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.
Spintronics is a large field of research that involves the generation, manipulation and detection of spin currents in magnetic heterostructures and the use of these currents to excite and to set the state of magnetic nano-elements. [1,2] The field of spintronics has focused on ferromagnetic thin film structures in which charge currents can be spin-polarized via interfacial and volume spin dependent scattering. However, ferromagnets produce magnetostatic dipole fields, which increase in size as devices are scaled to smaller dimensions. These must be minimized or eleminated to enable operation of spintronic field sensing and magnetic memories. [2] One way to do this is to take advantage of the phenomenon of long-range oscillatory interlayer coupling [3] to create synthetic antiferromagnetic heterostructures [1] or the use of ferrimagnetic materials such as rare-earthtransition metal alloys at their compensation point. [4] The latter ferrimagnetic materials are of special inerest because they can completely eliminate dipole fields volumetrically, even on the atomic scale. However, materials are needed that can operate over a wide temperature window and not solely at or in the vicinity of a compensation temperature. Here we show that Heusler compounds can be designed for this purpose.Heusler compounds, YZ X 2 (where X , Y are transition metals and Z is a main-group 2 element), are well known for their potential applications in spintronics, especially in spin-torque based devices. [5] These materials crystallize in both cubic and tetragonal crystal structures with multiple magnetic sub-lattices, and hence are good candidates for engineering a wide range of complex magnetic structures. In particular all the known tetragonal Heuslers are ferrimagnetic with at least two magnetic sub-lattices whose magnetizations are aligned anti-parallel to one another, or, as has been shown recently, can be non-collinear to one another. The Mn based tetragonal Heuslers are of particular interest because their magnetic ordering temperatures can be well above room temperature, but the magnetizations of their two sub-lattices are typically distinct, leading to a net uncompensated magnetization. One of the most interesting of these materials is Mn3Ga which has a Curie temperature of ~750 K. [6] By tuning the magnetization of the two sublattices in Mn3Ga by changes in composition, we propose that a fully compensated ferrimagnetic (CFI) Heusler is possible. To help identify the needed compositional variations we have carried out density functional calculations of the electronic structures of Mn3-xYxGa 1 0 x (at zero temperature) for the elements = Y Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au, which are non-magnetic or nearly non-magnetic when substituted into Mn3Ga. We show that in all these cases it is theoretically possible to obtain a CFI , which we have experimentally validated for the case of Y=Pt.The present calculation is based on the experimental lattice parameters of the bulk Mn 3 Ga lattice. [6] We find that a compensated mag...
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.%.
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.
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