Defect Suppression in AlN Epilayer Using Hierarchical Growth Units

Growing AlN layers remains a significant challenge because it is subject to a large volume fraction of grain boundaries. In this study, the nature and formation of the AlN growth mechanism is examined by ab initio simulations and experimental demonstration. The calculated formation enthalpies of the constituent elements, including the Al/N atom, Al–N molecule, and Al–N₃ cluster, vary with growth conditions in N-rich and Al-rich environments. Using the calculation results as bases, we develop a three-step metalorganic vapor-phase epitaxy, which involves the periodic growth sequence of (i) trimethylaluminum (TMAl), (ii) ammonia (NH₃), and (iii) TMAl+NH₃ supply, bringing in hierarchical growth units to improve AlN layer compactness. A series of AlN samples were grown, and their morphological and luminescent evolutions were evaluated by atomic force microscopy and cathodoluminescence, respectively. The proposed technique is advantageous because the boundaries and defect-related luminescence derived are highly depressed, serving as a productive platform from which to further optimize the properties of AlGaN semiconductors

Rational Design of Amorphous Indium Zinc Oxide/Carbon Nanotube Hybrid Film for Unique Performance Transistors

Here we report unique performance transistors based on sol–gel processed indium zinc oxide/single-walled carbon nanotube (SWNT) composite thin films. In the composite, SWNTs provide fast tracks for carrier transport to significantly improve the apparent field effect mobility. Specifically, the composite thin film transistors with SWNT weight concentrations in the range of 0–2 wt % have been investigated with the field effect mobility reaching as high as 140 cm²/V·s at 1 wt % SWNTs while maintaining a high on/off ratio ∼10⁷. Furthermore, the introduction SWNTs into the composite thin film render excellent mechanical flexibility for flexible electronics. The dynamic loading test presents evidently superior mechanical stability with only 17% variation at a bending radius as small as 700 μm, and the repeated bending test shows only 8% normalized resistance variation after 300 cycles of folding and unfolding, demonstrating enormous improvement over the basic amorphous indium zinc oxide thin film. The results provide an important advance toward high-performance flexible electronics applications

Rational Hydrogenation for Enhanced Mobility and High Reliability on ZnO-based Thin Film Transistors: From Simulation to Experiment

Hydrogenation is one of the effective methods for improving the performance of ZnO thin film transistors (TFTs), which originate from the fact that hydrogen (H) acts as a defect passivator and a shallow <i>n</i>-type dopant in ZnO materials. However, passivation accompanied by an excessive H doping of the channel region of a ZnO TFT is undesirable because high carrier density leads to negative threshold voltages. Herein, we report that Mg/H codoping could overcome the trade-off between performance and reliability in the ZnO TFTs. The theoretical calculation suggests that the incorporation of Mg in hydrogenated ZnO decrease the formation energy of interstitial H and increase formation energy of O-vacancy (<i>V</i>_O). The experimental results demonstrate that the existence of the diluted Mg in hydrogenated ZnO TFTs could be sufficient to boost up mobility from 10 to 32.2 cm²/(V s) at a low carrier density (∼2.0 × 10¹⁸ cm^–3), which can be attributed to the decreased electron effective mass by surface band bending. The all results verified that the Mg/H codoping can significantly passivate the <i>V</i>_O to improve device reliability and enhance mobility. Thus, this finding clearly points the way to realize high-performance metal oxide TFTs for low-cost, large-volume, flexible electronics

Effects of Nitrogen and Hydrogen Codoping on the Electrical Performance and Reliability of InGaZnO Thin-Film Transistors

Despite intensive research on improvement in electrical performances of ZnO-based thin-film transistors (TFTs), the instability issues have limited their applications for complementary electronics. Herein, we have investigated the effect of nitrogen and hydrogen (N/H) codoping on the electrical performance and reliability of amorphous InGaZnO (α-IGZO) TFTs. The performance and bias stress stability of α-IGZO device were simultaneously improved by N/H plasma treatment with a high field-effect mobility of 45.3 cm²/(V s) and small shifts of threshold voltage (<i>V</i>_th). On the basis of X-ray photoelectron spectroscopy analysis, the improved electrical performances of α-IGZO TFT should be attributed to the appropriate amount of N/H codoping, which could not only control the <i>V</i>_th and carrier concentration efficiently, but also passivate the defects such as oxygen vacancy due to the formation of stable ZnN and NH bonds. Meanwhile, low-frequency noise analysis indicates that the average trap density near the α-IGZO/SiO₂ interface is reduced by the nitrogen and hydrogen plasma treatment. This method could provide a step toward the development of α-IGZO TFTs for potential applications in next-generation high-definition optoelectronic displays

