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.

Novel approach to improve heat dissipation of AlGaN/GaN high electron mobility transistors with a Cu filled via under device active area

Abstract: A through Si-substrate via-hole under the active area of GaN-based HEMTs grown on Si substrates is proposed to reduce the maximum junction temperature. Due to the large lattice mismatch between Si and GaN, an AlN nucleation layer and an AlGaN transition layer are required to grow GaN layers on Si substrates. This AlN nucleation layer is very defective and thermally resistive. The proposed through Si-substrate via-hole offers access to this AlN nucleation layer from the back side of the wafer. By removing this highly thermally resistive layer and plating the via hole with copper, the maximum junction temperature can be reduced from 146 to 120 °C at a power density of 5 W/mm. Besides reducing the maximum junction temperature of the HEMT, this through Si-substrate via-hole can be electrically connected to the source contact and act as a backside source field plate to reduce the maximum electric field around the gate edges and thereby increase the drain breakdown voltage. If this through Si-substrate via-hole is connected to the front gate pad, it can also behave as a back gate to improve front gate modulation.

Band line-up and mechanisms of current flow in n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions

Abstract: The properties of n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions (HJ) prepared by hydride vapor phase epitaxy (HVPE) on 4H SiC substrates are reported. It is shown that the GaN/p-SiC HJ is staggered type II with the conduction bandoffset and the valence bandoffset values, respectively, ΔEc=−0.49 eV and ΔEv=0.65 eV. When changing GaN for AlGaN with Al mole fraction of x=0.25–0.3 the band alignment becomes normal type I with ΔEc=0.2 eV and ΔEv=0.6 eV. Current–voltage characteristics of both heterojunctions bear evidence of strong tunneling via defect states. The tunneling was found to be more pronounced in the AlGaN/SiC HJs even though these showed no evidence of formation of dark line defects at the interface, in contrast to GaN/SiC.

Effect of nanopillar sublayer embedded with SiO2 on deep traps in green GaN/InGaN light emitting diodes

Abstract: The effect of a layer of GaN nanopillars with SiO2 nanoparticles inserted into the n+-GaN contact Layer on the electrical properties, electroluminescence (EL) and photoluminescence (PL), admittance spectra, and deep trap spectra of green multi-quantum-well GaN/InGaN light emitting diodes (LEDs) grown by metalorganic chemical vapor deposition (MOCVD) on patterned sapphire substrates is reported. The PL and EL intensities for these SiO2 LEDs are measurably enhanced compared with reference to LEDs without the nanopillar sublayer. This correlates with the decrease in the SiO2 LEDs of the concentration of 0.25 eV electron traps and 0.45 eV hole traps, both located in the InGaN QWs.

60Co gamma ray damage in homoepitaxial β-Ga2O3 Schottky rectifiers

Abstract: β-Ga2O3 Schottky rectifiers consisting of thick (10 μm) epitaxial drift regions on conducting substrates are shown to have a high tolerance to 60Co gamma ray irradiation. This is due to the low carrier removal rate of <1 cm−1 for gamma rays, which contrasts to values of 300–500 cm−1 for MeV protons and alpha particles in the same rectifier structures. Changes in diode ideality factor, Schottky barrier height, on-resistance, on-off ratio, and reverse recovery time are all minimal for fluences up to 2 × 1016 cm−2 (absorbed dose of 100 kGy (Si)). These results are consistent with previous reports on gamma-irradiation of Ga2O3 metal oxide semiconductor field effect transistors (MOSFETs) where changes were ascribed to damage in the gate dielectric and not to the Ga2O3 itself.

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.