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Band offset
About: Band offset is a research topic. Over the lifetime, 2446 publications have been published within this topic receiving 53450 citations.
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TL;DR: In this article, the authors developed a controlled synthesis of α-In2S3/In2O3 nanowire heterostructures by a hydrothermally assisted sulfurization process.
Abstract: Separation of photo-induced charges is crucial in controlling the performance of photocatalysts, photochemical cells, and photovoltaic devices. We developed a controlled synthesis of α-In2S3/In2O3 nanowire heterostructures by a hydrothermally assisted sulfurization process. Structural characterization reveals that two distinct nanowire heterostructures: α-In2S3 nanoparticles decorated In2O3 nanowires and α-In2S3/In2O3 core–shell nanowires were obtained by controlling the pH condition during the sulfurization process. Optical characterization results show α-In2S3/In2O3 nanowire heterostructures exhibit a significantly decreased visible light emission and enhanced visible light absorption compared with the pure In2O3 nanowires, revealing that an efficient photo-induced charge separation efficiency exists. The band offsets of the α-In2S3/In2O3 nanowire heterostructures were determined by X-ray photoemission spectroscopy and a type-II band alignment at the interface is confirmed. Time-resolved photoluminescence results reveal that the α-In2S3 nanoparticles/In2O3 nanowires exhibit significant photo-induced carrier lifetime improvement compare with the α-In2S3/In2O3 core–shell nanowire, due to a shorter charge carrier transport path, which ensures rapid charge separation at the interface. Because of the staggered band offset which promoted effective charge separation, the α-In2S3/In2O3 nanowire heterostructures exhibited enhanced photocatalytic activities under visible light illumination, demonstrating their promising potentials in relevant photo-conversion applications.
22 citations
TL;DR: In this article, the electron energy band alignment of a metal-oxide-semiconductor tunnel field effect transistor heterojunction, W/Al2O3/InGaAs/INAs/InP, is determined by internal photoemission spectroscopy.
Abstract: The electron energy band alignment of a metal-oxide-semiconductor tunnel field-effect transistor heterojunction, W/Al2O3/InGaAs/InAs/InP, is determined by internal photoemission spectroscopy. At the oxide flat-band condition, the barrier height from the top of the InGaAs/InAs valence band and the top of the InP valence band to the bottom of the Al2O3 conduction band is determined to be 3.5 and 2.8 eV, respectively. The simulated energy band diagram of the heterostructure is shown to be consistent with the measured band alignments if an equivalent positive charge of 6.0 × 1012 cm−2 is present at the Al2O3/InGaAs. This interface charge is in agreement with previously reported capacitance-voltage measurements.
22 citations
TL;DR: It is concluded that a Zn(1-x)Mg(x)O film with a relatively high bandgap energy is necessary to create a suitable conduction band offset at the Zn (1- x)Mng( x)O/CIGS interface to obtain a robust heterojunction.
Abstract: The electronic band structure at the Zn1−xMgxO/Cu(In0.7Ga0.3)Se2 interface was investigated for its potential application in Cd-free Cu(In,Ga)Se2 thin film solar cells. Zn1−xMgxO thin films with various Mg contents were grown by atomic layer deposition on Cu(In0.7Ga0.3)Se2 absorbers, which were deposited by the co-evaporation of Cu, In, Ga, and Se elemental sources. The electron emissions from the valence band and core levels were measured by a depth profile technique using X-ray and ultraviolet photoelectron spectroscopy. The valence band maximum positions are around 3.17 eV for both Zn0.9Mg0.1O and Zn0.8Mg0.2O films, while the valence band maximum value for CIGS is 0.48 eV. As a result, the valence band offset value between the bulk Zn1−xMgxO (x = 0.1 and x = 0.2) region and the bulk CIGS region was 2.69 eV. The valence band offset value at the Zn1−xMgxO/CIGS interface was found to be 2.55 eV after considering a small band bending in the interface region. The bandgap energy of Zn1−xMgxO films increased from 3.25 to 3.76 eV as the Mg content increased from 0% to 25%. The combination of the valence band offset values and the bandgap energy of Zn1−xMgxO films results in the flat (0 eV) and cliff (−0.23 eV) conduction band alignments at the Zn0.8Mg0.2O/Cu(In0.7Ga0.3)Se2 and Zn0.9Mg0.1O/Cu(In0.7Ga0.3)Se2 interfaces, respectively. The experimental results suggest that the bandgap energy of Zn1−xMgxO films is the main factor that determines the conduction band offset at the Zn1−xMgxO/Cu(In0.7Ga0.3)Se2 interface. Based on these results, we conclude that a Zn1−xMgxO film with a relatively high bandgap energy is necessary to create a suitable conduction band offset at the Zn1−xMgxO/CIGS interface to obtain a robust heterojunction. Also, ALD Zn1−xMgxO films can be considered as a promising alternative buffer material to replace the toxic CdS for environmental safety.
22 citations
TL;DR: In this paper, a conduction band cliff was found at the buffer/absorber interface and activation energy of the saturation current was smaller than the absorber band gap energy in the Mo/CuInS2/buffer/ZnO heterostructure solar cell.
Abstract: In the early 1990s, CuInS2 thin film solar cells with >10% efficiency had been developed. Since then, they are limited by an open-circuit voltage which is too low for the band gap of CuInS2. Recombination at the CdS/CuInS2 interface was made responsible for this shortcoming. This was concluded from two experimental results: a conduction band cliff found at the buffer/absorber interface and activation energy of the saturation current being smaller than the absorber band gap energy. However, replacing the CdS buffer layer in the Mo/CuInS2/buffer/ZnO heterostructure solar cell with wide gap buffers did not lead to substantially higher Voc. Also the activation energy was unaltered. In this paper, we discuss interface and bulk aspects of CuInS2 and Cu(In,Ga)S2 cells, try to give a consistent picture and make suggestions for novel experiments. Copyright © 2012 John Wiley & Sons, Ltd.
22 citations
TL;DR: In this paper, the sp3s* tight-binding method was used to investigate the electronic band structures of the strained CdTe/ZnTe(001) SLs versus the biaxial strain, layer thicknesses and VBO.
Abstract: The common-anion II–VI semiconductor superlattices (SLs) are characterized by a vanishing or a small valence-band offset (VBO). In the case of the lattice-mismatched SLs, the biaxial strain can drastically affect the splitting of the valence-band top states, and therefore be explored in designing type-I character SLs. In the present work, we used the sp3s* tight-binding method, with the inclusion of strain and spin–orbit coupling effects, to investigate the electronic band structures of the strained CdTe/ZnTe(001) SLs versus the biaxial strain, layer thicknesses and VBO. Our results show that the electron is always confined within the CdTe slabs, whereas the hole behaviour controls the whole SL character. Our theoretical results are compared to the photoluminescence experiments and shown to be consistent with the strain morphology along the SL growth direction as well as the optical and structural qualities of the experimental samples.
22 citations