Amorphous copper tin oxide thin films are fabricated in oxygen atmosphere and at room temperature using combinatorial pulsed laser deposition approaches. Resulting thin films show n-type behavior for Cu/(Cu + Sn) < 0.5. For Cu/(Cu + Sn) > 0.7, p-type behavior is observed by qualitative Seebeck effect measurements; however, the electrical resistivity is too high for Hall effect measurements. Structural, optical, and electrical thin film properties are investigated in dependence on the cation composition and oxygen deposition pressure. An extended percolation-based random band edge model is applied to the temperature-dependent conductivity and Hall effect measurements for different deposition pressures. Extracted fit parameters are in a similar range to those reported for other amorphous oxide semiconductors. In particular, the band-disorder parameter, specifying the width of the Gaussian band edge distribution for long-range potential fluctuations, is identified as leading parameter for determining the optical and electrical properties of the thin films.

This study presents a comprehensive analysis of the microstructural, optical, and electrical transport properties of heteroepitaxial cubic spinel (111)-oriented Zn2GeO4 thin films grown on cubic spinel (111) MgAl2O4 substrates by pulsed laser deposition. The in-plane epitaxial relationships are [1-10] Zn2GeO4//[1-10] MgAl2O4 and [11-2] Zn2GeO4//[11-2] MgAl2O4, indicating a cube-on-cube epitaxy. A 316 nm thick (111) Zn2GeO4 epitaxial film has a surface root-mean-square (RMS) roughness of about 0.9 nm and a narrow rocking curve of the (444) reflex with a full width at half maximum of about 0.36 degrees. Temperature-dependent Hall effect measurements indicate that the nominally undoped films exhibit n-type semiconductor behavior. The high-quality 316 nm thick epitaxial film, with a direct optical bandgap of about 4.9 eV at room temperature, shows a notable decline in resistivity from about 60 to about 4 Omega cm, as temperature increases from 100 to 300 K. Concurrently, the Hall electron carrier mobility rises gradually from approximate to 0.5 to 5.5 cm(2) V-1 s(-1) as temperature increases from 100 to 300 K. In contrast, the Hall electron carrier concentration demonstrates minimal temperature dependence, with a value of approximate to 10(17) cm(-3). The native n-type conductivity is likely the result of unintentional dopants introduced during thin-film fabrication.

As the first discovered p-type transparent conductive material, copper(I) iodide (CuI) is considered the most competitive p-type candidate in the field of transparent electronics. Herein, we introduced a low-temperature buffer-layer-assisted strategy to grow γ-CuI with significantly improved structural quality and electrical transport properties by pulsed laser deposition. By adjusting the growth temperature, we can manipulate the rotation domain structure, control the hole concentration Nh from 1014 to 1019 cm−3, and achieve mobility μh = 25 cm2 V−1 s−1 being similar to that of bulk CuI. Based on the temperature-dependent Hall-effect measurement, the ionization energy of a shallow acceptor of EI,S = 137 ± 8 meV and that of a deeper acceptor of EI,D = 262 ± 23 meV were determined. This grown strategy not only enables high-quality CuI film preparation, but also to tailor their electrical properties for integration with n-type semiconductors in transparent electronic circuits.

Epitaxial growth of phase-pure and high-quality spinel γ-Ga2O3-based semiconductor thin films has been a big challenge for fundamental research on metastable defective inverse spinel γ-Ga2O3 semiconductors in view of potential device application. We report experimental results on epitaxial growth, microstructural, and electrical transport properties of (001)-oriented nominal γ-(Ga0.8Ge0.2)2O3 alloy semiconductor single crystal thin films with a coherent interface on cubic spinel (001) MgAl2O4 substrates by pulsed laser deposition using a Ge-rich target. Pristine films are found to be composed of about 2 nm thick insulating Ge-rich surface layers and the high-quality epitaxial n-type semiconductor film layers consisting of partially subvalent Ge2+ and Ga1+ cations as well as major components of normal Ge4+ and Ga3+ cations. Epitaxial films exhibit a direct bandgap of about 5.2 ± 0.1 eV and a valence band maximum of about 3.3 ± 0.1 eV below the Fermi level at room temperature. We further report a demonstration of γ-(Ga0.8Ge0.2)2O3 thin film-based metal-semiconductor field-effect transistor (MESFET) with the PtOx/Pt Schottky gate contact realized upon the surface pretreatment by Ar/O2 plasma etching. The MESFET device exhibits a clear field-effect with drain current modulation of about 105 orders of magnitude. This work not only significantly advances the fundamental and application-oriented research on epitaxial spinel γ-Ga2O3-based semiconductor films for practical device application but also offers new insight into microstructural characteristics of ultrawide bandgap spinel oxide semiconductor epitaxial thin films.

