We report pulsed laser deposition being a quite suitable growth method for smooth and transparent p-type copper iodide (CuI) thin films with tailored electrical properties. The film characteristics are strongly influenced by the temperature during growth. Increasing substrate temperatures result in significant improvements in crystallinity compared to deposition at room temperature. In contrast to other growth techniques, the hole carrier density p can be varied systematically between 5 × 1016 cm−3 and 1 × 1019 cm−3 with hole mobilities up to 20 cm2/V s for lowest p. The surfaces exhibit irregularly shaped grains, and the roughness can be decreased down to 1 nm. Furthermore, the samples exhibit high transmittance up to 90% in the visible spectrum.

The structural, surface, and optical properties of phase-pure κ-(AlxGa1−x)2O3 thin films on c-sapphire and STO(111):Nb substrates as well as on MgO(111) and κ-Ga2O3 templates are reported as a function of alloy composition for x < 0.4. The thin films were grown by tin-assisted pulsed laser deposition (PLD). For the variation of the Al-content, we utilized radially segmented PLD targets that enable the deposition of a thin film material library by discrete composition screening. Growth on κ-Ga2O3 (001) thin film templates enhanced the phase pure growth window remarkably up to x = 0.65. The crystallization of the κ-phase was verified by X-ray diffraction 2θ-ω-scans for all samples. Both in- and out-of-plane lattice constants in dependence on the Al-content follow a linear relationship according to Vegard’s law over the complete composition range. Atomic force microscope measurements confirm smooth surfaces (Rq ≈ 1.4 nm) for all investigated Al-contents. Furthermore, bandgap tuning from 4.9 eV to 5.8 eV is demonstrated and a linear increase in the bandgap with increasing Al-content was observed.

Combinatorial material synthesis has led to a significant acceleration in the optimization of multinary compounds and a more efficient usage of source and substrate materials. Various growth methods, including physical vapor deposition, can be adopted to realize material libraries. Herein, two approaches to combinatorial material synthesis based on ablation of segmented targets during pulsed‐laser deposition are reviewed. For these two processes, either laterally or radially segmented targets are utilized and allow the creation of lateral and vertical composition spreads, respectively. Radially segmented targets can additionally be used to synthesize a discrete binary material library. Both approaches are introduced by calculating the expected material distribution with a simple geometric plasma expansion model. Then, experimentally determined elemental distributions and growth rates are compared to predictions and it is demonstrated that differences between calculated and experimental data contain vital information on the influence of, for example, thermodynamic processes on the growth mechanism.

Structural properties of rhombohedral α‐(AlxGa1−x)2O3 thin films grown by two combinatorial pulsed laser deposition (PLD) techniques are investigated for the entire composition range. One α‐(AlxGa1−x)2O3 thin film is deposited on a 2 inch in diameter large a‐plane sapphire substrate using the continuous composition spread (CCS) PLD technique to fabricate a thin film with varying Al content ranging between x = 0.13 and x = 0.84. Laterally homogeneous α‐(AlxGa1−x)2O3 thin films exhibiting discrete Al contents are fabricated using radially segmented PLD targets on (11.0) Al2O3. Independent of the PLD technique, for x ≈ 0.55, a change from relaxed to pseudomorphic growth is observed as confirmed by the evolution of in‐ and out‐of‐plane lattice constants. The crystal structure is studied depending on the cation composition by X‐ray diffraction confirming the fabrication of epitaxial, corundum‐structured thin films.

For every semiconducting material, the long-term stability of thin film characteristics is a crucial necessity for device applications. This is particularly true for the p-type semiconductor CuI, where the thin film properties are especially sensitive to environmental influences and motivate the application of capping materials. Utilizing pulsed laser deposition (PLD) and Al2O3 cappings, we performed systematic studies on the N2/O2 partial pressure during growth and the effect of layer thickness. Our results suggest that oxygen, acting as an acceptor, and its diffusion through Al2O3 and CuI dominate the conductivity of PLD grown CuI thin films. The diffusion process of atmospheric oxygen into CuI was traced with 18O-isotopes. Additionally, the transparency and morphology of CuI films are also affected by the oxygen supply during capping growth. These results challenge the currently accepted idea that intrinsic, and not extrinsic, effects determine the conductivity of CuI thin films.

The impact of the intentional selenium doping of CuI thin films is investigated concerning crucial crystalline, electrical and optical properties. For selenium contents in between 0.1 at.% and 1 at.%, the carrier density can be systematically adjusted by the selenium supply during growth between cm and cm while transparency and crystallinity remain unaffected. By temperature‐dependent Hall‐effect measurements, a carrier freeze out is observed and the binding energy of the selenium dopant is determined. The long‐term electrical stability in combination with cappings is significantly improved compared to undoped or oxygen doped CuI. However, for selenium contents exceeding 1 at.%, major crystalline changes are observed that are presumably correlated to a phase transformation. Transmission and electrical measurements suggest that the solubility limit of Se in CuI is about 1 at.% since a degradation of the transparency and decreasing free hole densities are observed for Se contents exceeding 1 at.%. Hence, the doping limit for Se in CuI corresponds to 1 at.%.

Vertical composition gradients of ternary alloy thin films find applications in numerous device structures. Up to now such gradients along the growth direction have not been realized by standard pulsed laser deposition (PLD) systems. In this study, we propose an approach based on a single elliptically segmented PLD target suited for the epitaxial growth of vertically graded layers. The composition of the thin films can be varied by a simple adjustment of the position of the PLD laser spot on the target surface. We demonstrate this principle for the Mg x Zn1–x O alloy system. Such vertically composition-graded Mg x Zn1–x O thin films exhibit high optical quality and a well-defined Mg-content for each layer. No signs of interdiffusion of Mg-atoms between the layers have been found. Further, this method is capable to deposit homogeneous thin films with any desired, well-defined cation composition having the same high optical and structural quality as films grown by conventional PLD.

High quality heteroepitaxial (001)-oriented κ-(AlxGa1−x)2O3/κ-Ga2O3 quantum well superlattice heterostructures were deposited by tin-assisted pulsed laser deposition on c-sapphire substrates. Sharp superlattice fringes up to the ninth order in XRD patterns for Al-contents up to about 50 at. % confirm excellent structural quality and smooth interfaces in the multilayers on par with reports on homoepitaxial superlattices in the monoclinic modification. By employing elliptically segmented targets, the Al-content in the barrier layers of the superlattices was systematically varied in a range of 0.1 ≤ x ≤ 0.5 in a controlled and quasi-continuous manner. An in-depth investigation employing XRD 2θ-ω scans and reciprocal space map measurements on superlattices with different periods as well as single quantum well samples suggests coherent growth of the superlattices for application-relevant quantum well widths. The critical thickness for coherent growth of κ-Ga2O3 on κ-(AlxGa1−x)2O3 was further estimated to be at least 50 nm and 3 nm for x = 0.2 and x = 0.3, respectively. We determined absorption energies in optical transmission spectra for superlattices with x = 0.3 well below the bandgap of the barrier layers that decrease with increasing quantum well width suggesting transitions between localized states in the quantum wells as their origin. These results render superlattices in the metastable orthorhombic phase of Ga2O3 as a promising active layer for quantum well infrared photodetector applications.