A pn-heterojunction is fabricated by depositing an n-type β-Ga2O3 film by pulsed laser deposition (PLD) on c-cut Al2O3. P-type cuprous oxide films, Cu2O, are then deposited by PLD, as well as by radio frequency (RF) magnetron sputtering. It is concluded that hole injection is prohibited by a 3.26 eV valence band barrier, as measured by X-ray photo-electron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Heterojunction diode structures are prepared on the front side and electrical measurements demonstrate a rectification ration of 8 orders of magnitude and an ideality factor close to 2, indicating interface recombination-controlled forward current. The junction is also optically active and shows a very fast photo-response to 275 nm UV light. 

MXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors (MSCs). Despite its superior electrochemical performance, only a few studies have reported MXene-based ultrahigh-rate (>1000 mV s−1) on-paper MSCs, mainly due to the reduced electrical conductance of MXene films deposited on paper. Herein, ultrahigh-rate metal-free on-paper MSCs based on heterogeneous MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)-stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser scribing. With a footprint area of only 20 mm2, the on-paper MSCs exhibit excellent high-rate capacitive behavior with an areal capacitance of 5.7 mF cm−2 and long cycle life (>95% capacitance retention after 10,000 cycles) at a high scan rate of 1000 mV s−1, outperforming most of the present on-paper MSCs. Furthermore, the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal-free on-paper MSC arrays, which can also be simultaneously charged/discharged at 1000 mV s−1, showing scalable capacitive performance. The heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on-paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics. 

The underlying mechanism behind the metal-to-insulator transition in VO2 is still a topic of intense debate. The two leading theoretical interpretations associate the transition with either electron-lattice or electron-electron correlations. Novel experimental results are required to converge towards one of the two scenarios. Here we report on a temperature-dependent angle-resolved photoelectron study of VO2 thin films across the metal-to-insulator transition. The obtained experimental results are compared to density functional theory calculations. We find an overall energy shift and compression of the electronic band structure across the transition while the overall band topology is conserved. The results demonstrate the importance of electron-electron correlations in establishing the insulating state.

Pulsed laser ablation is used to form high-quality silicon-doped β-Ga2O3 films on sapphire by alternatively depositing Ga2O3 and Si from two separate sources. X-ray analysis reveals a single crystallinity with a full width at half maximum for the rocking curve around the (−201) reflection peak of 1.6°. Silicon doping concentration is determined by elastic recoil detection analysis (ERDA), and the best electrical performance is reached at a Si concentration of about 1 × 1020 cm−3, using optimized deposition parameters. It is found that a high crystalline quality and a mobility of about 2.9 cm2 (V s)−1 can be achieved by depositing Si and Ga2O3 from two separate sources. Two types of Schottky contacts are fabricated: one with a pure Pt and one with a PtOx composition. Electrical results from these structures are also presented. 

We report on optical dispersion and temperature dependence of latching-type magneto-optical properties of heavily Ga-doped bismuth iron garnet films rf-magnetron sputtered onto Gd3Ga5O12 (001) and (111) substrates. At lambda = 677 nm and room temperature, epitaxial Bi3Fe3.34Ga1.66O12 (001) and (111) films show, respectively, saturation Faraday rotation theta(Fsat) = - 0.92 x 10(4) and - 1.05 x 10(4) deg/cm, transmittance T = 0.86 and 0.81, magnetic hysteresis theta(F)-H loop squareness theta(Frem)/theta(Fsat) = 0.84 and 1.0, and coercive field H-c = 6.76 and 24.03 kA/m. Film's Faraday rotation is nicely fitted by molecular field Neel theory in the whole temperature range from T-C = 316 K down to 85 K where theta(Fsat) = - 1.9 x 10(4) deg/cm and H-c = 151.20 kA/m.

We report the properties of 1D all-garnet heteroepitaxial 21 layered magneto-optical photonic crystal designed and fabricated for the resonance wavelength 750 +/- 3 nm. It is composed of alternating magnetooptical-active Bi3Fe5O12 and transparent Sm3Ga5O12 quarter-wavelength layers radio frequency magnetron sputtered onto single crystalline Ca, Mg, Zr:Gd3Ga5O12(111) substrate. Edges of the band gap and resonant central peaks in transmission and Faraday rotation spectra experience significant (about 60 nm) "blueshift" when the angle of light incidence increases up to 70 degrees. Lower reflectance and strong enhancement of Faraday rotation of TE mode compared to the TM-polarized light testify a waveguiding of TE-mode within a resonant lambda/2 Bi3Fe5O12 cavity.

4H-SiC electronics can operate at high temperature (HT), e.g., 300A degrees C to 500A degrees C, for extended times. Systems using sensors and amplifiers that operate at HT would benefit from microcontrollers which can also operate at HT. Microcontrollers require nonvolatile memory (NVM) for computer programs. In this work, we demonstrate the possibility of integrating ferroelectric vanadium-doped bismuth titanate (BiTV) thin films on 4H-SiC for HT memory applications, with BiTV ferroelectric capacitors providing memory functionality. Film deposition was achieved by laser ablation on Pt (111)/TiO2/4H-SiC substrates, with magnetron-sputtered Pt used as bottom electrode and thermally evaporated Au as upper contacts. Film characterization by x-ray diffraction analysis revealed predominately (117) orientation. P-E hysteresis loops measured at room temperature showed maximum 2P (r) of 48 mu C/cm(2), large enough for wide read margins. P-E loops were measurable up to 450A degrees C, with losses limiting measurements above 450A degrees C. The phase-transition temperature was determined to be about 660A degrees C from the discontinuity in dielectric permittivity, close to what is achieved for ceramics. These BiTV ferroelectric capacitors demonstrate potential for use in HT NVM applications for SiC digital electronics.

The formation of interfacial oxides during heat treatment of dielectric films on 4H-SiC has been studied. The 4H-SiC surface has been carefully prepared to create a clean and abrupt interface to Al2O3. An amorphous, 3 nm thick, Al2O3 film has been prepared on 4H-SiC by atomic layer deposition and rapid thermal annealing was then performed in N2O ambient at 700 degrees C and 1100 degrees C during 1 min. The samples were studied by time-of-flight medium energy ion scattering (ToF-MEIS), with sub-nanometer depth resolution and it is seen that, at both annealing temperatures, a thin SiOx (1 <= x <= 2) is formed at the interface. Our results further indicate that carbon remains in the silicon oxide in samples annealed at 700 degrees C. Additional electrical capacitance voltage measurements indicate that a large concentration of interface traps is formed at this temperature. After 1100 degrees C annealing, both MEIS and XRD measurements show that these features disappear, in accordance with electrical data.

We demonstrate the control of Gilbert damping in 65-nm-thick yttrium iron garnet (YIG) films using a spin-polarized current generated by a direct current through a nanocontact, spin filtered by a thin Co layer. The magnetodynamics of both the YIG and the Co layers can be excited by a pulse-modulated microwave current injected through the nanocontact and the response detected as a lock-in amplified voltage over the device. The spectra show three clear peaks, two associated with the ferromagnetic resonance (FMR) in each layer, and an additional Co mode with a higher wave vector proportional to the inverse of the nanocontact diameter. By varying the sign and magnitude of the direct nanocontact current, we can either increase or decrease the linewidth of the YIG FMR peak consistent with additional positive or negative damping being exerted by the nonlocal spin current injected into the YIG film. Our nanocontact approach thus offers an alternative route in the search for auto-oscillations in YIG films.