To tailor electrical properties of often degenerate pristine CuI, Ni is introduced as alloy constituent. Cosputtering in a reactive, but also in an inert atmosphere as well as pulsed laser deposition (PLD), is used to grow thin films. The Ni content within the alloy thin films is systematically varied for different growth techniques and growth conditions. A solubility limit is evidenced by an additional phase for Ni contents , observed in X‐Ray diffraction and atomic force microscopy by a change in surface morphology. Furthermore, metallic, nanoscaled nickel clusters, revealed by X‐Ray photoelectron spectroscopy and high‐resolution transmission electron microscopy (HRTEM), underpin a solubility limit of Ni in CuI. Although no reduction of charge carrier density is observed with increasing Ni content, a dilute magnetic behavior of the thin films is observed in vibrating sample magnetometry. Further, independent of the deposition technique, unique multilayer features are observed in HRTEM measurements for thin films of a cation composition of . Opposite to previous claims, no transition to n‐type behavior was observed, which was also confirmed by density functional theory calculations of the alloy system.

We present alpha -Ga2O3:Zr based metal-semiconductor field-effect transistors (MESFETs) with PtOx/Pt gate contacts. Pulsed laser deposition is used to grow the alpha -Ga2O3:Zr thin films in a two-step process on m-plane alpha -Al2O3. A nominally undoped alpha -Ga2O3 layer is grown at high growth temperature as growth template. Subsequently, a alpha -Ga2O3:Zr layer is grown at a lower growth temperature. We compare the performance of Ring-FET devices on a planar 30 nm thick zirconium doped layer deposited at 465 degrees C and mesa-FETs on a 35 nm thick thin film deposited at 500 degrees C. The Ring-FETs have current on/off ratios as high as 1.7 x 10 9 and a threshold voltage of - 0.28 V, and they exhibit very low mean sub-threshold swing of ( 110 +/- 20 ) mV/dec. For the mesa-FETs, smaller current on/off ratios of 4 x 10 7 are measured and a threshold voltage of - 1.5 V was obtained due to the larger thin film thickness. The on/off ratio is limited by a higher tunneling current in the off-regime. We present high voltage measurements, which show a breakdown of the mesa-FET device at - 340 V, corresponding to a high breakdown field of 1.36 MV/cm and significantly exceeding the previously achieved breakdown voltage for alpha -Ga2O3 based MESFETs.

This study presents a detailed experimental investigation of conductivity and Hall effect measurements in copper iodide (CuI), which is complemented by density-functional theory and Boltzmann-transport calculations. We have evaluated the temperature dependence of the transport data of solution-grown bulk single crystals, textured thin films grown by pulsed laser deposition, and additional data published in the literature. The density of compensating donorlike defects is determined from fits comprising ionizedimpurity scattering. This is considered for determining acceptor densities and corresponding activation energies. In the course of this investigation, meticulous attention has been paid to the intricate interplay between light-hole and heavy-hole contributions, as well as the experimental values observed in zincblende CuI. This study has yielded two distinct ionization energies for acceptors in unintentionally doped CuI, with values of EI,1 = 95 meV and EI,2 = 330 meV, respectively.

The wide band gap semiconductor κ-Ga2O3 and its aluminum and indium alloys have been proposed as promising materials for many applications. One of them is the use of inter-sub-band transitions in quantum-well (QW) systems for infrared detectors. Our simulations show that the detection wavelength range of nowadays state of the art GaAs/AlxGa1-xAs quantum-well infrared photodetectors (QWIPs) could be substantially excelled with about 1–100 μm using κ-([Al,In]xGa1-x)2O3, while at the same time being transparent to visible light and therefore insensitive to photon noise due to its wide band gap, demonstrating the application potential of this material system. Our simulations further show that the QWIPs efficiency critically depends on the QW thickness, making a precise control over the thickness during growth and a reliable thickness determination essential. We demonstrate that pulsed laser deposition yields the needed accuracy, by analyzing a series of (InxGa1-x)2O3 QWs with (AlyGa1-y)2O3 barriers with high-resolution X-ray diffraction, X-ray photoelectron spectroscopy (XPS) depth profiling, and transmission electron microscopy (TEM). While the superlattice fringes of high-resolution X-ray diffraction only yield an average combined thickness of the QWs and the barrier and X-ray spectroscopy depth profiling requires elaborated modeling of the XPS signal to accurately determine the thickness of such QWs, TEM is the method of choice when it comes to the determination of QW thicknesses.

