The development of transparent p-type oxide semiconductors with good performance could be a true enabler for a variety of applications, where transparency, power efficiency and more circuit complexity are needed. Such applications include transparent electronics, displays, sensors, photovoltaics, memristors, and electrochromics. Hence, we review recent developments in materials and devices based on p-type oxide semiconductors, including ternary Cu-bearing oxides, binary copper oxides, tin monoxide, spinel oxides and nickel oxides. The crystal and electronic structures of these materials are reviewed, along with approaches to enhance valence band dispersion to reduce effective mass and increase mobility.Strategies to reduce the interfacial defects, off state current, and material instability are discussed. Furthermore, we show that promising progress has been made in the performance of various type of devices based on p-type oxides. For example, transparent oxide-based p-n junction diodes have experienced significantly improved performance, where rectification ratios >10 7 have been achieved. The performances of thin-film transistors and inverters have also been modestly improved. For example, thin-film transistors with field-effect mobilities exceeding 5 cm 2 V -1 s -1 have been reported. In addition, several innovative approaches were developed to fabricate transparent complementary metal oxide semiconductor (CMOS) 2 devices. These approaches include novel device fabrication schemes and utilization of surface chemistry effects, resulting in good inverter gains (as high as 120 has been demonstrated).Some progress has also been made in reducing the interfacial defects and off state currents using capping layers, high quality dielectrics and surface treatments. Resistive memory devices and hole transport layer in optoelectronic devices, mostly based on nickel oxide, have made decent progress. Transparent ferroelectric memory devices comprising p-type oxides have also been reported recently showing good hole mobilities (~3.3 cm 2 V -1 s -1 ) and good retention characteristics. This even includes multistate memory devices that show good stability. Nanoscale (e.g. nanowire) devices have now been reported using p-type oxides and do show performance improvements at scaled device geometry. New process developments have been reported, and some p-type oxides can now be deposited using atomic layer deposition and chemical routes, with promising performances. However, despite these recent developments, p-type oxides still lag in performance behind the n-type counterparts, which have entered volume production in the display market. The recent successes along with the hurdles that stand in the way of commercial success of p-type oxide semiconductors are presented in this review.

Here, we report the fabrication of nanoscale (15 nm) fully transparent p-type SnO thin film transistors (TFT) at temperatures as low as 180 °C with record device performance. Specifically, by carefully controlling the process conditions, we have developed SnO thin films with a Hall mobility of 18.71 cm(2) V(-1) s(-1) and fabricated TFT devices with a linear field-effect mobility of 6.75 cm(2) V(-1) s(-1) and 5.87 cm(2) V(-1) s(-1) on transparent rigid and translucent flexible substrates, respectively. These values of mobility are the highest reported to date for any p-type oxide processed at this low temperature. We further demonstrate that this high mobility is realized by careful phase engineering. Specifically, we show that phase-pure SnO is not necessarily the highest mobility phase; instead, well-controlled amounts of residual metallic tin are shown to substantially increase the hole mobility. A detailed phase stability map for physical vapor deposition of nanoscale SnO is constructed for the first time for this p-type oxide.

obtained when graphene is patterned into porous 3D network structure, due to its large specifi c surface area and a highly conductive pathways stimulating adequate effi ciency in charge transfer and mass transport. [ 3b,4 ] Though these layouts offer excellent functionality, the devices fabricated from these materials are commonly realized by standard microfabrication involving spin/spray-coating or sometimes screen printing techniques that are either expensive or require additional binders or additives, which can be detrimental for electrochemical sensing applications. [ 3a,5 ] In spite of this, the complex solution processing of graphene derived materials leads aggregation and re-stacking between individual graphene sheets as a result of the strong sheet-tosheet van der Waals interactions, greatly compromising the intrinsic high specifi c surface area and hence lessening the electrochemical activity. [ 5b,6 ] These issues limit their integration with functional on-chip device applications. Hence, it is highly challenging to fabricate the graphitic carbon materials with desired surface functionality, having 3D architecture enriched with edge planes, while avoiding complex solution processing and additive/binder-free approach.Computer aided laser scribing technique to produce reduced graphene oxide pattern from solution processed graphite oxide (GO) opened up a new direction in direct on-chip fabrication of micropower units by Kaner group. [ 7 ] However, this technique still requires multi-step chemical processing before patterning. Here, we adopt a direct writing process to fabricate patterns of graphitic carbon on commercial fl exible polyimide (PI) surface employing a laser scribing approach, a process that has been reported by the Tour group for fabricating 3D microsupercapacitor. [ 8 ] Interestingly, the proposed process offers a binderfree, porous, conductive carbon with 3D interconnected network, rich in defects and edge plane sites, but still functional enough to be wetted by the aqueous electrolytes, making it a potential electrode material for electrochemical sensing applications. Also, this self-supporting architecture offers large specifi c surface area, which can facilitate the electrolyte accessibility to the electrode surfaces and hence is favorable for electrochemical sensing. In addition, direct writing of the electrochemical sensors can enable integration of these sensors with other electronic and energy storage elements (e.g., microsupercapacitors, thin-fi lm batteries, and printed electronics). The above This study reports the fabrication of fl exible electrochemical sensors using a direct-write laser scribing process that transforms commercial polyimide sheet into graphitic carbon with self-standing porous 3D morphology, and abundant edge planes. The heterogeneous electron transfer rate ( k 0 ) of the laser scribed graphene (LSG) electrodes for both inner-sphere and outer-sphere redox mediators, ferrocyanide ([Fe(CN) 6 ] 4− ) and hexaammineruthenium ([Ru(NH 3 ) 6 ] 3+ ) are estimated to ...

A biosensor platform based on Au/MXene nanocomposite for sensitive enzymatic glucose detection is reported. The biosensor leverages the unique electrocatalytic properties and synergistic effects between Au nanoparticles and MXene sheets. An amperometric glucose biosensor is fabricated by the immobilization of glucose oxidase (GOx) enzyme on Nafion solubilized Au/ MXene nanocomposite over glassy carbon electrode (GCE). The biomediated Au nanoparticles play a significant role in facilitating the electron exchange between the electroactive center of GOx and the electrode. The GOx/Au/MXene/Nafion/GCE biosensor electrode displayed a linear amperometric response in the glucose concentration range from 0.1 to 18 mM with a relatively high sensitivity of 4.2 μAmM−1 cm−2 and a detection limit of 5.9 μM (S/N = 3). Furthermore, the biosensor exhibited excellent stability, reproducibility and repeatability. Therefore, the Au/MXene nanocomposite reported in this work is a potential candidate as an electrochemical transducer in electrochemical biosensors.

Graphene as a transducer material has produced some of the best-performing sensing approaches to date opening the door toward integrated miniaturized all-carbon point-of-care devices. Addressing this opportunity, laser-scribed graphene (LSG) electrodes are demonstrated here as highly sensitive and reliable biosensor transducers in blood serum analysis. These flexible electrodes with large electrochemical surface areas were fabricated using a direct-write laser process on polyimide foils. A universal immobilization approach is established by anchoring 1-pyrenebutyric acid to the graphene and subsequently covalently attaching an aptamer against the coagulation factor thrombin as an exemplary bioreceptor to the carboxyl groups. The resulting biosensor displays extremely low detection limits of 1 pM in buffer and 5 pM in the complex matrix of serum.