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.

Electrical properties of GaN (Fe) buffers for AlGaN∕GaN high electron mobility transistor structures

Abstract: The electrical properties of AlGaN∕GaN high electron mobility transistor structures grown on composite GaN(Fe)∕GaN buffers by molecular beam epitaxy were reported. The concentration of Fe in the GaN(Fe) layer ranged from 8×1016to3×1017cm−3 as established by secondary ion mass spectrometry. The thickness of the undoped GaN layer of the buffer was varied from 2.2to4.1μm. For thinner buffers and higher Fe concentration, the buffer was semi-insulating, with the Fermi level pinned near Ec-0.57eV. For thicker buffers and lower Fe concentration, the top part of the buffer was conducting. Admittance spectra measured in conducting buffers also showed a prominent contribution from Ec-(055–0.6)eV electron traps. Despite the universal prominence of these traps in all our films, the behavior of their concentration with Fe doping and with increased distance from the GaN (Fe)∕GaN boundary is not compatible with the assumption that they are due to substitutional Fe acceptors. Possible compensation mechanisms in the studi...

Effects of high dose Ni, Fe, Co, and Mn implantation into SnO2

Abstract: The effects of high dose (3 3 1016 cm22) implantation of Ni, Fe, Co, or Mn ions into bulk, single-crystal SnO2 substrates carried out at substrate temperature of ;350 C to avoid amorphization of the implanted region on the magnetic properties of the material are reported. X-ray diffraction showed no evidence of secondary phase formation in the SnO2 . The Mn-implanted samples remained paramagnetic, as also reported for samples doped during thin film growth, but the Fe, Co-, and Ni-implanted SnO2 showed evidence of hysteresis with approximate Curie temperatures of ;120 K ~Co and Cr! or 300 K ~Fe!. The carrier density in the implanted region appears to be too low to support carrier-mediated origin of the ferromagnetism and formation of bound magnetic polarons may be one explanation for the observed magnetic properties. The much reduced Curie temperature seen in Co-implanted SnO2 compared to material doped during pulsed laser deposition suggests the residual implant damage degrades the magnetic properties.

Electrical and recombination properties and deep traps spectra in MOCVD ELOG GaN layers

Abstract: Electrical properties, deep levels spectra, spectra of microcathodoluminescence, diffusion lengths of minority carriers were studied in undoped GaN films grown by standard metallorganic chemical vapour deposition on sapphire and by the epitaxial lateral overgrowth technique (ELOG) It is shown that the total concentrations of shallow donors and of electron and hole traps are very considerably lower in the ELOG material compared to the ordinary MOCVD samples MCL and electron beam induced current EBIC imaging of ELOG samples suggests that the dislocation density in the overgrown regions is on the order of 106 cm–2 while in-between these regions it is similar to the dislocation density in the standard material, about 109 cm–2 Local diffusion lengths were shown to follow the same trend as dislocation densities (© 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

Long-term stability study of botulinum toxin detection with AlGaN/GaN high electron mobility transistor based sensors

Abstract: The long-term stability of antibody-functionalized, Au-gated AlGaN/GaN high electron mobility transistors for detecting botulinum toxin is reported in this study. The botulinum toxin sensor, which initially showed good data reproducibility and recyclability, was repeatedly tested over a 9-month period. The botulinum sensor was packaged and stored in phosphate buffered saline (PBS) at 4 °C in a refrigerator for long-term storage. The sensor was tested over time at room temperature and we found sensitivity losses of 2%, 12% and 28% after 3, 6 and 9 months, respectively. These results clearly demonstrate a significant step towards the realization of electronic detection of biomolecules by field-deployed sensor chips based on AlGaN/GaN HEMTs.

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.