Stephen J. Pearton

Bio: Stephen J. Pearton is an academic researcher from University of Florida. The author has contributed to research in topics: Dry etching & Etching (microfabrication). The author has an hindex of 104, co-authored 1913 publications receiving 58669 citations. Previous affiliations of Stephen J. Pearton include Kyungpook National University & University of Southern California.

Nondestructive spectroscopic method to detect MnAs metallic nanocrystals in annealed GaAs:Mn

Abstract: We report an optical spectroscopic method to monitor NiAs-type MnAs (α-MnAs) nanocrystals in (Ga,Mn)As diluted magnetic semiconductors. We utilize Mn ion implantation of low temperature (LT) GaAs epitaxial thin films followed by rapid thermal annealing (RTA) to yield embedded ferromagnetic α-MnAs nanoclusters in a GaAs:Mn matrix. As-implanted samples are paramagnetic and become ferromagnetic with Curie temperature of ∼320 K after RTA at 750 °C. No peaks of potential secondary phases could be observed in x-ray diffraction measurements. However, in optical spectra, the annealed samples show resonant absorption at 0.9 eV photon energy, due to resonant surface plasma oscillation of spherical metallic phases embedded in LT GaAs. Since the absorption peak position in the photon energy has a direct relation to the value of the plasma frequency of metallic inclusions, the metallic clusters in LT GaAs are identified as α-MnAs nanocrystals by comparing them with simulations based on Maxwell–Garnett theory. We sugge...

Detection of C 2 H 4 Using Wide-Bandgap Semiconductor Sensors AlGaN/GaN MOS Diodes and Bulk ZnO Schottky Rectifiers

Abstract: The characteristics of SC 2 O 3 /AIGaN/GaN metal-oxide semiconductor (MOS) diodes and Pt/ZnO Schottky diodes as detectors of C 2 H 4 are reported. At 25°C, a change in forward current of ∼40 μA at a bias of 2.5 V was obtained in response to a change in ambient from pure N 2 to 10% C 2 H 4 J90% N 2 . The current changes are almost linearly proportional to the testing temperature and reach around 400 μA at 400°C. The mechanism of the change in forward gate current appears to be formation of a dipole layer at the oxide/AIGaN interface that screens some of the piezo-induced channel charge at the AIGaN/GaN interface. The ZnO diodes show no detectable change in current when exposed to ethylene at 25°C but exhibit large changes (up to 10 mA) at higher temperatures. In these diodes the detection mechanism appears to also involve introduction of hydrogen donors into the near-surface region of the ZnO, increasing the effective doping level under the rectifying contact.

Effect of 5 MeV proton radiation on DC performance and reliability of circular-shaped AlGaN/GaN high electron mobility transistors

Abstract: The authors report an investigation of the effect of different doses of 5 MeV proton irradiation on circular-shaped AlGaN/GaN high electron mobility transistors. The degradation of saturation drain current (IDSS) was minimal up to an irradiation dose of 2 × 1013 cm−2. By comparison, a dose of 2 × 1014 cm−2 dose produced a 12.5% reduction of IDSS and 9.2% increase of sheet resistance. In addition, the threshold voltage showed larger positive shifts for 2×1014 cm−2 dose compared to 2×1013 cm−2, and both of these doses produced showed larger shifts for smaller gate to drain distances. Increases of 39.8% and 47.1%, respectively, in the breakdown voltage for 6 and 10 μm drain to gate distances (LGD) was observed and was attributed to the creation of a virtual gate at the AlGaN/GaN interface due to the irradiation, which reduced the peak electric field at the drain side of the gate edge.

Integrated electronic circuitry and heat sink

Abstract: A multi-layer heatsink module for effecting temperature control in a three-dimensional integrated chip is provided. The module includes a high thermal conductivity substrate having first and second opposing sides, and a gallium nitride (GaN) layer disposed on the first side of the substrate. An integrated array of passive and active elements defining electronic circuitry is formed in the GaN layer. A metal ground plane having first and second opposing sides is disposed on the second side of the substrate, with the first side of the ground plane being adjacent to the second side of the substrate. A dielectric layer of low thermal dielectric material is deposited on the back side of the ground plane, and a metal heatsink is bonded to the dielectric layer. A via extends through the dielectric layer from the metal heatsink to the metal ground plane.

Comparison of ICl- and IBr-based plasma chemistries for inductively coupled plasma etching of GaN, InN and AlN

Abstract: A parametric study of the etch characteristics of GaN, AIN and InN has been earned out with IC1/Ar and IBr/Ar chemistries in an Inductively Coupled Plasma discharge. The etch rates of InN and AIN were relatively independent of plasma composition, while GaN showed increased etch rates with interhalogen concentration. Etch rates for all materials increased with increasing rf chuck power, indicating that higher ion bombardment energies are more efficient in enhancing sputter resorption of etch products. The etch rates increased for source powers up to 500 W and remained relatively thereafter for all materials, while GaN and InN showed maximum etch rates with increasing pressure. The etched GaN showed extremely smooth surfaces, which were somewhat better with IBr/Ar than with IC1/Ar. Maximum selectivities of- 14 for InN over GaN and >25 for InN over AIN were obtained with both chemistries.

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

Spintronics: Fundamentals and applications

Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

Graphene-based composites

Abstract: Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

Fundamentals of zinc oxide as a semiconductor

Abstract: In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.