Showing papers on "Band offset published in 2011"
TL;DR: In this paper, the authors developed a general model of the band offset at metal/ferroelectric interfaces and showed that, depending on the polarization of the film, a pathological regime might occur where the metallic carriers populate the energy bands of the insulator, making it metallic.
Abstract: Based on recent advances in first-principles theory, we develop a general model of the band offset at metal/ferroelectric interfaces. We show that, depending on the polarization of the film, a pathological regime might occur where the metallic carriers populate the energy bands of the insulator, making it metallic. As the most common approximations of density functional theory are affected by a systematic underestimation of the fundamental band gap of insulators, this scenario is likely to be an artifact of the simulation. We provide a number of rigorous criteria, together with extensive practical examples, to systematically identify this problematic situation in the calculated electronic and structural properties of ferroelectric systems. We discuss our findings in the context of earlier literature studies, where the issues described in this work have often been overlooked. We also discuss formal analogies to the physics of polarity compensation at LaAlO${}_{3}$/SrTiO${}_{3}$ interfaces, and suggest promising avenues for future research.
120 citations
TL;DR: In this paper, ZnO1−−xSx thin films were prepared by co-sputtering of znO and ZnS targets and they were used as the buffer layer in CIGS solar cells.
78 citations
TL;DR: In this paper, the authors investigated intermixing and electronic structure at thin (3-5 unit cells), epitaxial La1 − xAl1 + xO3/SrTiO3(001) heterojunctions for x = 0 and ± 0.05.
73 citations
TL;DR: In this paper, the authors measured the energy band offset at the heterointerface of semiconductor heterostructures, particularly in solar photovoltaic devices, using X-ray photoelectron spectroscopy and capacitance-voltage measurements.
59 citations
TL;DR: In this paper, an organic photodetector (PD) was demonstrated to detect 808nm radiation in near infrared (NIR) region, where the photodiode has a hybrid planar-mixed heterojunction structure.
59 citations
TL;DR: The presently unknown band offset in nonpolar cubic GaN/AlN superlattices is investigated by inter-sub-band and interband spectroscopies as well as ab initio calculations.
Abstract: The presently unknown band offset in nonpolar cubic GaN/AlN superlattices is investigated by inter-sub-band and interband spectroscopies as well as ab initio calculations On one hand, the conduction-band offset (CBO) has been determined from the comparison of the measured transition energies with model calculations within the effective mass approximation On the other hand, the valence-band offset (VBO) and the CBO are accurately simulated by calculating many-body corrections within the $\mathit{GW}$ approximation on top of hybrid-functional density functional theory calculations Thus, a CBO of $(14\ifmmode\pm\else\textpm\fi{}01) \mathrm{eV}$ and a VBO of $(05\ifmmode\pm\else\textpm\fi{}01) \mathrm{eV}$ is obtained as a result of both approaches
48 citations
TL;DR: In this paper, X-ray photoelectron spectroscopy was used to measure the valence-band offset (VBO) of the NiO/ZnO heterojunction grown on quartz substrate by radio frequency (RF) magnetron sputtering.
45 citations
TL;DR: Hybrid screened density functional theory as discussed by the authors better describes the electronic structure of HgTe, CdTe, and HgCdTe systems in comparison with standard density functional theories.
Abstract: Hybrid screened density functional theory better describes the electronic structure of HgTe, CdTe, and HgCdTe systems in comparison with standard density functional theory. The unique hybrid functional reproduces the band inversion in the popular HgCdTe alloy, justifying it as a better method than standard density functional theory in the search for different topological insulators. In addition, the 0.53-eV valence-band offset obtained using the hybrid functional supports the recently observed higher band offset in the HgTe/CdTe heterostructure.
41 citations
TL;DR: In this paper, the band offset at the Cu2O/ZnO heterojunction was estimated both experimentally and theoretically following the procedure of core-level spectroscopy.
Abstract: The band offset at the Cu2O/ZnO heterojunction was estimated both experimentally and theoretically following the procedure of core-level spectroscopy. The heterojunction was fabricated by electrochemical deposition, and the band offset was determined by X-ray photoelectron spectroscopy. For the theoretical calculation of the band offset, the first-principles, density-functional, pseudopotential method was used. It was predicted from both the experimental and calculation results that the valence band maximum of Cu2O is located higher than that of ZnO. The experimentally obtained valence band offset ΔEv was 1.7 eV, and the theoretically obtained ΔEv was 1.3–1.6 eV; both results agreed fairly well.
