Showing papers on "Band offset published in 1994"
TL;DR: In this article, it was shown that the characteristics of light-emitting diodes based upon MEH-PPV are determined by tunneling both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes.
Abstract: In this paper it is demonstrated that the characteristics of light‐emitting diodes based upon MEH‐PPV [more fully known as poly(2‐methoxy,5‐(2’‐ethyl‐hexoxy)‐1,4‐phenylene‐ vinylene)] are determined by tunneling of both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes. It is shown that manipulating these offsets can control the useful operating voltage of the device as well as its efficiency. A model is developed that clearly explains the device characteristics of a wide range of diodes based upon MEH‐PPV. The turn‐on voltage for an ideal device is shown to be equal to the band gap, i.e., 2.1 eV for MEH‐PPV, and is slightly lower at 1.8 eV for an indium‐tin oxide/MEH‐PPV/Ca device. If there is a significant difference in the barrier height, the smaller of the two barriers controls the I–V characteristics, while the larger barrier determines the device efficiency. In indium‐tin‐oxide/MEH‐PPV/Ca devices, the barrier to hole injection is ...
1,435 citations
TL;DR: The band offset increases with decreasing ionicity of the constituent semiconductor material, i.e., the magnitude of the band offset is determined by the competition between ionicity and covalency.
Abstract: The band structures of various semiconductors in both wurtzite (WZ) and zinc-blende (ZB) structures are calculated using the first-principles pseudopotential method within the local-density approximation, and then the band offsets at (111) WZ/ZB interfaces are evaluated for the band-edge states around fundamental gaps. We found that the band offsets are larger for ``zone-boundary states'' having large wave numbers perpendicular to [111] than for ``zone-center states'' having small wave numbers perpendicular to [111]. These phenomena occur because the former offsets are caused by the phase matching of a wave function through the first-nearest-neighboring site, whereas the latter are caused by the difference between the position of the third-nearest-neighboring site in the WZ and ZB structures. In addition, we show that the band offset increases with decreasing ionicity of the constituent semiconductor material, i.e., the magnitude of the band offset is determined by the competition between ionicity and covalency.
367 citations
TL;DR: In this paper, the Harrison model was used to describe the band lineups of InGaAlAs on (001) InP as well as InGaAsP on (1, 2)-InP system with strain effects.
Abstract: We describe the band lineups of InGaAlAs on (001) InP as well as InGaAsP on (001) InP system with strain effects, based on the Harrison model. We show that the compressive strain does not affect the band position so much, and tensile strain raises the band position in the InGaAsP system. It is also shown that both compressive and tensile strains raise the band positions in the InGaAlAs system. The conduction and valence band positions of InGaAs, InGaAsP, and InGaAlAs relative to InP valence band are given in approximate formulas as a function of the strain. We calculate the energy versus in-plane wave vector relationship of the InGaAsP/InGaAs(P) InGaAlAs/InGa(Al)As on InP strained quantum-well systems. We obtain the in-plane effective mass of the strained quantum-well system by fitting the dispersion relationship to a parabolic curve. The in-plane effective masses of several kinds of strained quantum-well systems are listed. >
115 citations
TL;DR: In this paper, the acceptor level of iron in AlN polycrystalline material was found at EV+3.0 eV and the corresponding value for iron in GaN is EV+2.5 eV.
Abstract: A characteristic infrared luminescence spectrum, dominated by a zero‐phonon line at 1.30 eV, has been observed on AlN polycrystalline material. It is assigned to the spin‐forbidden internal 3d–3d transition 4T1(G)→6A1(S) of Fe3+Al(3d5). By photoluminescence excitation spectroscopy the (‐/0) acceptor level of iron in AlN could be located at EV+3.0 eV. The corresponding value for iron in GaN is EV+2.5 eV. From these values, the valence‐band offset in AlN/GaN heterojunctions is predicted as ΔEV=0.5 eV, the conduction‐band offset as ΔEC=2.3 eV.
105 citations
TL;DR: In this article, the authors described the method of cross-sectional scanning tunnelling microscopy (STM) for the observation of structural features on an atomic scale, including alloy clustering, interface roughness, band offsets, quantum subbands and point defects.
Abstract: The method of cross-sectional scanning tunnelling microscopy (STM) is described. Illustrative examples are given of studies of III-V semiconductor systems, including AlxGa1-xAs/GaAs superlattices, InAs/GaSb superlattices and low-temperature-grown GaAs. Physical properties studied include alloy clustering, interface roughness, band offsets, quantum subbands and point defects. In each case, STM permits the observation of structural features on an atomic scale. The associated electronic spectroscopy for states a few eV on either side of the Fermi level can be determined. Such information is relevant for the operation of devices constructed from these layered semiconductor systems.
