enclosed tube-like ZNSs under different pH conditions/values. Moreover, a zero-dimensional (0D) ZnO nanoparticles (ZNPs)-based film is prepared by PLAL-H technique. The influence of tuning morphology of ZNSs films on the hydrophobic effect is examined by XRD, FE-SEM, and photoluminescence (PL). XRD patterns confirmed the polycrystalline structures of ZNSs films. FE-SEM explored the morphology transformation from 3D flower-like to 1D solid rod- and enclosed tube-like ZNSs films by varying the pH values from 10.5 to 5.7. The PL spectra revealed a higher surface area and deep-level defect density related to the ZnO morphology. Depending on the surface contact angle measurements, the hydrophobic performance of flower-like ZNSs is much superior than 1D solid rod-like, enclosed tube-like, and 0D ZNPs films. The super-hydrophobic effect of flower-like ZnO is attributed to the synergism of regular formed and higher density of ZNSs. Therefore, it is inferred that the successful controllable morphology of ZNSs film under mild deposition conditions could play a crucial role to get a superior hydrophobic behavior of ZNSs film.

Sputtered and selenized Sb2Se3 thin-film solar cells with open-circuit voltage exceeding 500 mV

Antimony selenide (Sb 2 Se 3 ) is a potential absorber material for environment-friendly and cost-efficient photovoltaics and has achieved considerable progress in recent years. However, the severe open-circuit voltage ( V oc ) deficit ascribed to the interface and/or bulk defect states has become the main obstacle for further efficiency improvement. In this work, Sb 2 Se 3 absorber layer was prepared by an effective combination reaction involving sputtered and selenized Sb precursor thin films. The self-assembled growth of Sb 2 Se 3 thin films with large crystal grains, benign preferential orientation, and accurate chemical composition were successfully fulfilled under an appropriate thickness of Sb precursor and an optimized selenization scenario. Substrate structured Sb 2 Se 3 thin-film solar cells, a champion device with a power-conversion efficiency of 6.84%, were fabricated. This device is comparable to state-of-the-art ones and represents the highest efficiency of sputtered Sb 2 Se 3 solar cells. Importantly, the high V oc of 504 mV is closely related to the reduced deep level defect density for the Sb 2 Se 3 absorber layer, the passivated interfacial defects for Sb 2 Se 3 /CdS heterojunction interface, and the additional heterojunction heat treatment-induced Cd and S inter-diffusion. This significantly improved V oc demonstrates remarkable potential to broaden its scope of applications for Sb 2 Se 3 solar cells. • An effective combination reaction of sputtered and selenized Sb precursors for Sb 2 Se 3 thin film solar cells. • The self-assembled growth of Sb 2 Se 3 thin films with large crystal grains, benign preferential orientation and accurate chemical composition. • A highly interesting V oc record of 504 mV obtained due to the reduced deep level defect density, the passivated interfacial defects and heterojunction heat treatment-induced Cd and S inter-diffusion. • PCE of 6.84% represents the highest efficiency of sputtered Sb 2 Se 3 solar cells.

Perceiving of Defect Tolerance in Perovskite Absorber Layer for Efficient Perovskite Solar Cell

Controlling the defect in the perovskite absorber layer is a very crucial issue for developing highly efficient and stable perovskite solar cells (PSCs) as it exhibits the existence of unavoidable defects even after the careful fabrication process. In this study, the presence of defects in the perovskite layer has been evaluated through the analysis of its structural and optical properties. Then the investigations on the impact of defect density on perovskite absorber layer and its associated solar cell parameters have been carried out by numerical simulation utilizing SCAPS-1D software. Besides the defect density, the thickness of the absorber layer has also been varied to find optimum values of cell parameters. It has been found that when the thickness of absorber and shallow defect density is increased from 200 nm to 800 nm and 1 × 10 13 cm -3 to 1 × 10 18 cm -3 respectively, power conversion efficiency (PCE) is varied from 26.7% to 0.90%. However, when the thickness and deep defect density are raised from 200 nm to 800 nm and 1 × 10 13 cm -3 to 1 × 10 16 cm -3 , respectively, the PCE is varied from 19.3% to 6.15%. It is revealed that optimum absorber thickness is 550 nm and the tolerances of shallow level and deep level defect density are 1 × 10 17 cm -3 and 1 × 10 15 cm -3 , respectively.

