Recent Developments in p‐Type Oxide Semiconductor Materials and Devices

Abstract

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.

Complementary Integrated Circuits Based on p-Type SnO and n-Type IGZO Thin-Film Transistors

“…From the point of industrial application, high gain of complementary inverter is quite desirable in order to achieve large noise margins of the integrated circuits. However, to the best of our knowledge, the gains of the reported complementary inverters based on n-and p-type oxides are not higher than 30 under a supply voltage of 10 V until now [2,3,12,13,15,16,18,24] high-performance n-type IGZO TFTs and p-type SnO TFTs via room-temperature sputtering method which is suitable for large-scale fabrication and commercialization for transparent/flexible electronics. Moreover, we realized the integration of SnO and IGZO TFTs to achieve complementary inverters with extremely high voltage gain up to 112.…”

“…XIDE semiconductors have received much attention due to a number of advantages including low cost, low fabrication temperatures, high carrier mobilities, good transparency in visible region, mechanical flexibility, as well as scalable deposition methods compared with amorphous silicon [1][2][3][4]. Under the advantages mentioned above, oxide semiconductors have been regarded as one of the most promising candidates for transparent/flexible electronics [2,3].…”

“…Under the advantages mentioned above, oxide semiconductors have been regarded as one of the most promising candidates for transparent/flexible electronics [2,3].…”

“…Subthreshold Schottky-barrier IGZO TFTs have been demonstrated to be useful for sensor interface circuits in wearable electronics [6]. On the another hand, p-type oxide semiconductors are far behind mainly because of low on/off ratio, low hole mobility, and high subgap trap density [3]. However, p-type TFTs are essential in order to fabricate complementary integrated circuits with low static power consumption, high noise margin, high yield, and high reliability for actual applications.…”

“…Realizing sophisticated all-oxide circuits operating in complementary mode has been challenging due to the difficulty in making high-performance p-type oxide TFTs matched with their n-type counterparts. Up to date, SnO is considered as the most promising p-type oxide due to its high field-effect hole mobility, good uniformity for large-scale fabrication, and high stability in ambient air [3,7]. To realize complementary inverters, one can either combine an n-type TFT and a p-type TFT or use two ambipolar TFTs.…”