61 citations
TL;DR: In this paper, a comparative study of two different spectroscopic techniques in order to determine the valence band offset in CdTe/Cd1−xMnxTe quantum wells is presented.
Abstract: We present a comparative study of two different spectroscopic techniques in order to determine the valence band offset in CdTe/Cd1−xMnxTe quantum wells. The energy difference between heavy‐ and light‐hole excitons as a function of the heavy‐hole transition energy is known as a sensitive tool for the determination of the valence band potential height. In the present study we have employed this technique to CdTe/Cd1−xMnxTe quantum wells. A valence band offset around Qv=0.30 is determined, which is found to be valid in the whole range of investigated Mn contents up to x=0.27. In semimagnetic quantum wells the tuning of potential heights in external magnetic fields offers the possibility to evaluate the valence band offset. This technique has been widely employed to CdTe/Cd1−xMnxTe, but no consensus has been reached yet. We have analyzed the Zeeman splitting of the heavy‐hole exciton in CdTe/Cd1−xMnxTe quantum wells with different Mn contents. Using the valence band offset as an adjustable parameter, a smalle...
43 citations
29 citations
TL;DR: In this paper, a p-type δ-doped sheet was used to cancel the band bending near the Schottky interface, enabling a direct measurement of the conduction band offset at room temperature.
Abstract: Ballistic electron emission microscopy (BEEM) has been used to study electron transport across single barrier AlxGa1−xAs/GaAs heterostructures. The structures, grown by molecular beam epitaxy, utilized a p‐type δ‐doped sheet to cancel the band bending near the Schottky interface, enabling a direct measurement of the conduction band offset at room temperature. The band offset at room temperature for x=0.21 is 0.19 eV and for x=0.42 is 0.33 eV. Measurements at 77 K gave values of 0.20 eV for x=0.21 and 0.35 eV for x=0.42. These results demonstrate that BEEM can be used to probe the transport properties of semiconductor heterostructures which are spatially beneath the Schottky barrier.
24 citations
TL;DR: In this paper, experimental photoresponses and electrical properties of metal/ beta-FeSi2/Si structures are presented. And the authors compare three kinds of samples: two with a thin epitaxial silicide layer (180 AA), prepared by two different methods, and one with a thick polycrystalline silicide layers (2500 AA).
Abstract: Experimental photoresponses and electrical characteristics of metal/ beta -FeSi2/Si structures are presented. Three kinds of samples are compared: two with a thin epitaxial silicide layer (180 AA), prepared by two different methods, and one with a thick polycrystalline silicide layer (2500 AA). The rectifying behaviour and the photoelectric response of the three kinds of samples are different. In the thin samples these properties are governed by those of the beta -FeSi2/Si interface, whereas for thick samples bulk mechanisms dominate. Analysis of the photocurrent in one kind of thin sample shows that two contributions exist. Their intensities follow similar temperature behaviours but the two transition thresholds do not. These considerations allow assignment of the initial and final states of the transitions, and the upper threshold is shown to correspond to an internal photoemission effect at the beta -FeSi2/Si interface. The conduction band offset is deduced from the difference between the two thresholds. The valence band discontinuity is less than 50 meV between 360 K and 260 K, whereas it changes sign when the temperature decreases below 260 K, the two bandgaps becoming nested within each other. These properties are also discussed for the other kinds of sample and related to the mechanisms which are responsible for the electrical characteristics.
24 citations
TL;DR: In this paper, the splitting between the lowest energy heavy and light hole excitonic transitions is observed to be only weakly dependent on well width over the range 25-300 A, for sample sets with x = 0.56 and x=0.59.
Abstract: (AlGaIn)P‐on‐GaAs structures incorporating compressively strained Ga1−xInxP (x≳0.48) quantum well active layers have been studied by low‐temperature photoluminescence excitation spectroscopy. The splitting between the lowest energy heavy‐ and light‐hole excitonic transitions is observed to be only weakly dependent on well width over the range 25–300 A, for sample sets with x=0.56 and x=0.59. Envelope function approximation fitting, based on bulk valence band dispersion calculations which include the strain‐induced interaction with the spin split‐off band, shows this splitting behavior to be a sensitive function of the heterojunction band offset. Conduction band discontinuities, ΔEc, of 0.67ΔEg (x=0.56) and 0.85ΔEg (x=0.59) provide the best fit to these and all higher lying transitions for the full range of structures examined, indicating that poor hole confinement is a limiting factor in practical compressive strain (AlGaIn)P laser device performance.
