Flexible hardware concept of pulsed laser deposition for large areas and combinatorial composition spreads.

Pulsed laser deposition (PLD) is one of the most flexible physical growth techniques for thin films of functional materials at the research and demonstrator level. We describe here a relatively simple and reliable concept of the PLD hardware that allows both deposition on large areas up to 4 in. diameter and deposition of tailored lateral and vertical composition spreads without time-consuming hardware changes.

Growth of κ-([Al,In]Ga)O Quantum Wells and Their Potential for Quantum-Well Infrared Photodetectors.

The wide band gap semiconductor κ-GaO 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/AlGaAs quantum-well infrared photodetectors (QWIPs) could be substantially excelled with about 1-100 μm using κ-([Al,In]Ga)O, 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.

Suppression of Rotational Domains of CuI Employing Sodium Halide Buffer Layers.

The occurrence of rotational domains is a well-known issue for copper iodide (CuI) that naturally occurs for growth on popular substrates like sapphire. However, this has detrimental effects on the thin film quality like increasing surface roughness or deteriorated transport characteristics due to grain boundary scattering. Utilizing pulsed laser deposition and the growth of sodium chloride (NaCl) and sodium bromide (NaBr) template layers, studies were performed on their potential on suppressing the formation of rotational domains of CuI on c-plane sapphire and SrF(111) substrates.

Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors.

The electronic and optical properties of (InGa)O alloys are highly tunable, giving rise to a myriad of applications including transparent conductors, transparent electronics, and solar-blind ultraviolet photodetectors. Here, we investigate these properties for a high quality pulsed laser deposited film which possesses a lateral cation composition gradient (0.01 ≤ ≤ 0.

Band Offsets at κ-([Al,In]Ga)O/MgO Interfaces.

Conduction and valence band offsets are among the most crucial material parameters for semiconductor heterostructure device design, such as for high-electron mobility transistors or quantum well infrared photodetectors (QWIP). Because of its expected high spontaneous electrical polarization and the possibility of polarization doping at heterointerfaces similar to the AlGaN/InGaN/GaN system, the metastable orthorhombic κ-phase of GaO and its indium and aluminum alloy systems are a promising alternative for such device applications. However, respective band offsets to any dielectric are unknown, as well as the evolution of the bands within the alloy systems.

Native Point Defect Measurement and Manipulation in ZnO Nanostructures.

This review presents recent research advances in measuring native point defects in ZnO nanostructures, establishing how these defects affect nanoscale electronic properties, and developing new techniques to manipulate these defects to control nano- and micro- wire electronic properties. From spatially-resolved cathodoluminescence spectroscopy, we now know that electrically-active native point defects are present inside, as well as at the surfaces of, ZnO and other semiconductor nanostructures. These defects within nanowires and at their metal interfaces can dominate electrical contact properties, yet they are sensitive to manipulation by chemical interactions, energy beams, as well as applied electrical fields.

Processing Strategies for High-Performance Schottky Contacts on n-Type Oxide Semiconductors: Insights from InO.

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (InO), is often challenged by the presence of a distinct surface electron accumulation layer. We investigated the material properties and electrical transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the preparation of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evaporation and (reactive) sputtering in an (O and) Ar atmosphere, with oxygen plasma interface treatments, we identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio.

Defect Manipulation To Control ZnO Micro-/Nanowire-Metal Contacts.

Surface states that induce depletion regions are commonly believed to control the transport of charged carriers through semiconductor nanowires. However, direct, localized optical, and electrical measurements of ZnO nanowires show that native point defects inside the nanowire bulk and created at metal-semiconductor interfaces are electrically active and play a dominant role electronically, altering the semiconductor doping, the carrier density along the wire length, and the injection of charge into the wire. We used depth-resolved cathodoluminescence spectroscopy to measure the densities of multiple point defects inside ZnO nanowires, substitutional Cu on Zn sites, zinc vacancy, and oxygen vacancy defects, showing that their densities varied strongly both radially and lengthwise for tapered wires.

Combinatorial Material Science and Strain Engineering Enabled by Pulsed Laser Deposition Using Radially Segmented Targets.

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.

Vital Role of Oxygen for the Formation of Highly Rectifying Schottky Barrier Diodes on Amorphous Zinc-Tin-Oxide with Various Cation Compositions.

We present electrical properties of Schottky barrier diodes on room-temperature deposited amorphous zinc-tin-oxide (ZTO) with Zn/(Zn + Sn) contents between 0.12 and 0.72.

Influence of the Cation Ratio on Optical and Electrical Properties of Amorphous Zinc-Tin-Oxide Thin Films Grown by Pulsed Laser Deposition.

Continuous composition spread (CCS) methods allow fast and economic exploration of composition dependent properties of multielement compounds. Here, a CCS method was applied for room temperature pulsed laser deposition (PLD) of amorphous zinc-tin-oxide to gain detailed insight into the influence of the zinc-to-tin cation ratio on optical and electrical properties of this ternary compound. Our CCS approach for a large-area offset PLD process utilizes a segmented target and thus makes target exchange or movable masks in the PLD chamber obsolete.

Interface recombination current in type II heterostructure bipolar diodes.

Wide-gap semiconductors are often unipolar and can form type II bipolar heterostructures with large band discontinuities. We present such diodes with very high rectification larger than 1 × 10(10). The current is assumed to be entirely due to interface recombination.

Tungsten oxide as a gate dielectric for highly transparent and temperature-stable zinc-oxide-based thin-film transistors.

Tungsten oxide is currently used as gate insulator in pH-sensing ion-sensitive field-effect transistors (ISFETs) and in electrochromic devices. Its great potential as a high-κ dielectric with high transparency and temperature stability is reported. Owing to the low gate voltage sweep necessary to turn the transistor on and off, a possible application could be as a low-voltage pixel driver in active-matrix displays in harsh environments.

Recent progress on ZnO-based metal-semiconductor field-effect transistors and their application in transparent integrated circuits.

Metal-semiconductor field-effect transistors (MESFETs) are widely known from opaque high-speed GaAs or high-power SiC and GaN technology. For the emerging field of transparent electronics, only metal-insulator-semiconductor field-effect transistors (MISFETs) were considered so far. This article reviews the progress of high-performance MESFETs in oxide electronics and reflects the recent advances of this technique towards transparent MESFET circuitry.