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.

AlGaN/GaN Heterostructure Based Schottky Diode Sensors with ZnO Nanorods for Environmental Ammonia Monitoring Applications

Abstract: AlGaN/GaN heterostructure Schottky diodes with ZnO nanorod functionalization are shown to be capable of detecting NH3 balanced with air at a concentration of ∼0.3 ppm at 25◦C and ∼0.1ppm at 300◦C. The diodes show reproducible current response to repeated cycling of the NH3 exposure at all temperatures in this range. The diode current at fixed voltage decreased upon exposure to the NH3, which is opposite to what occurs with exposure to hydrogen. This suggests the detection mechanism involves reaction of ammonia with oxygen species on the ZnO nanorods, increasing the negative charge on the interface with AlGaN. The detection sensitivity displayed an activation energy of 0.071 eV and increased monotonically with ammonia concentration at all temperatures, from 3.36% (25◦C) to 12.59% (300◦C) for 2 ppm at a voltage of 5 V. The diodes could detect ammonia for either polarity applied bias. The absolute current change and sensitivity upon exposure to ammonia increased with measurement temperature. © The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0041807jss]

Critical issues of III–V compound semiconductor processing

Abstract: We review some of the key processing needs for fabrication of next-generation electronic and photonic devices from III–V semiconducctors. These include high rate plasma etching capable of smooth controlled pattern transfer, selective wet etching solutions for the InGaAlP and InGaAlN materials systems and improved ohmic and rectifying contacts. The achievement of high reliability and acceptable yields requires low thermal budgets and an absence of residual damage from deposition, etch or implant processes.

Study on the effects of proton irradiation on the dc characteristics of AlGaN/GaN high electron mobility transistors with source field plate

Abstract: The effects of proton irradiation dose on the dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with source field plates were studied. The HEMTs were irradiated with various protons doses ranging from 5 × 1012 to 5 × 1015 cm−2 at a fixed energy of 5 MeV. HEMTs irradiated with proton dose below 5 × 1013 cm−2 showed less than 2% degradation of either saturation drain current (IDSS) or transconductance (gm). Significant changes of these parameters were observed for the devices irradiated with doses above 5 × 1013 cm−2. HEMTs irradiated with the highest proton dose of 5 × 1015 cm−2 showed a reduction of IDSS and gm of 86% and 64.7%, and a positive Vth shift of 0.84 V, respectively. Despite the significant IDSS and gm reductions, the off-state drain breakdown voltage (VBR) was improved more than five times at this particular irradiation condition. The significant improvement of off-state drain breakdown voltage was attributed to the formation of a virtual gate at drain side of gate edge, which was the result of the generation of defect centers at AlGaN/GaN interface.

Use of ultraviolet/ozone cleaning to remove C and O from GaAs prior to metalorganic molecular beam epitaxy and metalorganic chemical vapor deposition

Abstract: Ultraviolet/ozone cleaning of GaAs substrates prior to metalorganic molecular beam epitaxy at 500 °C is shown to reduce the interfacial C and O concentrations by more than two orders of magnitude Metal‐semiconductor field‐effect transistors (MESFETs) utilizing this cleaning prior to growth of the component epitaxial layers display superior current voltage (I‐V) saturation characteristics compared to identical devices grown without the cleaning step By contrast, provided the GaAs surface is not contaminated with silicates, the atomic hydrogen generated at the growth surface during growth by metalorganic chemical vapor deposition (MOCVD) leads to lower O and C interfacial concentrations, thereby circumventing the need for ozone cleaning MESFETs grown by MOCVD with or without this cleaning have excellent I‐V characteristics

Materials and Process Development for ZnMgO/ZnO Light-Emitting Diodes

Abstract: We report on the fabrication of UV LEDs based on a p-n junction p-ZnMgO/n-ZnO/n-ZnMgO double heterostructure. Pulsed-laser deposition was used to grow the complete heterostructure on c -plane sapphire templates. The LEDs were patterned by simple wet etching. Band-edge electroluminescence emission most likely associated with ZnO excitonic transitions was observed at room temperature. However, the devices show sensitivity to the presence of hydrogen in the measurement ambient due to formation of a surface conduction layer. The results show the potential of ZnO-based materials for UV emitters of potentially lower cost and with comparable or higher emission intensity than AlGaN/GaN devices provided adequate surface passivation techniques are developed.

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.