18 citations
TL;DR: In this paper, the authors show that II-VI/CuInSe 2 heterojunctions have significant band offsets which challenge the traditional explanation of device operation, and that these large valence band offsets demonstrate the failure of the common anion rule.
05 Dec 1994
TL;DR: In this paper, a pseudomorphic GaAsSb layer was employed to obtain a band alignment at a InGaAs or InAlAs p-n junction favorable for forward bias tunneling.
Abstract: We report a new approach to tunnel junctions that employs a pseudomorphic GaAsSb layer to obtain a band alignment at a InGaAs or InAlAs p-n junction favorable for forward bias tunneling. Since the majority of the band offset between GaAsSb and InGaAs or InAlAs is in the valence band, when an GaAsSb layer is placed at an InGaAs or InAlAs p-n junction the tunneling distance is reduced and the tunneling current is increased. For all doping levels studied, the presence of the GaAsSb-layer enhanced the forward tunneling characteristics. In fact, in a InGaAs/GaAsSb tunnel diode with p=1.5/spl times/10/sup 18/ cm/sup -3/ a peak tunneling current sufficient for a 1000 sun InP/InGaAs tandem solar cell interconnect was achieved while a similarly doped all-InGaAs diode was rectifying. This approach affords a new degree of freedom in designing tunnel junctions for tandem solar cell interconnects. Previously only doping levels could be varied to control the tunneling properties. Our approach relaxes the doping requirements by employing a GaAsSb-based heterojunction.
TL;DR: In this article, isotype heterojunctions of n-InAsSb/N-GaSb were grown by liquid phase epitaxy from Sb-solution.
Abstract: Isotype heterojunctions of n-InAsSb/N-GaSb were grown by liquid phase epitaxy from Sb-solution. The current-voltage and capacitance-voltage characteristics of these structures were investigated. Valence band and conduction band offsets were measured to be AEv = 0.40 eV and AEc = 0.84 eV, respectively, in good agreement with theory. Electroluminescence emission at 4 am from these isotype heterojunction diodes is reported for the first time. The injection mechanisms determining luminescence efficiency are also briefly discussed.
TL;DR: In this article, temperature-dependent current-voltage measurement was employed to study the band offsets of the In0.30Ga0.70As/In0.29Al0.71As heterojunction.
Abstract: Temperature-dependent current-voltage measurement was employed to study the band offsets of the In0.30Ga0.70As/In0.29Al0.71As heterojunction. The conduction band discontinuity was determined to be 0.71 ± 0.05 eV which corresponds to a conduction band offset to bandgap difference ratio of ~0.66. The comparison between experimental and theoretical results is presented.
TL;DR: In this article, band offsets and electronic structures of various II-VI strained superlattices are calculated by the first-principles pseudopotential method in the local density approximation.
Abstract: Band offsets and electronic structures of various II–VI strained superlattices are calculated by the first-principles pseudopotential method in the local density approximation. The differences of band structures under strain between wurtzite and zinc-blende crystal structures are first analyzed. The deformation potentials are calculated for all II–VI compounds. However the strain in II–VI superlattices is so large that nonlinear variation of energy levels with changing the magnitude of strain appears. There is a chemical trend of offset that energy levels of the heavy-hole and the electron states increase as the atomic number of anion and cation atoms increases, respectively. The calculated band offsets drastically vary with changing strain surroundings. The practical usage of the present results is illustrated.
TL;DR: In this article, a tensile-strained GaAsP barrier was used to allow light and heavy-hole valence bands to be approximately merged within a wide range of well widths and strains, thereby increasing the yield of devices requiring these characteristics.
Abstract: An investigation of GaAs QW's with tensile-strained GaAsP barriers grown on GaAs substrates by organometallic vapor phase epitaxy is reported. We demonstrate that this system permits light- and heavy-hole valence bands to be approximately merged within a wide range of well widths and strains, thereby increasing the yield of devices requiring these characteristics. A few series of quantum wells with three phosphorus compositions (6%, 9%, and 19%) were grown and studied by photoluminescence and polarized photoluminescence excitation spectroscopy. We compared our experimentally determined conduction band to heavy-hole and light-hole transition energies with finite potential well calculations utilizing a previously developed strain dependent band offset model. We obtained excellent agreement between experimental and calculated results without any adjustment or fitting of parameters. >
TL;DR: In this paper, a single-heterostructure of CuGaSe2/CuAlSe2 chalcopyrite semiconductors was successfully grown epitaxially on a GaAs(001) substrate using a low-pressure metal organic chemical vapor deposition technique.
