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.

Pulsed laser deposition of high-quality ZnO films using a high temperature deposited ZnO buffer layer

Abstract: High-quality ZnO film growth on sapphire was achieved by pulsed laser deposition using a high temperature deposited ZnO buffer layer. This high temperature deposited buffer layer remarkably improves crystallinity of subsequent films. In particular, the full width at half-maximum of X-ray diffraction ω-rocking curves for ZnO films grown with the buffer layer is 0.0076° (27.36 arcsec) and 0.1242° (447.12 arcsec) for the out-of-plane (002) and in-plane (102) reflections, respectively. In addition, ZnO films grown with this buffer layer showed a carrier mobility of 88 cm2/V s, which is three times higher than that realized for ZnO films grown without the buffer layer. The room temperature photoluminescence spectra showed strong band edge emission with little or no defect-related visible emission.

Neutron irradiation effects in undoped n-AlGaN

Abstract: The effect of fast neutron (energy >0.1MeV) irradiation on electrical properties and deep level spectra of undoped n-AlGaN films with Al mole fraction x=0.4 are presented. In virgin samples, the properties are strongly influenced by deep traps at Ec−0.25eV present in high concentrations (∼2.5×1018cm−3). Neutron irradiation with doses higher than 1015cm−2 leads to compensation of these centers with a removal rate of about 500cm−1. After neutron irradiation with high dose of 1.7×1017cm−2 the samples become resistive (>104Ωcm), with the Fermi level pinned by new centers near Ec−0.35eV introduced by irradiation with a rate of about 10cm−1. The neutron irradiation also gives rise to an increase of the concentration of deep hole traps with activation energy of 1eV.

Fabrication of GaN nanostructures by a sidewall-etchback process

Abstract: GaN structures as small as 300 AA have been fabricated using conventional optical lithography by employing a deposition/selective etchback technique. After initial resist patterning conformal plasma-enhanced chemical vapour deposition or reactive sputtering of a metal (W or WSix) or a low temperature dielectric (SiNx or SiO2) is followed by an anisotropic etchback to leave a thin sidewall on the resist feature. The resist is then removed by dry etching, leaving the sidewall, which can be used as a mask for subsequent pattern transfer into the underlying GaN. Electron cyclotron resonance dry etching in CH4/H2/Ar discharges is shown to produce GaN nanostructures without any change in the near-surface stoichiometry of the material.

Temperature characteristics of 850 nm, intra-cavity contacted, shallow implant-apertured vertical-cavity surface-emitting lasers

Abstract: We have investigated the temperature characteristics of 850 nm, intra-cavity contacted, shallow implant-apertured, vertical-cavity surface-emitting lasers. The devices were fabricated with 7 μm diameter apertures and exhibited multimode behavior. Device lasing is observed up to 80 °C. The slope efficiency of the devices decrease from 0.29 to 0.20 W/A over the temperature range of 20–80 °C. From threshold temperature dependence data, the characteristic temperature is 78 °C. The fundamental optical mode of the devices shifts to longer wavelengths 0.11 nm/°C. The thermal resistance of the devices, determined experimentally, is 1.95 °C/mW.

Influence of ion mixing on the energy dependence of the ion-assisted chemical etch rate in reactive plasmas

Abstract: Recently, Stafford et al. [Appl. Phys. Lett. 87, 071502 (2005)] have shown that in contrast to the etch yield on a saturated surface, the ion-assisted chemical etch rate cannot universally be modeled by a simple square-root energy dependence. This results from the surface coverage by reactive neutral species being also a function of the ion energy. In this work, we further point out that depending on the plasma-material combination, the etch rate can exhibit two regimes that are characterized by different dependences on the ion energy. While these results are inconsistent with currently available models, we show that they can be interpreted by taking into account ion mixing effects on the desorption rate of volatile reaction products involved in the model of Stafford et al. Application of this rate model to the etching of Si, SiO2, HfO2, and ZrO2 in chlorine and fluorine plasma chemistries provides an excellent description of the simultaneous dependence of the etch rate on ion energy and on ion and reacti...

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.