Electrically switchable bistable conductance that occurs in ferroelectric materials has attracted growing interest due to its promising applications in data storage and in‐memory computing. Sc‐alloyed III‐nitrides have emerged as a new class of ferroelectrics, which not only enable seamless integration with III‐nitride technology but also provide an alternative solution for CMOS back end of line integration. In this paper, the resistive switching behavior and memory effect in an ultrawide‐bandgap, high Curie temperature, fully epitaxial ferroelectric ScAlN/GaN heterostructure is reported for the first time. The structure exhibits robust ON and OFF states that last for months at room temperature with rectifying ratios of 60–210, and further shows stable operation at high temperatures (≈670 K) that are close to or even above the Curie temperature of most conventional ferroelectrics. Detailed studies suggest that the underlying mechanism is directly related to a ferroelectric field effect induced charge reconstruction at the hetero‐interface. The robust resistive switching landscape and the electrical polarization engineering capability in the polar heterostructure, together with the promise to integrate with both silicon and GaN technologies, can pave the way for next‐generation memristors and further enable a broad range of multifunctional and cross‐field applications.

ScAlN is an emerging ultrawide bandgap semiconductor for next-generation radio frequency electronic devices. Here, we show that the material quality of ScAlN grown by molecular beam epitaxy can be drastically improved by alloying with Ga. The resulting quaternary alloy ScAlGaN exhibits a single-phase wurtzite structure, atomically smooth surface, high crystal quality, sharp interface, and low impurity concentration. Most significantly, oxygen impurity incorporation in ScAlGaN is found to be three to four orders of magnitude lower compared to that for ScAlN grown on AlN templates utilizing a similar Sc source. We further demonstrate that ScAlGaN/GaN superlattices exhibit clear periodicity with sharp interfaces. Moreover, GaN high electron mobility transistors with high sheet electron density and high mobility have been realized using ScAlGaN as a barrier. This work provides a viable approach for achieving high-quality Sc-III-N semiconductors that were not previously possible and further offers additional dimensions for bandgap, polarization, interface, strain, and quantum engineering.

architectures employing analogue inmemory computing techniques are being intensively investigated in pursuit of reducing energy consumption and latency. [1][2][3][4] Two-terminal memristors, owing to their dense device structure, ability to store and process data at the same location, simple weight update scheme, and straightforward vector-matrix multiplication (VMM) in a crossbar array fashion, have been widely explored for neuromorphic computing, machine learning, and edge computing applications. [5,6] To this end, various non-volatile memories (NVMs), including resistive memory, flash memory, phase-change memory, and magneto-resistive memory have been explored to carry out feature extraction, image processing, and neuro-inspired computing. [6][7][8][9][10][11][12][13][14] Ferroelectric resistive memory utilizes multi-domain polarization switching dynamics in a ferroelectric material, which has been shown to deliver fast potentiation and depression programming, symmetric and linear conductance response, and large ON/OFF conductance ratios. [15][16][17][18][19] To harness the well-established periphery circuitry and increase integration density, however, it is desired to integrate ferroelectric memory arrays with mainstream semiconductor technology, which significantly narrows down the materials available. [20][21][22] The discovery of ferroelectricity in HfO 2 -based materials has rejuvenated the interest in ferroelectric memory with both front-end-of-line and back-endof-line compatibility. To date, however, related two terminal resistive memories still suffer from low ON/OFF ratios, wakeup effect and significant imprint oscillations and retention loss. [19,21,[23][24][25][26][27] Although recent studies have shown that HfO 2based field effect transistors are much less affected by above limitations, [28] two-terminal memristors offer the advantages of significantly reduced device area and operation power and, therefore, have remained a subject of intensive study.Those issues can potentially be addressed by exploiting a new class of ferroelectrics -nitride ferroelectrics. [29] Sc-alloyed III-nitrides, i.e., ScAlN and ScGaN, have been discovered with giant remnant polarization and superior thermal stability. [29][30][31][32][33] The wide processing temperature window and the approximation of the lattice with other nitride materials promise good compatibility and seamless integration with both GaN and silicon technology. [34][35][36][37][38] In addition, the wake-up effect and Computing in the analog regime using nonlinear ferroelectric resistive memory arrays can potentially alleviate the energy constraints and complexity/footprint challenges imposed by digital von Neumann systems. Yet the current ferroelectric resistive memories suffer from either low ON/OFF ratios/imprint or limited compatibility with mainstream semiconductors. Here, for the first time, ferroelectric and analog resistive switching in an epitaxial nitride heterojunction comprising ultrathin (≈5 nm) nitride ferroelectrics, i.e., ScAlN, with poten...

We report on the thickness scaling behavior of ferroelectric Sc0.3Al0.7N (ScAlN) films grown on Mo substrates by molecular beam epitaxy. Switchable ferroelectricity is confirmed in ScAlN films with thicknesses ranging from 100 to 5 nm. An increase in coercive field and a significant diminution of remnant polarization are found when the ferroelectric layer is scaled down to below 20 nm. Notably, a switching voltage of 2–3.8 V and saturated remnant polarization of ∼23 μC/cm2 are measured in 5 nm thick ScAlN. X-ray diffractions and transmission electron microscopy studies indicate that the increase in coercive field and diminishment in switchable polarization can be closely linked to the surface oxidation and strain state in ultrathin ScAlN films. This work sheds light on the fundamental thickness scaling fingerprints of ScAlN thin films and represents an important step for next-generation compact and power-efficient devices and applications based on nitride ferroelectrics.

We report on the effect of dislocation density on the ferroelectric properties of single-crystalline ScAlN thin films grown by molecular beam epitaxy. Wurtzite phase and atomically smooth ScAlN films have been grown on bulk GaN, GaN on sapphire, and GaN on Si substrates with dislocation densities ranging from ∼107 to 1010 cm−2. Despite the significant difference in dislocation density, ferroelectricity is observed in all three samples. The presence of high densities of dislocations, however, results in enhanced asymmetric P–E loops and overestimated remnant polarization values. Further measurements show that the leakage current and breakdown strength can be improved with decreasing dislocation density. Detailed studies suggest that trapping/detrapping assisted transport is the main leakage mechanism in epitaxial ferroelectric ScAlN films. This work sheds light on the essential material quality considerations for tuning the ferroelectric property of ScAlN toward integration with mainstream semiconductor platforms, e.g., Si, and paves the way for next-generation electronics, optoelectronics, and piezoelectronics.