Surface states

About: Surface states is a research topic. Over the lifetime, 11143 publications have been published within this topic receiving 307395 citations.

Characteristics of high efficiency dye-sensitized solar cells.

Abstract: Impedance spectroscopy was applied to investigate the characteristics of dye-sensitized nanostructured TiO 2 solar cells (DSC) with high efficiencies of light to electricity conversion of 11.1% and 10.2%. The different parameters, that is, chemical capacitance, steady-state transport resistance, transient diffusion coefficient, and charge-transfer (recombination) resistance, have been interpreted in a unified and consistent framework, in which an exponential distribution of the localized states in the TiO 2 band gap plays a central role. The temperature variation of the chemical diffusion coefficient dependence on the Fermi-level position has been observed consistently with the standard multiple trapping model of electron transport in disordered semiconductors. A Tafel dependence of the recombination resistance dependence on bias potential has been rationalized in terms of the charge transfer from a distribution of surface states using the Marcus model of electron transfer. The current-potential curve of the solar cells has been independently constructed from the impedance parameters, allowing a separate analysis of the contribution of different resistive processes to the overall conversion efficiency.

Polarization effects, surface states, and the source of electrons in AlGaN/GaN heterostructure field effect transistors

Abstract: The origin of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructure field effect transistors is examined theoretically and experimentally. Based on an analysis of the electrostatics, surface states are identified as an important source of electrons. The role of the polarization-induced dipole is also clarified. Experimental Hall data for nominally undoped Al0.34Ga0.66N/GaN structures indicate that ∼1.65 eV surface donors are the actual source of the electrons in the 2DEG, which forms only when the barrier thickness exceeds 35 A.

Theory of Surface States

Abstract: The properties of metal-to-semiconductor junctions and of free semiconductor surfaces are usually explained on the basis of surface states. The theory of the metal contacts is discussed critically, because strictly speaking localized surface states cannot exist in such junctions. However, it is shown that virtual or resonance surface states can exist which behave for practical purposes in the same way. They are really the tails of the metal wave functions rather than separate states. In the past, the length of this tail has often been ignored. Some estimates of its length are made and its consequences pointed out. A semiquantitative discussion is given of various recent data, including the effect of an oxide layer on barrier height, the variation of barrier height with the metal, the work function of a free surface at high doping, and the effect of a cesium layer on the work function.

Semiconductor surfaces and interfaces

Abstract: 1 Introduction- 2 Surface Space-Charge Region in Thermal Equilibrium- 3 Surface States- 4 Occupation of Surface States and Surface Band-Bending in Thermal Equilibrium- 5 Surface S pace-Charge Region in Non-Equilibrium- 6 Interface States- 7 Cleaved {110} Surfaces of III-V and II-VI Compound Semiconductors- 8 {100} Surfaces of III-V, II-VI, and I-VII Compound Semiconductors with Zincblende Structure- 9 {100} Surfaces of Diamond, Silicon, Germanium, and Cubic Silicon Carbide- 10 Diamond, Silicon, and Germanium {111}-2 x 1 Surfaces- 11 Si(111)-7 x 7 and Ge(111)-c(2 x 8) Surfaces- 12 Phase Transitions on Silicon and Germanium {111} Surfaces- 13 {111} Surfaces of Compounds with Zincblende Structure- 14 Monovalent Adatoms- 15 Group-III Adatoms on Silicon Surfaces- 16 Group-V Adatoms- 17 Oxidation of Silicon and III-V Compound Semiconductors- 18 Surface Passivation by Adsorbates and Surfactants- 19 Semiconductor Interfaces- References- Index of Reconstructions and Adsorbates

Imaging standing waves in a two-dimensional electron gas

Abstract: ELECTRONS occupying surface states on the close-packed surfaces of noble metals form a two-dimensional nearly free electron gas1–3. These states can be probed using the scanning tunnelling microscope (STM), providing a unique opportunity to study the local properties of electrons in low-dimensional systems4. Here we report the direct observation of standing-wave patterns in the local density of states of the Cu(lll) surface using the STM at low temperature. These spatial oscillations are quantum-mechanical interference patterns caused by scattering of the two-dimensional electron gas off step edges and point defects. Analysis of the spatial oscillations gives an independent measure of the surface state dispersion, as well as insight into the interaction between surface-state electrons and scattering sites on the surface.