36 citations
TL;DR: In this article, the authors used a systematic approach for EWF extraction, combined with a comparison to unpinned SiO${}_{2}$ references, and found that no intrinsic FLP exists in the model dielectric Al${}-AlO{}-O{3}.
Abstract: Disparities between the predicted and the measured effective work functions (EWFs) in advanced metal oxide semiconductor devices, or Fermi-level pinning (FLP), have gained significant attention when high-$k$ dielectrics began to emerge. Using a systematic approach for EWF extraction, combined with a comparison to unpinned SiO${}_{2}$ references, it was found that no intrinsic FLP exists in the model dielectric Al${}_{2}$O${}_{3}$. Extrinsic FLP was found with one of the metals investigated Ta, where a 0.4 eV increase in the EWF was observed in the electrical characteristics and confirmed by backside spectroscopy. The physical origins of the band offsets related to the EWF increase have been analyzed in detail. A 2-nm interfacial layer at the Ta-Al${}_{2}$O${}_{3}$ interface has been found and is suggested as the source of extrinsic FLP. Interfacial dipoles originating from Ta-O chemical bonds are considered as the mechanism responsible for the band offset. The results of this model system are then used to explain some of the peculiarities occurring at complex devices which are used in technological applications.
34 citations
TL;DR: In this article, photo-ionization/neutralization and capacitance spectroscopy were used to determine the energy band alignment between 2.6-nm-diameter Si nanocrystals and the SiO2 host.
Abstract: The determination of the energy band alignment between the 2.6-nm-diameter Si nanocrystals and the SiO2 host is achieved by means of photo-ionization/-neutralization and capacitance spectroscopy. The measured conduction and valence band offsets are 2.6 eV and 4.4 eV. The band gap is evaluated to be 1.7 eV by photoluminescence. These results indicate that the valence band offset at the Si nanocrystals/SiO2 interface is quite close to the one observed at bulk Si/SiO2 interface. On the contrary, we observe a clear upward shift (0.5 eV) of the conduction band in the Si nanocrystals/SiO2 system with respect to the bulk Si/SiO2 hetero-structure.
TL;DR: In this article, the authors used x-ray photoelectron spectroscopy to determine the valence band offset (VBO) of a Cu2O/In2O3 heterojunction.
Abstract: In2O3 is a promising partner of Cu2O to form a Cu2O/In2O3 heterojunction system. We used x-ray photoelectron spectroscopy to determine the valence band offset (VBO) of a Cu2O/In2O3 heterojunction. The valence band offset is found to be 1.43 ± 0.2 eV. Given the experimental bandgaps of 2.0 eV and 2.6 eV for Cu2O and In2O3, respectively, we calculate the band alignment of a Cu2O/In2O3 heterojunction with a conduction band offset (CBO) of 0.83 ± 0.2 eV. To apply Cu2O/In2O3 bilayers in electronic devices, it is important to determine the band alignment accurately based on the VBO and CBO.
TL;DR: X-ray photoelectron spectroscopy has been used to measure the valence band offset of the InN/BaTiO3 heterojunction and it is found that a type-I band alignment forms at the interface.
Abstract: X-ray photoelectron spectroscopy has been used to measure the valence band offset of the InN/BaTiO3 heterojunction. It is found that a type-I band alignment forms at the interface. The valence band offset (VBO) and conduction band offset (CBO) are determined to be 2.25 ± 0.09 and 0.15 ± 0.09 eV, respectively. The experimental VBO data is well consistent with the value that comes from transitivity rule. The accurate determination of VBO and CBO is important for use of semiconductor/ferrroelectric heterojunction multifunctional devices.
TL;DR: In this paper, a double heterojunction bipolar transistor (DHBT)-based capacitorless one-transistor (1T) DRAM cell employing a narrow bandgap SiGe body and Si/SiGe Heterojunction for a possible next-generation DRAM cells was proposed.
