Properties Of Wide Bandgap Materials Research Articles

Engineering Route for Stretchable, 3D Microarchitectures of Wide Bandgap Semiconductors for Biomedical Applications

AbstractWide bandgap (WBG) semiconductors have attracted significant research interest for the development of a broad range of flexible electronic applications, including wearable sensors, soft logical circuits, and long‐term implanted neuromodulators. Conventionally, these materials are grown on standard silicon substrates, and then transferred onto soft polymers using mechanical stamping processes. This technique can retain the excellent electrical properties of wide bandgap materials after transfer and enables flexibility; however, most devices are constrained by 2D configurations that exhibit limited mechanical stretchability and morphologies compared with 3D biological systems. Herein, a stamping‐free micromachining process is presented to realize, for the first time, 3D flexible and stretchable wide bandgap electronics. The approach applies photolithography on both sides of free‐standing nanomembranes, which enables the formation of flexible architectures directly on standard silicon wafers to tailor the optical transparency and mechanical properties of the material. Subsequent detachment of the flexible devices from the support substrate and controlled mechanical buckling transforms the 2D precursors of wide band gap semiconductors into complex 3D mesoscale structures. The ability to fabricate wide band gap materials with 3D architectures that offer device‐level stretchability combined with their multi‐modal sensing capability will greatly facilitate the establishment of advanced 3D bio‐electronics interfaces.

Ultrafast response of cubic silicon carbide to intense attosecond pulse light

In this paper we are motivated to numerically investigate the fundamental strong-field and attosecond response processes in wide band-gap solids, using the first-principle approach based on time-dependent density functional theory, advancing our understanding of fundamental strong-field and attosecond physics in solids. Taking cubic silicon carbide as a concrete example, the influence of pulse parameters on the ultrafast responses is demonstrated, which allows one to gain a useful independent insight into the interaction processes of attosecond light pulses with solids, revealing information currently not accessible by experiment. We also demonstrate control of the charge transfer and dielectric permittivity by intense attosecond pulse light. It is concluded that a single-cycle attosecond pulse light can be used to effectively manipulate the charge transfer and dielectric properties of wide-band gap materials with great potential for ultrafast device applications.

Manipulation of the dielectric properties of diamond by an ultrashort laser pulse

The dielectric properties of diamond in excited state modulated by an ultrashort and intense single-cycle laser field are investigated based on the real-time time-dependent density functional theory. The electron dynamics of diamond is analyzed within ultrashort time resolution. The change of dielectric properties are demonstrated by studying the effect of easily tunable laser parameters including intensity, frequency, and duration time. The extracted dielectric function shows anisotropy even in an centrosymmetric diamond when going beyond the linear response regime. We also demonstrate control of the dielectric functions by the delay time between pump and probe pulse. It is concluded that a tailored single-cycle laser field can be used to effectively manipulate the dielectric properties of wide-band gap materials.

The role of defects on the structural and magnetic properties of Nb2O5

Defects play a fundamental issue on physical properties of wide bandgap materials. We present here the effect of preparation and annealing conditions on the properties of Nb2O5 synthesized by Pechini method. Structural characterization, Raman spectroscopy and magnetic measurements show significant experimental fingerprints related to the presence of oxygen defects in the system. The increase of oxygen vacancies causes an irreversible phase transition from pseudohexagonal (TT-phase) to orthorhombic phase (T-phase). The critical temperature range around 400 °C during thermal annealing is derived by in-situ Raman measurements applying the theory of phonon anharmonicity. We observed that the values of Nb2O5 Curie constants as (4.37 ± 0.06)10−4 emu K/mol and (20.50 ± 0.08)10−4 emu K/mol for TT- and T-phases respectively. The oxygen vacancies are the responsible for 1021–1022 effective magnetic moments per mol related to paramagnetic behavior.

Luminescent properties of wide bandgap materials at room temperature

Properties of nanocrystalline thin films of selected nitrides are discussed as possible buffer materials for obtaining freestanding GaN wafers. These films are grown by impulse plasma deposition on silicon substrates. We demonstrate high smoothness of these films. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cold emission characterization using secondary electron emission spectroscopy

Secondary electron emission spectroscopy is used to study the electron transport and emission properties of wide bandgap materials (e.g., diamond, BeO). The secondary electron distribution generated in diamond is found to be dominated by a high concentration of very low-energy electrons, and the emission characteristics of these low-energy electrons is used to deduce information about the cold emission properties of the material. In particular, analysis of the extremely high yields measured from diamond samples indicates that the low-energy electrons have long escape depths in the material. Furthermore, electron energy distribution measurements provide insight into the emission process at various surfaces. The electron transport and emission model inferred from the diamond measurements suggests that diamond and other wide bandgap materials may be promising cold emitter materials, in which case secondary electron emission spectroscopy can be a useful characterization tool.