Lingxiang Chen

p-type behavior in In–N codoped ZnO thin films

p-type ZnO thin films have been realized by the In–N codoping method. Secondary ion mass spectroscopy revealed that the nitrogen incorporation was enhanced by the presence of indium in ZnO. The as-grown In–N codoped ZnO film shows acceptable p-type behavior at room temperature with high film quality. A conversion from p-type conduction to n type in a range of temperature was confirmed by Hall effect measurement. The lowest reliable room-temperature resistivity was found to be 3.12Ωcm with a carrier concentration of 2.04×1018cm−3 and a Hall mobility of 0.979cm2V−1S−1. The p-type behavior is stable.

ZnO light-emitting diodes fabricated on Si substrates with homobuffer layers

ZnO homojunction light-emitting diodes (LEDs), comprised of N–Al codoped p-type ZnO and Al-doped n-type ZnO layers, were fabricated on Si substrates with homobuffer layers. The current-voltage measurements showed typical diode characteristic with a threshold voltage of about 3.3V. The electroluminescence (EL) bands at 110K consisted of a near-band-edge emission at 3.18eV and a deep level emission at 2.58eV. The EL emissions were assigned as radiative recombinations, presumably of donor-acceptor pairs, in the p-type layer of the LED. The quenching of EL with temperature was attributed to the degradation of p-type conducting of the ZnO:(N,Al) layer.

Characterization of amorphous Si-Zn-Sn-O thin films and applications in thin-film transistors

Amorphous silicon-zinc-tin-oxide (α-SZTO) thin films were prepared, and their properties were investigated physically and electrically, with an emphasis on the Si effects. An appropriate Si content in the matrix can not only achieve stable and dense films, but also suppress the formation of oxygen vacancies efficiently, due to its high oxygen bonding ability. Thin film transistors (TFTs) with α-SZTO active channel layers exhibited a field-effect mobility of around 1 cm2V−1s−1, an on/off current ratio of 107, and a subthreshold swing of 0.863 V/decade with a good long-term stability. The α-SZTO TFT is a potential candidate for electronic applications.

Stability of amorphous InAlZnO thin-film transistors

The stability of thin-film transistors (TFTs) with amorphous InAlZnO (a-IAZO) thin films as the channel layers was investigated. The devices annealed at 300 °C had a large threshold voltage (Vth) shift under gate voltage sweep, while the devices annealed at 400 °C were quite stable. The S value of the transfer characteristic curve was effectively reduced after 400 °C annealing as compared to 300 °C annealing. X-ray photo-electron spectroscopy results also showed oxygen deficiencies decreased as the annealing temperature increased. The improvement of TFTs stability might attribute to the reduction of trap states related to oxygen deficiencies. The 400 °C annealed a-IAZO TFTs exhibited small positive shift of threshold voltages under bias stress conditions, suggesting the a-IAZO might be a promising candidate for application in TFTs.

Photoluminescence in heavily doped ZnO:N:In films

Temperature-dependent photoluminescence is used to investigate ZnO films codoped with In and N at different doping levels. Conversion from exciton recombination to band-to-band transition with increasing both doping level and temperature is observed. We suggest that ionization of the N acceptors and dissociation of excitons by impurity-induced local field are responsible for such conversion. For the film with N concentration of 4×1020cm−3, the excitonic emission intensity shows anomalous temperature dependence due to localized carriers. The localization energy and the N acceptor level is determined to be about 5 and 164meV, respectively.

High-Performance GaN-Based LEDs With AZO/ITO Thin Films as Transparent Contact Layers

The Al-doped ZnO (AZO)/indium tin oxide (ITO) bilayer films were proposed as transparent contact layers (TCLs) for the fabrication of GaN-based light-emitting diodes (LEDs). In TCLs on the p-type GaN layer, the ITO film serves as the ohmic contact layer with the thickness of only 20 nm, whereas the 300–750nm AZO films act as the current spreading layer. At an optimal AZO thickness of 500 nm, GaN-based LEDs with AZO/ITO TCLs have a forward voltage of 3.36 V, an electroluminescence emission at 526 nm with highest brightness and a large light intensity of 386 mcd at 20 mA, which are almost the same as the commercial LEDs with a 300-nm ITO TCL. The 500-nm AZO/20-nm ITO bilayer films exhibit a high transparency above 90% in the visible region, but they display a low conductivity with resistivity

Thin-Film Transistors Based on Amorphous ZnNbSnO Films With Enhanced Behaviors

\sim 7 \times 10^{-3}~\Omega \cdot

Annealing Treatment on Amorphous InAlZnO Films for Thin-Film Transistors

cm. The success of GaN-based LEDs with such a relatively high-resistivity electrode strongly demonstrates that the AZO/ITO film is a very effective and practical TCL on the p-type GaN layer. The indium-saving AZO/ITO TCLs may be actually a universal approach as p-type electrodes in high-performance GaN-based LEDs for commercially mass production with low cost.

Ultrathin amorphous ZnGexSnO films for high performance ultra-thin-film transistors

Amorphous zinc-niobium-tin-oxide (a-ZNTO), a new amorphous oxide semiconductor, was proposed for fabricating thin-film transistors (TFTs). a-ZNTO thin films were grown by magnetron sputtering and used as channel layers of TFTs. The effects of niobium content on film properties and device behaviors were investigated in detail. Nb could serve as a carrier suppressor by reducing oxygen vacancies in a-ZNTO films and lower the interfacial trap states in a-ZNTO TFTs. The enhanced performances of a-ZNTO TFTs were achieved at an optimized Nb content of x=0.2 for a Nb:Zn:Sn atomic ratio of x:4:7. The reduced channel sizes are very effective to improve TFT performances, with an ON/OFF current ratio of ~ 108 and a field-effect mobility of 13.2 cm2/Vs. The indium-free a-ZNTO TFTs may have the potential for applications in next-generation displays.

Influence of post-annealing temperature on properties of ZnO:Li thin films

Amorphous InAlZnO (a-IAZO) films were grown by pulsed laser deposition at room temperature and annealed at various temperatures. The amorphous state of a-IAZO films is thermally stable at high temperatures up to 700 °C. The films exhibit a high visible transmittance above 95% and an appropriate resistivity on the order of 106 Ω · cm. As the annealing temperature increases, the optical bandgap and resistivity decrease in general. The microcracks form in films at an annealing temperature above 500 °C. The a-IAZO films annealed at 400 °C are suitable for channel layers of thin-film transistors (TFTs) and the devices demonstrate good performances with an on/off ratio of 108 and field-effect mobility of 2.2 cm2 · V-1 · s-1. The observations will provide useful physical insight into film properties and also offer basic design guideline for a-IAZO TFTs.