Kashif Javaid

Semiconducting ZnSnN2 thin films for Si/ZnSnN2 p-n junctions

ZnSnN2 is regarded as a promising photovoltaic absorber candidate due to earth-abundance, non-toxicity, and high absorption coefficient. However, it is still a great challenge to synthesize ZnSnN2 films with a low electron concentration, in order to promote the applications of ZnSnN2 as the core active layer in optoelectronic devices. In this work, polycrystalline and high resistance ZnSnN2 films were fabricated by magnetron sputtering technique, then semiconducting films were achieved after post-annealing, and finally Si/ZnSnN2 p-n junctions were constructed. The electron concentration and Hall mobility were enhanced from 2.77 × 1017 to 6.78 × 1017 cm−3 and from 0.37 to 2.07 cm2 V−1 s−1, corresponding to the annealing temperature from 200 to 350 °C. After annealing at 300 °C, the p-n junction exhibited the optimum rectifying characteristics, with a forward-to-reverse ratio over 103. The achievement of this ZnSnN2-based p-n junction makes an opening step forward to realize the practical application of the...

Threshold Voltage Tuning in a-IGZO TFTs With Ultrathin SnO x Capping Layer and Application to Depletion-Load Inverter

Tunable threshold voltage of a thin-film transistor (TFT) is highly desirable for designing multifunctional electronic circuits. In this letter, an ultrathin SnOx capping layer was adopted to modify the threshold voltage of bottom-gate amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs. A threshold voltage shift from 15.2 to -9.0 V was observed as the SnOx thicknesses increased from 0 to 19 nm, accompanying by a sizable increase of the intrinsic electron concentration in the channel layer. It was believed that the SnOx capping layer can extract loosely bound oxygen from the a-IGZO, which was supported by the SnOx composition variation with its thickness. Combining an uncovered a-IGZO TFT with a SnOx capped a-IGZO TFT, an enhancement/depletion inverter with a voltage gain of up to 45.9 was successfully demonstrated.

Extended-gate-type IGZO electric-double-layer TFT immunosensor with high sensitivity and low operation voltage

An immunosensor is proposed based on the indium-gallium-zinc-oxide (IGZO) electric-double-layer thin-film transistor (EDL TFT) with a separating extended gate. The IGZO EDL TFT has a field-effect mobility of 24.5 cm2 V−1 s−1 and an operation voltage less than 1.5 V. The sensors exhibit the linear current response to label-free target immune molecule in the concentrations ranging from 1.6 to 368 × 10−15 g/ml with a detection limit of 1.6 × 10−15 g/ml (0.01 fM) under an ultralow operation voltage of 0.5 V. The IGZO TFT component demonstrates a consecutive assay stability and recyclability due to the unique structure with the separating extended gate. With the excellent electrical properties and the potential for plug-in-card-type multifunctional sensing, extended-gate-type IGZO EDL TFTs can be promising candidates for the development of a label-free biosensor for public health applications.

The electrical properties of n-ZnO/p-SnO heterojunction diodes

In the present work, n-type zinc oxide (ZnO) and p-type tin monoxide (SnO) based heterostructure diodes were fabricated on an indium-tin-oxide glass using the radio frequency magnetron sputtering technique. The prepared ZnO/SnO diodes exhibited a typical rectifying behavior, with a forward to reverse current ratio about 500 ± 5 at 2 V and turn on voltage around 1.6 V. The built-in voltage of the diode was extracted to be 0.5 V based on the capacitance-voltage (C–V) measurement. The valence and conduction band offsets were deliberated through the band energy diagram of ZnO/SnO heterojunction, as 1.08 eV and 0.41 eV, respectively. The potential barrier-dependent carrier transportation mechanism across the space charge region was also investigated.

Combined control of the cation and anion to make ZnSnON thin films for visible-light phototransistors with high responsivity

A novel oxynitride semiconductor, ZnSnON, is demonstrated. The design of this material follows the reported anion control strategy (N additives) to diminish the bandgap and the electron effective mass of ZnO on the one hand, and a cation control strategy (Sn additives) to circumvent the chemical stability problems of ZnON on the other. Comparative studies are conducted on the performance and stability of ZnSnON and ZnON films and their thin-film transistors (TFTs). It is shown that ZnSnON possesses superior transport properties and enhanced operation stability simultaneously. Such amelioration is owing to multiple factors, including the amorphous/nanocrystalline mixed phase and the bonding strength increase caused by the Sn-related oxide/oxynitride dominant in the back channel region. In addition, the Sn additives in ZnON do not alter the direct bandgap character, maintaining around 1.6 eV. The ZnSnON-TFT is photosensitive in the whole visible light region with a photoresponsivity higher than 6 × 103 A W−1. Considering the high-mobility, improved operation stability, and visible light sensing capability, this semiconductor can be used in a broad array of applications such as in active-matrix imaging arrays, interactive displays, flat X-ray detectors, etc.

High-Performance Visible-Blind Ultraviolet Photodetector Based on IGZO TFT Coupled with p–n Heterojunction

A visible-blind ultraviolet (UV) photodetector was designed based on a three-terminal electronic device of thin-film transistor (TFT) coupled with two-terminal p-n junction optoelectronic device, in hope of combining the beauties of both of the devices together. Upon the uncovered back-channel surface of amorphous indium-gallium-zinc-oxide (IGZO) TFT, we fabricated PEDOT:PSS/SnO x/IGZO heterojunction structure, through which the formation of a p-n junction and directional carrier transfer of photogenerated carriers were experimentally validated. As expected, the photoresponse characteristics of the newly designed photodetector, with a photoresponsivity of 984 A/W at a wavelength of 320 nm, a UV-visible rejection ratio up to 3.5 × 107, and a specific detectivity up to 3.3 × 1014 Jones, are not only competitive compared to the previous reports but also better than those of the pristine IGZO phototransistor. The hybrid photodetector could be operated in the off-current region with low supply voltages (<0.1 V) and ultralow power dissipation (<10 nW under illumination and ∼0.2 pW in the dark). Moreover, by applying a short positive gate pulse onto the gate, the annoying persistent photoconductivity presented in the wide band gap oxide-based devices could be suppressed conveniently, in hope of improving the response rate. With the terrific photoresponsivity along with the advantages of photodetecting pixel integration, the proposed phototransistor could be potentially used in high-performance visible-blind UV photodetector pixel arrays.