Abstract: A single-heterostructure of CuGaSe2/CuAlSe2 chalcopyrite semiconductors was successfully grown epitaxially on a GaAs(001) substrate using a low-pressure metal organic chemical vapor deposition technique. The valence-band discontinuity for the CuGaSe2/CuAlSe2 heterointerface was estimated to be 0.8±0.1 eV by means of X-ray photoelectron spectroscopy. The CuGaSe2/CuAlSe2 structure was found to have the straddling-type heterointerface, and the band discontinuity was found to be distributed mainly in the valence band.
TL;DR: In this article, the energy distribution of the steps has been analyzed using models of Tipe-I and Tipe II superlattices, and the theoretical results have been shown to follow the theoretical values of the energy steps for TipeII super lattices.
TL;DR: Magneto-optical experiments have been used to study a range of InoaAsP-based multiple-quantumwell structures containing biaxial strains, providing details of the valence-band nonparabolicities, and electronlike behavior is demonstrated for both heavy and light holes with different amounts of tensile strain.
Abstract: Magneto-optical experiments have been used to study a range of InoaAsP-based multiple-quantumwell (MQW) structures containing biaxial strains, ranging from 1.6% tensile to 1.0% compressive. The observed excitonic transitions, involving both heavy and light holes, are studied in fields up to 15 T. Estimates of the hole effective masses are made, providing details of the valence-band nonparabolicities, and electronlike behavior is demonstrated for both heavy and light holes with different amounts of tensile strain. This is related to band crossings within the valence band and enables an estimate of 0.68+0. 10 to be made of the heterojunction band offset in a strained In, „Ga„AsilnGaAsP MQW, with approximately 1.25%%uo tensile strain in the well region. The experimental data are compared to the results of k. p Hamiltonian calculations of the in-plane valence-band dispersion.
TL;DR: In this article, the authors used X-ray photoelectron spectroscopy to measure the valence band offset for the MgSe/Cd 0.54 Zn 0.46 Se heterojunction grown by molecular beam epitaxy.
TL;DR: In this paper, the authors investigated the well exciton features in ZnSe/ZnMnSe quantum structures grown by molecular beam epitaxy (MBE) using various spectroscopic techniques.
TL;DR: In this paper, the authors used time-resolved transmission and photocurrent measurements at 1.06 µm to study carrier sweepout in strain-relaxed InGaAs/GaAs and strain-balanced InGaA/GaAP quantum well modulators.
Abstract: We have used time‐resolved transmission and photocurrent measurements at 1.06 μm to study carrier sweepout in strain‐relaxed InGaAs/GaAs and strain‐balanced InGaAs/GaAsP quantum well modulators. Our results show carrier sweepout on a picosecond time scale from both structures, in agreement with the high saturation intensities measured for these devices. Carrier escape from the InGaAs/GaAs structure is facilitated by a low band offset and occurs in tens of picoseconds even without external bias. In the InGaAs/GaAsP structure, which has a much larger band offset, resonant tunneling reduces the sweepout time from 1.8 ns at zero bias to 10 ps at −6 V.
TL;DR: In this article, single and multiple quantum well structures were studied by luminescence and reflection spectroscopy in a magnetic field up to 7.5 T. Using the strain-induced heavy and light hole splitting of the barrier and well excitons, the valence band offset was determined in the framework of a Kronig-Penney model calculation.
TL;DR: In this paper, the band offsets of Mg-mixed ZnSSe strained superlattices are calculated by the first-principles pseudopotential method in the local density approximation.
Abstract: The band offsets of Mg-mixed ZnSSe strained superlattices are calculated by the first-principles pseudopotential method in the local density approximation. It is shown that Mg-mixing into the barrier layers increases the band offsets for both the heavy-hole and electron states, thus strengthening the carrier confinement, which is in agreement with experiments. A chemical trend of the offset among various II-VI superlattices is discussed using the atomic orbital energies and radii.
TL;DR: In this article, weak field Hall effect measurements between 34 and 300 K were applied to three PbSe/PbEuSe (E g [Pb euSe] = 440 meV at 300 K) MQW samples on KCl.
Abstract: Weak field Hall effect measurements between 34 and 300 K were applied to three PbSe/PbEuSe ( E g [PbEuSe] = 440 meV at 300 K) MQW samples on KCl. By calculating the quasi-Fermi energy levels the temperature dependent band-edge offsets were determined. The valence band offset ΔE rmv was found to be 65 meV at 34 K with a positive temperature coefficient of 0.68 meV/K. Thus ΔE v = 43 + 0.68 T (meV) is suggested.