Anion doping is an efficient method for modifying the electrical property of the p‐type semiconductor CuI. However, adjustment of the hole density is still challenging. Using sputtering and spin coating techniques, well‐controlled S‐doping of CuI thin films has been realized. The spin‐coated samples present a single (111) out‐of‐plane orientation and very high crystallinity, which is comparable with previously reported epitaxial CuI thin films. The sputtered thin films have advantages in surface morphology and conductivity. Substituting S for I can achieve efficient acceptor doping of CuI for both the physical and chemical growth methods. The highest conductivity of CuI appears at 2.0 at% of S doping, and the doping efficiency is influenced by the self‐compensation effect.

Structural and electrical properties of undoped and doped α‐Ga2O3 thin films grown by pulsed laser deposition on m‐plane sapphire in a two‐step process are presented. A buffer layer of undoped α‐Ga2O3 is introduced below the electrically active thin film to improve the crystal quality and enable the stabilization of the α‐phase at lower substrate temperatures for sufficient dopant incorporation. Donor doping of the active layers with tin, germanium, and silicon, respectively, is realized below a critical substrate temperature of 600 °C. Depth‐resolved X‐ray photoelectron spectroscopy measurements on tin‐doped samples reveal a lower amount of tin in the bulk thin film compared to the surface and a lower tin incorporation for higher substrate temperatures, indicating desorption or float‐up processes that determine the dopant incorporation. Electron mobilities as high as 17 cm2 V−1 s−1 (at ) and 37 cm2 V−1 s−1 (at ) are achieved for tin‐ and germanium doping, respectively. Further, a narrow window of suitable annealing temperature from 680 to 700 K for obtaining ohmic Ti/Al/Au layer stacks is identified. For higher annealing temperatures, a deterioration of the electrical properties of the thin films is observed suggesting the need for developing low temperature contacting procedures for α‐Ga2O3‐based devices.

Metal-semiconductor field-effect transistor (MESFET) devices based on pulsed laser deposition (PLD) grown In2O3 thin films with on-off ratios exceeding 6 orders of magnitude and low sub-threshold swing values close to the thermodynamic limit are reported. Oxygen plasma treatment and compensation doping with Mg are utilized to suppress the accumulation of electrons at the surface of In2O3, which is a major obstacle for its use as an active material in electronic devices. The influence of both methods is investigated on the electrical properties of thin films as determined by Hall effect measurements on samples of varying film thickness. Using the performance of vertical Schottky barrier diodes as a benchmark, fundamental plasma parameters such as input power and background gas pressure are optimized.

Schottky barrier diodes on α−Ga2O3:Sn heteroepitaxial thin films grown by pulsed laser deposition on m-plane sapphire substrates are reported. Sets of co-planar diodes were fabricated with different metals and different deposition methods. The current rectification and effective Schottky barrier height of oxidized contacts realized by reactive sputtering significantly exceed the values of non-oxidized contacts realized by thermal evaporation or sputtering in an inert argon atmosphere. The best values obtained are rectification of about eight orders of magnitude (±2 V) and 1.3 eV effective barrier height. The current-voltage characteristics of selected non-oxidized and oxidized platinum diodes have been studied as a function of measurement temperature. The temperature dependence of the effective barrier height and the ideality factor of the diodes were fitted taking into account the lateral potential fluctuations of the barrier potential. The determined mean barrier heights and standard deviations are in the range of 1.76–2.53 and 0.2–0.33 eV, respectively, and are classified with respect to the literature and fulfill a well-established empirical correlation (Lajn’s rule) for a variety of Schottky barrier diodes on different semiconducting materials.

Structural, morphological, and optical properties of (In1-xGax)(2)O-3 thin films are reported as a function of the cation composition. A material library with 0.1 <= x <= 0.64 was fabricated by discrete combinatorial synthesis on r-plane sapphire substrates using pulsed laser deposition. The samples crystallize in the cubic bixbyite phase for x <= 0.35. The lattice constant and absorption edge energy systematically decrease and increase, respectively, with increasing Ga content up to x = 0.2. For higher Ga admixtures, both saturate. In addition, a significant change in surface morphology occurs at x similar to 0.2. Transmission electron microscopy examinations of selected samples show a homogeneous incorporation of Ga2O3 into cubic In2O3 for x = 0.11, while a segregation of Ga-rich and In-rich regions can be seen for x = 0.22 and x = 0.35. In the sample with x = 0.35, the Ga-rich regions exhibit a preferred orientation with an angle of 45 degrees-55 degrees with respect to the substrate normal, which has been shown to result from a correspondingly faceted In-rich bixbyite layer at the substrate-thin film interface.

