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.

Properties of (Ga, Mn)N With and Without Detectable Second Phases

Abstract: (Ga, Mn)N layers were grown by radio-frequency plasma-assisted molecular beam epitaxy with Mn concentrations of ~5 or 50 atom %. In the material doped with 5 atom % Mn, the growth conditions were adjusted to produce second phases in one case, detectable by X-ray diffraction. Under our conditions, the dominant second phases are -related and not All three types of material (single-phase or GaMn second phases at different concentrations) exhibit 300 K hysteresis in magnetic moment vs. field (M-H) plots, but the temperature dependence of the field-cooled (FC) and zero-field cooled (ZFC) magnetization is quite different in each case. A clear difference in FC-ZFC magnetization at 300 K in the single-phase material is observed. © 2003 The Electrochemical Society. All rights reserved.

Modeling and Fabrication of ZnO Nanowire Transistors

Abstract: ZnO is attracting attention for application in transparent nanowire (NW) transistors because of the ease of synthesis of ZnO nanostructures, their good transport properties, the availability of heterostructures, and the possibility for optoelectronic integration. A variety of both top and bottom gate n-type ZnO NW transistors have been reported, showing generally high on/off ratios (104 - 107), subthreshold voltage swings of 130-300 mV/dec, and excellent drain-current saturation. Much higher electron mobilities and improved device stability are found when surface passivation is employed, pointing to the importance of controlling surface charge density. Simulations show that defects such as grain boundaries lead to a decrease of drain current. While the dc characteristics of such devices are generally reasonable, there have been no reports of the RF or high-speed switching performance. Additional work is needed on optimized gate dielectrics, reliability, and functionality of ZnO NW transistors.

Properties of undoped GaN/InGaN multi-quantum-wells and GaN/InGaN p-n junctions prepared by epitaxial lateral overgrowth

Abstract: High resolution x-ray diffraction, electron beam induced current, capacitance-voltage profiling, admittance spectroscopy, deep level transient spectroscopy (DLTS), microcathodoluminescence (MCL) spectra and imaging were performed for multi-quantum-well (MQW) GaN/InGaN p-n junctions grown on epitaxial laterally overgrown (ELOG) n-GaN platform layers. These experiments show a very good crystalline quality of the MQW ELOG GaN/InGaN structures with a dislocation density of ∼106 cm−2 in the laterally overgrown ELOG wings regions. Admittance and DLTS spectra show the presence of a prominent electron-trap signal with activation energy ∼0.4 eV likely originating from electron activation from the lowest occupied state in the quantum wells. MCL spectra clearly show a redshift of luminescence in the laterally grown ELOG wings compared to the normally grown ELOG windows. Modeling based on solving Poisson–Schroedinger equations suggests that the main reason for the observed redshift is a higher indium content in the w...

Specific contact resistance of Ti/Al/Pt/Au ohmic contacts to phosphorus-doped ZnO thin films

Abstract: The carrier concentration dependence of Ti/Al/Pt/Au ohmic contact resistance on P-doped n-type ZnO thin films is reported. Ti (200 A)/Al (800 A)/Pt (400 A)/Au (800 A) was deposited by electron-beam evaporation on ZnO thin films grown by pulsed laser deposition on (0001) sapphire substrates using a ZnO:P0.02 source. Postgrowth annealing from 30 to 600 °C resulted in carrier concentrations of 7.5×1015 cm−3–1.5×1020 cm−3 in the ZnO. After metal deposition, the specific contact resistances were measured at temperatures in the range 30–100 °C prior to alloying annealing at 200 °C and at 30–200 °C after this anneal. The lowest specific contact resistance of 8.7×10−7 Ω cm2 for nonalloyed ohmic contacts was achieved in the sample with carrier concentration of 1.5×1020 cm−3 when measured at 30 °C. In the annealed samples, minimum specific contact resistances of 3.9×10−7 Ω cm2 and 2.2×10−8 Ω cm2 were obtained in samples with carrier concentrations of 6.0×1019 cm−3 measured at 30 °C and 2.4×1018 cm−3 measured at 200...

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.