Abstract: We propose a novel double heterojunction bipolar transistor (DHBT)-based capacitorless one-transistor (1T) DRAM cell employing a narrow bandgap SiGe body and Si/SiGe heterojunction for a possible next-generation DRAM cell. It has a body with a narrow bandgap and a valence band offset between the source/drain and the body. Through an extended investigation via TCAD simulation, we verified the advantages of the proposed DHBT-based 1T DRAM cell, including an improved excess carrier generation rate, a high current gain, a large sensing margin, and a suppressed sensitivity to the bandgap-narrowing effect in the heavily doped source and drain.
TL;DR: In this article, the energy band diagram of n-SnO2/n-Si HJ was constructed and the experimental data of the conduction band offset ΔEc and valence band offset ε = 0.55 eV and ΔEv = 1.8 eV were compared with theoretical values.
Abstract: Near-ideal n-SnO2/n-Si heterojunction band edge lineup has been investigated with aid of I–V and C–V measurements. The heterojunction was manufactured by rapid thermal oxidation of Sn metal films prepared by thermal evaporation technique on monocrystalline n-type silicon. The experimental data of the conduction band offset ΔEc and valence band offset ΔEc were compared with theoretical values. The band offset ΔEc = 0.55 eV and ΔEv = 1.8 eV obtained at 300 K. The energy band diagram of n-SnO2/n-Si HJ was constructed. C–V measurements depict that the junction was an abrupt type and the built-in voltage was determined from 1/C2–V plot.
TL;DR: In this article, a pure ultraviolet (UV) light emitting diodes (LEDs) using n-ZnO nanowires as an active layer were fabricated with an insulating MgO dielectric layer as a carrier control layer, where all depositions were continuously performed by metalorganic chemical vapor deposition.
Abstract: Pure ultraviolet (UV) light emitting diodes (LEDs) using n-ZnO nanowires as an active layer were fabricated with an insulating MgO dielectric layer as a carrier control layer, where all depositions were continuously performed by metalorganic chemical vapor deposition. The current-voltage curve of the LEDs showed obvious rectifying characteristics, with a threshold voltage of about 7 V in the sample with 4 nm i-MgO. Under the forward bias of the samples with proper MgO thickness, a sharp UV electroluminescence, located at around 380 nm, was emitted from the active ZnO nanowires, while weak visible emission of around 450–700 nm were observed. The pure UV emission from the ZnO nanowires in the n-ZnO/i-MgO/p + -Si heterostructures was attributed to the electron accumulation in the ZnO by asymmetric band offset and preemptive hole tunneling from Si to ZnO by i-MgO.
TL;DR: In this article, a Ga2O3/6H-SiC heterojunction was studied using synchrotron radiation photoelectron spectroscopy, and the energy band diagram was obtained by analyzing the binding energies of Ga 3d and Si 2p at the surface and the interface of the heterjunction.
Abstract: A high-quality Ga2O3 thin film is deposited on an SiC substrate to form a heterojunction structure. The band alignment of the Ga2O3/6H-SiC heterojunction is studied by using synchrotron radiation photoelectron spectroscopy. The energy band diagram of the Ga2O3/6H-SiC heterojunction is obtained by analysing the binding energies of Ga 3d and Si 2p at the surface and the interface of the heterojunction. The valence band offset is experimentally determined to be 2.8 eV and the conduction band offset is calculated to be 0.89 eV, which indicate a type-II band alignment. This provides useful guidance for the application of Ga2O3/6H-SiC electronic devices.
TL;DR: In this paper, the SiC/SiOx hetero-superlattice with near-stoichiometric SiC as barrier layer for electrical transport and silicon rich SiOx as matrix layer for the quantum dot formation was introduced.
TL;DR: In this paper, the binding energies of core levels and valence band maximum values have been found to be 0.7 ± 0.1 and 0.9µ± 0.1µeV for polar and non-polar GaN/ZnO heterojunctions, respectively.
Abstract: C-plane (polar) and m-plane (nonpolar) GaN/ZnO heterostructures have been fabricated by pulsed laser deposition at room temperature, and their electronic structures have been characterized by synchrotron radiation photoemission spectroscopy. Based on the binding energies of core levels and valence band maximum values, the valence band offsets have been found to be 0.7 ± 0.1 and 0.9 ± 0.1 eV for polar and nonpolar GaN/ZnO heterojunctions, respectively. Both heterostructures show type-II band configurations with conduction band offsets of 0.8 ± 0.1 and 1.0 ± 0.1 eV, respectively. GaN and ZnO show upward and downward band bending toward the interface in the nonpolar GaN/ZnO heterojunction. However, both GaN and ZnO show upward band bending toward the interface in the polar heterojunction, which is attributed to negative charges. Analysis of N 1s spectra has revealed that N–O bonds exist only at the polar interface, which probably caused the formation of the negative charges.