Study on the role of growth time on structural, morphological and optical properties of un-capped and L-cyst.-capped ZnO nanorods grown on a GZO seeded thin film layer from an aqueous solution

The influence of the deposition time (ranging from 30 to 300 min) and the role of l-cysteine on the structural and optical properties of the un-capped and L-cyst.-capped ZnO nanorods (ZNRs) grown using the chemical bath deposition method was discussed. X-ray diffraction patterns showed that the estimated crystallite size increased with the deposition time up to 240 min for both capped and un-capped samples, while the calculated strain was found to decrease to a minimum for the 240 min deposition time. The Fourier transform infra-red spectroscopy of the as-grown ZNRs films showed various absorption bands in the range of 250–4000 cm-1 indicating the presence of different functional groups. Scanning electron microscopy analysis illustrated that the aspect ratios of the L-cyst.-capped ZNRs increased six-fold as the growth duration varied from 30 to 240 min, but decreased slightly at longer growth time. The root mean square roughness increased continuously from 10.9 to 36.3 nm as the growth time was raised from 30 to 240 min for the un-capped ZNRs. The samples deposited at 240 min exhibited the highest photoluminescence emission intensity ratios suggesting a low density of deep level defects. An inverse relation between the optical band gaps and growth time was observed. The highly luminescent cyst.-capped sample, with well-aligned nanorods and highest aspect ratio and good crystallization grown at 240 min growth time can be used as a possible photoanode component of dye-sensitized solar cells.

Effect of deep-level defect density of the absorber layer and n/i interface in perovskite solar cells by SCAPS-1D

In this paper, Solar Cell Capacitance Simulator-1D (SCAPS-1D) was used to study the absorber layer defect density and n/i interface of perovskite solar cells versus various cell thickness values. The planar p-i-n structure was defined as PEDOT:PSS/Perovskite/CdS, and its performance was simulated. Power conversion efficiency >25% can be achieved at <1014 cm−3 defect density and >400 nm thickness of absorber layer, respectively. The study assumed 0.6 eV Gaussian defect energy level below the perovskite’s conduction band with a characteristic energy of 0.1 eV. These conditions resulted in an identical outcome on the n/i interface. These results show constraints on numerical simulation for correlation between defect mechanism and performance.

Efficient Anti-solvent-free Spin-Coated and Printed Sn-Perovskite Solar Cells with Crystal-Based Precursor Solutions

Summary Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.

Density of defect states retrieved from the hysteretic gate transfer characteristics of monolayer MoS2 field effect transistors

Defect states play an important role in low-dimensional semiconductor devices. However, it becomes increasingly challenging to find the density of defect states for ultra-scaled devices using traditional capacitive techniques such as capacitance-voltage (CV) method and deep level transient spectroscopy (DLTS). Here, we proposed a model to quantitatively retrieve the density of defect states from the hysteretic gate transfer characteristics of field effect transistors (FETs), and applied it to monolayer MoS2 FETs before and after superacid treatment. We found that the superacid treatment significantly reduced the density of deep level defects. As a result, the photoluminescence was enhanced 19 folds due to the suppression of non-radiative recombination via deep level defects.

TiN/Al2O3/ZnO gate stack engineering for top-gate thin film transistors by combination of post oxidation and annealing

Control of fabrication processes for a gate stack structure with a ZnO thin channel layer and an Al2O3 gate insulator has been examined for enhancing the performance of a top-gate ZnO thin film transistor (TFT). The Al2O3/ZnO interface and the ZnO layer are defective just after the Al2O3 layer formation by atomic layer deposition. Post treatments such as plasma oxidation, annealing after the Al2O3 deposition, and gate metal formation (PMA) are promising to improve the interfacial and channel layer qualities drastically. Post-plasma oxidation effectively reduces the interfacial defect density and eliminates Fermi level pinning at the Al2O3/ZnO interface, which is essential for improving the cut-off of the drain current of TFTs. A thermal effect of post-Al2O3 deposition annealing at 350 °C can improve the crystalline quality of the ZnO layer, enhancing the mobility. On the other hand, impacts of post-Al2O3 deposition annealing and PMA need to be optimized because the annealing can also accompany the increase in the shallow-level defect density and the resulting electron concentration, in addition to the reduction in the deep-level defect density. The development of the interfacial control technique has realized the excellent TFT performance with a large ON/OFF ratio, steep subthreshold characteristics, and high field-effect mobility.