Amorphous transparent conductors (a-TCs) are key materials for flexible and transparent electronics but still suffer from poor p-type conductivity. By developing an amorphous Cu(S,I) material system, record high hole conductivities of 103-104 S cm-1 have been achieved in p-type a-TCs. These high conductivities are comparable with commercial n-type TCs made of indium tin oxide and are 100 times greater than any previously reported p-type a-TCs. Responsible for the high hole conduction is the overlap of large p-orbitals of I- and S2- anions, which provide a hole transport pathway insensitive to structural disorder. In addition, the bandgap of amorphous Cu(S,I) can be modulated from 2.6 to 2.9 eV by increasing the iodine content. These unique properties demonstrate that the Cu(S,I) system holds great potential as a promising p-type amorphous transparent electrode material for optoelectronics.

We introduce a novel technique, masked-assisted radial-segmented target pulsed-laser deposition (MARS-PLD) for unprecedented capabilities in area-selective physical vapor deposition. The MARS-PLD setup consists of a conventional PLD chamber with mechanical feedthrough for a laterally movable mask or mask set. By this means and, in principle, the arbitrary choice of a shadow mask layout, any desired area on a substrate can be masked in order to create multinary lateral and vertical material composition gradients using radially segmented targets already described in the literature [Kneiß et al., ACS Comb. Sci. 20, 643–652 (2018)]. To illustrate the capabilities of this method, we fabricated material gradients in (Mg,Zn)O thin films with a nearly linear spatial variation of the cation composition of 15at.%mm−1. Additionally, we fine-tuned our setup to fabricate a material gradient on a predefined two-dimensional lateral pattern to demonstrate the versatile capabilities of the MARS-PLD technique.

We investigate α-(AlxGa1-x)2O3 layers deposited by PLD for 0≤x≤1 on a- and m-plane sapphire. RSM measurements reveal a fundamental difference for these planes. Pseudomorphic α-(AlxGa1-x)2O3 on m-plane sapphire shows a shear strain e'5 along the c-axis vanishing on a-plane sapphire. Similarly, only relaxed m-plane α-(AlxGa1-x)2O3 exhibits a global lattice tilt in c-axis direction. Modeling of lattice constants and e'5 as function of x prove the shear strain to be due to the non-vanishing C14 component of the stress-strain tensor for α-(AlxGa1-x)2O3 contributing only for the m-plane. We further explain the occurrence of the lattice tilt and identify possible relaxation mechanisms.

We have fabricated a novel type of ultracompact spectrometer without dispersive element(s) suitable for the use in smartphones. It comprises a waveguide with a linear photodetector array on top. The photosensitive layer features a steep chemical concentration gradient, fabricated from (MgxZn1-x)O, allowing for spectral detection in the UV. The dimensions of the device make it ultracompact with a volume of less than 1 cubic millimeter.

We present κ-Ga2O3 layers grown by tin-assisted PLD on highly conductive Al-doped ZnO back contact layers. κ-Ga2O3 deposited on c-sapphire typically exhibits no lateral current flow. Significant currents can only be detected when a vertical current flow through the κ-Ga2O3 layer is enabled by the back contact confirming a strong conductivity anisotropy possibly due to suppressed transport across rotational domain boundaries. Pt/PtOx or Pd/PdOx Schottky contacts and NiO or ZnCo2O4 p-type contacts exhibit rectification ratios up to seven orders of magnitude. Further, we obtain a mean barrier height of ~2.1 eV and ideality factors as low as ~1.3 for Pt/PtOx/κ-Ga2O3 Schottky barrier diodes.

We investigate the electrical transport in amorphous oxide semiconductors by applying the percolationbased random band-edge model proposed by Nenashev et al. [Phys. Rev. B 100, 125202 (2019)] to multicationic, multianionic, and multinary materials. We modify the model by introducing the Hallscattering factor. This allows us to evaluate, besides the conductivity, the temperature-dependent free charge-carrier concentration and Hall mobility, additionally enabling the inclusion of localized tail states in the model. The extended model allows analysis of pulsed-laser deposited amorphous zinc tin oxide, magnetron-sputtered amorphous zinc oxynitride, and zinc magnesium oxynitride thin films with carrier concentrations ranging from 10(16) to 10(19) cm(-3) at room temperature. Excellent agreement of the extended model data with the measured electrical properties is found for the investigated temperature regime of 50 to 300 K. In addition, we extract critical parameters of the random band-edge model and discuss them with regard to varying deposition parameters and different anion and cation concentrations. In particular, we find the standard deviation of the mobility edge distribution to be ranging between 20 and 60 meV for the investigated materials.