TL;DR: In this paper, the authors measured the energy discontinuity in the GaN/diamond heterostructure and determined the valence band offset (VBO) was 0.38 ± 0.15 eV.
TL;DR: In this paper, the intrinsic ZnO (i-ZnO) film deposited by a vapor cooling condensation system was used as the gate dielectric layer of the AlGaN/GaN MOS-HEMTs.
Abstract: The intrinsic ZnO (i-ZnO) film deposited by a vapor cooling condensation system was used as the gate dielectric layer of the AlGaN/GaN MOS-HEMTs. The chlorine surface treatment was utilized to obtain a high-quality i-ZnO/AlGaN interface due to the reduced surface state density. The chlorine-treated MOS-HEMTs showed the better direct current and pulsed output performances than those of the untreated MOS-HEMTs. The resulting unit gain cutoff frequency and the maximum frequency of oscillation were 9.5 and 19.4 GHz, respectively. The Hooge's coefficient was 7.23 × 10-6, when the chlorine-treated ZnO-gate MOS-HEMTs operated at 100 Hz and the gate-source voltage of -4 V. Compared with the untreated MOS-HEMTs, the chlorine-treated MOS-HEMTs revealed better performances. The valence-band offset of i-ZnO/AlGaN was measured by X-ray photoelectron spectroscopy. The valence-band offset of the i-ZnO film on the untreated and the chlorine-treated AlGaN was 1.53 and 2.05 eV, respectively. The conduction-band offset of the i-ZnO film on the untreated AlGaN and the chlorine-treated AlGaN was deduced to be 0.77 and 1.29 eV, respectively. The improved performances of the chlorine-treated MOS-HEMTs and the enhanced conduction-band offset of the i-ZnO/AlGaN interface were attributed to the decrease of Ga dangling bonds and the passivation of N vacancies on the AlGaN surface by using the chlorine surface treatment.
TL;DR: A model equivalent circuit, combining thermionic emission and space-charge-limited current effects, is proposed which describes the behavior of the heterojunction very well and determines the alignment of the energy bands of 6H-SiC relative to the HOMO and LUMO of P3HT.
Abstract: The exact band alignment at organic/inorganic semiconductor heterojunctions is influenced by a variety of properties and is difficult to predict. For organic/inorganic bilayer heterojunctions made of poly(3-hexylthiophene) (P3HT) and n-type 6H-SiC, the band alignment is determined via current–voltage measurements. For this purpose, a model equivalent circuit, combining thermionic emission and space-charge-limited current effects, is proposed which describes the behavior of the heterojunction very well. From the fitting parameters, an interface barrier height of 1.1 eV between the lowest unoccupied molecular orbital (LUMO) of P3HT and the conduction band (CB) of 6H-SiC is determined. In addition, from the maximum open circuit voltage of 6H-SiC/P3HT diodes, a difference of 0.9 eV between the highest occupied molecular orbital (HOMO) of P3HT and the CB of 6H-SiC is deduced. These two values determine the alignment of the energy bands of 6H-SiC relative to the HOMO and LUMO of P3HT. The 6H-SiC/P3HT bilayer he...
TL;DR: In this article, the authors determined the band offsets in InN/p-Si heterojunctions by high-resolution x-ray photoemission spectroscopy, finding that the valence band of InN is 1.39 eV below that of Si.
Abstract: The band offsets in InN/p-Si heterojunctions are determined by high resolution x-ray photoemission spectroscopy. The valence band of InN is found to be 1.39 eV below that of Si. Given the bandgap of 0.7 eV for InN, a type-III heterojunction with a conduction band offset of 1.81 eV was found. Agreement between the simulated and experimental data obtained from the heterojunction spectra was found to be excellent, establishing that the method of determination was accurate. The charge neutrality level (CNL) model provided a reasonable description of the band alignment of the InN/p-Si interface and a change in the interface dipole by 0.06 eV was observed for InN/p-Si interface.
