Home  About us  Contact
 

Band Alignment (band + alignment)

Distribution by Scientific Domains
Physics and Astronomy75%
Polymers and Materials Science25%

Selected Abstracts

Band alignment at metal,semiconductor and metal,oxide interfaces

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010
John Robertson
Abstract The mechanisms of Schottky barrier formation are reviewed from the metal-induced gap state model to the universal defect model, and the chemical reaction model. The recent progress in understanding barrier heights and band offsets in Si , high dielectric constant oxide and metal high dielectric constant oxide systems is then discussed, and interesting they contain components of each model. The greater emphasis on understanding defect reactions has allowed us to separate the effects of intrinsic mechanisms, metal induced gap states (MIGS) and extrinsic mechanisms (defects). [source]

Thin Film Solar Cells: Materials Science at Interfaces

ADVANCED ENGINEERING MATERIALS, Issue 10 2005
J. Fritsche
Abstract Interfaces are important for the efficiencies of thin film solar cells. In particular for polycrystalline chalcogenide semiconductors as Cu(In,Ga)(S,Se)2 and CdTe the existing physical concepts, which describe the electronic properties of semiconductor interfaces, are not sufficient. The increased complexity is mostly due to the non-abruptness of the interfaces and the strong tendency for the formation of defects. For the CdTe thin film solar cell a very relevant interface for their operation and efficiency is the CdTe/CdS semiconductor hetero junction. The properties of the semiconductor interfaces have been characterised systematically with photoelectron spectroscopy (XPS/UPS) in integrated ultra high vacuum (UHV) systems for sample preparation and analysis. Withal the key topic is the experimental determination of the band alignment at the semiconductor interfaces. For high efficiency CdTe solar cell production CdCl2 activation is of major importance. The effects of the CdCl2 treatment step on CdTe solar cells had been not completely understood so far. To investigate its influence the activation process has been transferred into the integrated UHV system. We will report about chemical and electronic modifications of the CdTe/CdS hetero interface due to in-situ CdCl2 activation performing sputter depth profiles in combination with X-ray photoelectron spectroscopy (XPS). [source]

Exciton,Exciton Interaction and Optical Gain in Colloidal CdSe/CdS Dot/Rod Nanocrystals

ADVANCED MATERIALS, Issue 48 2009
Michele Saba
Exciton,exciton interaction in dot/rod CdSe/CdS nanocrystals has proved to be very sensitive to the shape of nanocrystals, due to the unique band alignment between CdSe and CdS. Repulsive exciton,exciton interaction is demonstrated, which makes CdSe/CdS dot/rods promising gain media for solution-processable lasers, with projected pump threshold densities below 1 kW cm,2 for continuous wave lasing. [source]

Infrared imaging with InAs/GaSb type-II superlattices

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2006
M. Walther
Abstract InAs/GaSb short period superlattices (SLs) with broken gap typ-II band alignment are very well suited for the fabrication of high performance infrared camera systems for the second atmospheric window (3,5 µm). High resolution focal plane arrays for single- and dual-colour applications based on InAs/GaSb SLs have been fabricated. Those camera systems reveal excellent performance data which are comparable and even superior to state of the art thermal imaging systems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optical characterization of Zn0.97Mn0.03Se/ZnSe0.92Te0.08 type II multiple-quantum-well structures

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007
D. Y. Lin
Abstract The optical characterization of type II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures have been studied using photoluminescence (PL), temperature-dependent PL, polarized PL, power-dependent PL, and photoreflectance (PR) in this study. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe system is type II. Comparing with the theoretical calculation based on the Schrodinger equation, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blueshift under different excitation power. The blueshift can be interpreted in terms of the band-bending effect due to spatially photoexcited carriers in a type II alignment. The thermal activation energy (EA) for quenching the PL intensity was determined from tem- perature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe and ZnSeTe layers decreased. The polarized PL spectra exhibit a large in-plane polarization with the polarization degree up to 50%. The polarization does not depend on the excitation intensity as well as temperature. The large polarization is an inherent orientation of the interface chemical bonds. The higher transition features observed in PR spectra show a blueshift with the similar trend observed in the PL spectra as decreasing the thickness of ZnSeTe layer. This result provides a consistent evidence for the assumption that square-like well shapes were built in the ZnSeTe layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A hybrid functional scheme for defect levels and band alignments at semiconductor,oxide interfaces

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010
Peter Broqvist
Abstract We introduce a theoretical scheme to study defect energy levels and band alignments at semiconductor,oxide interfaces. The scheme relies on hybrid functionals to overcome the band gap underestimation typically achieved with semilocal density functionals. For atomically localized defects, the more accurate description achieved with hybrid functionals does not lead to significant shifts of the charge transition levels, provided these levels are referred to a common reference potential. This result effectively decouples the shifts of the band edges with respect to the defect levels. We also show that relative shifts of conduction and valence band edges as determined by exact nonlocal exchange lead to band offsets in excellent agreement with experimental values for several semiconductor,oxide interfaces. The proposed scheme is illustrated through a series of applications, including the dangling bond defects in silicon and germanium, the charge state of the O2 molecule during silicon oxidation, and the oxygen vacancy in Si,SiO2,HfO2 stacks. [source]

Time-resolved photoluminescence of type-II InAs/GaAs quantum dots covered by a thin GaAs1,xSbx layer

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2009
Yu-An Liao
Abstract We investigate carrier lifetimes of InAs/GaAs quantum dots (QDs) covered by a thin GaAs1,xSbx layer by time-resolved photoluminescence (PL). Both the power dependent PL peak shift and the longer decay time confirm the type-II band alignments. Different recombination paths have been identified by temperature dependent measurements. At low temperatures, the long-range recombination with holes trapped in the GaAsSb layer is significant, resulting in non-single-exponential decays. The short-range recombination with holes confined in the band-bending region surrounding the InAs QDs is important at higher temperatures. The variation in decay time across the ground-state and the temporal PL peak redshift further confirm the localization of holes in the GaAsSb layer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]