Controllable Electrical Properties of Metal-Doped In₂O₃ Nanowires for High-Performance Enhancement-Mode Transistors

In recent years, In₂O₃ nanowires (NWs) have been widely explored in many technological areas due to their excellent electrical and optical properties; however, most of these devices are based on In₂O₃ NW field-effect transistors (FETs) operating in the depletion mode, which induces relatively higher power consumption and fancier circuit integration design. Here, n-type enhancement-mode In₂O₃ NW FETs are successfully fabricated by doping different metal elements (Mg, Al, and Ga) in the NW channels. Importantly, the resulting threshold voltage can be effectively modulated through varying the metal (Mg, Ga, and Al) content in the NWs. A series of scaling effects in the mobility, transconductance, threshold voltage, and source–drain current with respect to the device channel length are also observed. Specifically, a small gate delay time (0.01 ns) and high on-current density (0.9 mA/μm) are obtained at 300 nm channel length. Furthermore, Mg-doped In₂O₃ NWs are then employed to fabricate NW parallel array FETs with a high saturation current (0.5 mA), on/off ratio (>10⁹), and field-effect mobility (110 cm²/V·s), while the subthreshold slope and threshold voltage do not show any significant changes. All of these results indicate the great potency for metal-doped In₂O₃ NWs used in the low-power, high-performance thin-film transistors

Rational Design of ZnO:H/ZnO Bilayer Structure for High-Performance Thin-Film Transistors

The intriguing properties of zinc oxide-based semiconductors are being extensively studied as they are attractive alternatives to current silicon-based semiconductors for applications in transparent and flexible electronics. Although they have promising properties, significant improvements on performance and electrical reliability of ZnO-based thin film transistors (TFTs) should be achieved before they can be applied widely in practical applications. This work demonstrates a rational and elegant design of TFT, composed of poly crystalline ZnO:H/ZnO bilayer structure without using other metal elements for doping. The field-effect mobility and gate bias stability of the bilayer structured devices have been improved. In this device structure, the hydrogenated ultrathin ZnO:H active layer (∼3 nm) could provide suitable carrier concentration and decrease the interface trap density, while thick pure-ZnO layer could control channel conductance. Based on this novel structure, a high field-effect mobility of 42.6 cm² V^–1 s^–1, a high on/off current ratio of 10⁸ and a small subthreshold swing of 0.13 V dec^–1 have been achieved. Additionally, the bias stress stability of the bilayer structured devices is enhanced compared to the simple single channel layer ZnO device. These results suggest that the bilayer ZnO:H/ZnO TFTs have a great potential for low-cost thin-film electronics

Rational Design of Sub-Parts per Million Specific Gas Sensors Array Based on Metal Nanoparticles Decorated Nanowire Enhancement-Mode Transistors

“One key to one lock” hybrid sensor configuration is rationally designed and demonstrated as a direct effective route for the target-gas-specific, highly sensitive, and promptly responsive chemical gas sensing for room temperature operation in a complex ambient background. The design concept is based on three criteria: (i) quasi-one-dimensional metal oxide nanostructures as the sensing platform which exhibits good electron mobility and chemical and thermal stability; (ii) deep enhancement-mode field-effect transistors (E-mode FETs) with appropriate threshold voltages to suppress the nonspecific sensitivity to all gases (decouple the selectivity and sensitivity away from nanowires); (iii) metal nanoparticle decoration onto the nanostructure surface to introduce the gas specific selectivity and sensitivity to the sensing platform. In this work, using Mg-doped In₂O₃ nanowire E-mode FET sensor arrays decorated with various discrete metal nanoparticles (i.e., Au, Ag, and Pt) as illustrative prototypes here further confirms the feasibility of this design. Particularly, the Au decorated sensor arrays exhibit more than 3 orders of magnitude response to the exposure of 100 ppm CO among a mixture of gases at room temperature. The corresponding response time and detection limit are as low as ∼4 s and ∼500 ppb, respectively. All of these could have important implications for this “one key to one lock” hybrid sensor configuration which potentially open up a rational avenue to the design of advanced-generation chemical sensors with unprecedented selectivity and sensitivity