TL;DR: In this paper, a double line of carbon atoms was added at the interface of a single layer of boronitrene to introduce a line of dipoles at the interfaces.
Abstract: Using density functional methods within the generalized gradient approximation implemented in the Quantum Espresso codes, we modify the band offset in a single layer of boronitrene by substituting a double line of carbon atoms. This effectively introduces a line of dipoles at the interface. We considered various junctions of this system within the zigzag and armchair orientations. Our results show that the ``zigzag-short'' structure is energetically most stable, with a formation energy of 0.502 eV and with a band offset of 1.51 eV. The ``zigzag-long'' structure has a band offset of 1.99 eV. The armchair structures are nonpolar, while the zigzag-single structures show a charge accumulation for the C-substituted B and charge depletion for the C-substituted N at the junction. Consequently there is no shifting of the bands.
TL;DR: Conductive-probe atomic force microscopy (CP-AFM) measurements reveal the existence of a conductive channel at the interface between p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) as well as in good agreement with planar conductance measurements that show a large interface conductance.
Abstract: Conductive-probe atomic force microscopy (CP-AFM) measurements reveal the existence of a conductive channel at the interface between p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) as well as at the interface between n-type a-Si:H and p-type c-Si. This is in good agreement with planar conductance measurements that show a large interface conductance. It is demonstrated that these features are related to the existence of a strong inversion layer of holes at the c-Si surface of (p) a-Si:H/(n) c-Si structures, and to a strong inversion layer of electrons at the c-Si surface of (n) a-Si:H/(p) c-Si heterojunctions. These are intimately related to the band offsets, which allows us to determine these parameters with good precision.
TL;DR: In this paper, the effect of Al and La incorporation on the electronic properties of the interface in the SiO{}_{2}$/HfO${}_{ 2}$ high-k gate stacks was examined using density functional theory.
Abstract: Using density functional theory (DFT) we examine the effect of Al and La incorporation on the electronic properties of the interface in the SiO${}_{2}$/HfO${}_{2}$ high-k gate stacks recently introduced into the advanced modern field effect transistors (FETs). We show that La and Al doping have opposite effects on the band alignment at the SiO${}_{2}$/HfO${}_{2}$ interface: while the Al ions, which substitute preferentially for Si in the SiO${}_{2}$ layer, promote higher effective work function (EWF) values, the substitution of La for Hf decreases EWF. The analysis of the electronic structure of the doped interface suggests a simple relation between the electronegativity of the doping metal, screening properties of the interfacial layer, and the band offset, which allows predicting qualitatively the effect of the high-k gate stack doping with a variety of metals on its EWF.
TL;DR: In this article, an overview of the internal photoemission (IPE) and the significance of this technique when combined with spectroscopic ellipsometry (SE) to investigate the interfacial electronic properties of heterostructures.
TL;DR: In this article, first-principles calculations were performed to investigate the band offsets of (9,0) and (10,0)-BN/C heterostructured nanotubes with different interfaces.
Abstract: We perform first-principles calculations to investigate the band offsets of (9,0) and (10,0) BN/C heterostructured nanotubes with different interfaces. We show that the built-in electric field induced by charge redistribution modulates the band offsets of these nanotubes in different ways. Remarkably enhanced field-emission properties of the heterostructures are also predicted.
28 Jan 2011
TL;DR: In this paper, the atomic and electronic structures of semiconductor interfaces are explained, focusing on fundamental physics revealed by recent researches, and the origins of the Schottky barrier and the band offset are explained.
Abstract: Atomic and electronic structures of semiconductor interfaces are explained, focusing on fundamental physics revealed by recent researches. To understand atomic structures, it is essential to understand how the interface is formed and how stable the interface is. We consider these by illustrating the epitaxial growth and oxidation processes and explaining key concepts such as the growth diagram, growth modes, stress release, and defect generation. On the other hand, the most important quantities to characterize the interface electronic structures are the Schottky barrier and the band offset, because they govern most transport and optical properties around interfaces. The origins of these quantities are explained, using key concepts such as the interface states, charge neutrality level, band bending, and Fermi-level pinning. Prospects for future trend of interface investigations are also illustrated.