TL;DR: In this paper, the first demonstration of ZnSe/Ge/GaAs and InGaAs/GaA closely lattice-matched heterojunction bipolar transistors (HBTs) grown by the low-pressure metal-organic chemical vapor deposition (MOCVD) system was reported.
Abstract: We report the first demonstration of ZnSe/Ge/GaAs and ZnSe/InGaAs/GaAs closely lattice-matched heterojunction bipolar transistors (HBTs) grown by the low-pressure metal-organic chemical vapor deposition (MOCVD) system. Both ZnSe/Ge/GaAs and ZnSe/lnGaAs/GaAs HBTs have advantages of larger valence band offset (ΔE v), lower base resistance, and lower contact resistance compared with the AlGaAs/GaAs HBT for high-speed digital circuits. Based on S-parameter measurements at 77 K, a unity-gain cutoff frequency f T=6 GHz and a maximum oscillation frequency f max=13 GHz at a collector current density of 1.8 kA/cm2 were obtained for the ZnSe/Ge/GaAs HBT. To our knowledge, this is the first II-VI/IV/III-V compound-semiconductor HBT ever reported to operate at such a high frequency.
TL;DR: In this article, the authors compared the model theories used to obtain the discontinuity in the valence-band edge at the interface between two semiconductors compared with results from first-principles supercell calculations.
Abstract: Calculated electronic properties of compound semiconductor hetero structures are presented and compared with experimental results. Model theories used to obtain the discontinuity in the valence-band edge at the interface between two semiconductors are compared with results from first-principles supercell calculations. The so-called ‘dielectric midgap energy’ model yields good estimates of the band offsets in junctions where interface states have little influence on the charge transfer. These cases are simultaneously those where the transitivity rule applies. Lattice matched cases as well as systems with built-in strain are discussed. Strain effects are included in lattice mismatched systems, and also externally applied pressures can be taken into account. As an example of the latter we examine the type I-II conversion in ZnS/ZnSe superlattices under pressure. Superlattice band structures are derived within the density-functional theory, local approximation. The valence bands are well described, b...
TL;DR: In this article, high-density excitation spectroscopy using a high-resolution pulsed excimer-dye laser system as well as a picosecond titanium-sapphire laser for time-resolved measurements was used to investigate nonlinear and stimulated emission of ZnSxSe1 − x/ZnSe multilayer structures.
Abstract: Non-linear and stimulated emission of ZnSxSe1 − x/ZnSe multilayer structures grown by MOVPE on GaAs is investigated by means of high-density excitation spectroscopy using a high-resolution pulsed excimer-dye laser system as well as a picosecond titanium–sapphire laser for time-resolved measurements. Heterostructures with ZnSe layers or single and multiple quantum wells were grown in which the ZnSe layer widths were varied between 1 nm (strong quantum confinement) and 500 nm (quasi-bulk situation). The sulphur concentration in the ZnSxSe1 − x buffer, barrier and cap layers was chosen between x = 0.045 and x = 0.74 in order to find the most promising compromise with regard to maximum band offset to ZnSe for most efficient carrier confinement and suitable waveguiding properties depending on variation in the refractive index, and to highest structural quality of the actively emitting ZnSe layers. Stimulated emission is found to occur in all samples, being brightest in the sample with the lowest sulphur concentration in the cap and barrier layers. Its dynamical properties point to a probable interpretation in terms of electron–hole plasma creation, which, however, may not be the basic process in narrow-quantum wells or strongly structurally disturbed samples.
TL;DR: In this article, the authors show that the critical energy of the total transmission electron wave can be either in the conduction band or valence band, depending on whether the valence-band offset is larger than conductionband offset.
TL;DR: In this paper, a direct comparison of admittance spectroscopy and DLTS on p -Si/Si 1−x Ge x /Si quantum well (QW) structures with x = 0.17 using n + p mesa diodes with buried QW layer is presented.
Abstract: Results are presented concerning direct comparison of admittance spectroscopy and DLTS on p -Si/Si 1− x Ge x /Si quantum well (QW) structures with x = 0.17 using n + p mesa diodes with buried QW layer. The temperature dependence of potential barriers at the QW and of the Fermi level determine the activation energy E a of the conductance across the QW. From E a a band offset of ΔE v = 0.16 eV was estimated. DLTS data suggest that hole emission from QW was observed with activation energy in correspondence with ΔE v .