Showing papers on "Band offset published in 1995"
TL;DR: In this article, a bilayer bilayer quantum well (BQW) was realized, which consists of two adjacent pseudomorphic layers of GaAs1−xSbx and InyGa1−yAs sandwiched between GaAs barriers.
Abstract: We have realized a (GaAs1−xSbx‐InyGa 1−yAs)/GaAs bilayer‐quantum well (BQW), which consists of two adjacent pseudomorphic layers of GaAs1−xSbx and InyGa1−yAs sandwiched between GaAs barriers. Photoluminescence was observed at longer wavelengths than those found for corresponding InyGa1−yAs/GaAs and GaAs1−xSbx/GaAs single quantum wells (SQW), which indicates a type‐II band alignment in the BQW. The longest 300 K emission wavelength achieved so far was 1.332 μm. For an accurate determination of the band offset between GaAs1−xSbx and GaAs, required for a theoretical modeling of the interband transition energies of these BQWs, a large set of GaAs1−xSbx /GaAs SQWs was prepared from which a type‐II band alignment was deduced, with the valence band discontinuity ratio Qv found to depend on the Sb concentration x (Qv=1.76+1.34 x). With this parameter it was possible to calculate the expected interband transition energies in a BQW structure without any adjustable parameters. The calculations are in agreement with ...
81 citations
TL;DR: In this article, band offsets at CdS/CuInS2 heterojunctions were studied by x-ray photo-emission spectroscopy and it was shown that the cyanide treatment improves the interface to give rise to the alignment of the conduction band minima, which is suitable to the solar cell applications.
Abstract: Band offsets at CdS/CuInS2 heterojunctions are studied by x‐ray photoemission spectroscopy. At the CdS/cyanide‐treated CuInS2 junction, the conduction band offset is as small as −0.05±0.15 eV, while the valence band offset is 1.18±0.10 eV. The CdS/Cu‐rich CuInS2 heterojunction without the treatment, however, possesses a conduction band offset of ∼−0.7 eV. This result suggests that the cyanide treatment improves the interface to give rise to the alignment of the conduction band minima, which is suitable to the solar cell applications.
59 citations
TL;DR: In this paper, a heteroquantum-dots (HQD) model for hydrogenated nanocrystalline silicon films (nc•Si:H) is proposed, where the activated electrons in the quantum dots conduct via quantum tunneling through the interface barriers.
Abstract: A heteroquantum‐dots (HQD) model for hydrogenated nanocrystalline silicon films (nc‐Si:H) is proposed. The main features of our model are as follows. (i) the nanocrystalline grains and the amorphous counterparts in which they are embedded have very different band gap and band structures. As a result, they form heterojunctionlike structures in the interface regions, where the band offset effects dramatically reduce the activation energy and the grains act like quantum dots. (ii) In the presence of an external field, the activated electrons in the quantum dots conduct via quantum tunneling through the interface barriers. By means of the HQD model, we have identified the conduction of nc‐Si:H as a thermal‐assisted tunneling process. Our results show that there are two distinct regimes for the conductivity of nc‐Si:H: (i) the low‐temperature regime, where there is a simple activation energy ΔE; (ii) the high‐temperature regime, where ΔE is effectively enhanced by the temperature effect of the electronic tunne...
53 citations
TL;DR: In this paper, a theoretical study of InGaAsP-InGaAsp multiple quantum-well lasers emitting at 1.55 /spl mu/m has been carried out to investigate the variation of threshold current density and differential gain with strain, well width and well number.
Abstract: A theoretical study of InGaAsP-InGaAsP multiple quantum-well lasers emitting at 1.55 /spl mu/m has been carried out to investigate the variation of threshold current density and differential gain with strain, well width and well number. We show that the greatest scope for exploiting this quaternary alloy in laser structures is through the use of compressive wells with unstrained or tensile barriers. We consider structures with a fixed compressive strain of 1% but variable well width, and also with fixed well width but variable strain from 0% to 1.75%. For structures with 1% compressive wells and unstrained barriers we find that the optimum structure for lowest threshold current density with sizable differential gain consists of six 35-/spl Aring/ quantum wells. We find also that there is little benefit to having compressive strains greater than 1.2%. In addition we examine zero-net-strain (ZNS) structures with compressive wells and tensile barriers. We show how the conduction band offset can be significantly increased and valence band offset reduced in such structures. Our gain calculations suggest that the large modification in band offset can decrease the threshold current density compared to similar devices with unstrained barriers. >
42 citations
TL;DR: Arsenic-rich InAs/lnAs1-xSbx strained layer superlattices (SLSs) were studied for their potential application as infrared emitters as discussed by the authors.
Abstract: Arsenic-rich InAs/lnAs1-xSbx strained layer superlattices (SLSs) grown on GaAs substrates by molecular beam epitaxy (MBE) are studied for their potential application as infrared emitters. The long-wavelength emission (4-11 mu m) is highly sensitive to superlattice design parameters and is accounted for by a large type-II band offset, greater than in previously studied antimony-rich InSb/lnAs1-xSbx SLSs. High internal PL efficiencies (>10%) and intense luminescence emission were observed at these long wavelengths despite large dislocation densities. Initial unoptimized InAs/lnAs1-xSbx SLS light emitting diodes gave approximately=200 nW of lambda =5 mu m emission at 300 K.
41 citations
TL;DR: In this paper, band-edge shifts induced by the electron-phonon interaction are calculated for HgCdTe alloys and various semiconductor compounds starting from accurate zero-temperature band structures.
Abstract: Band-edge shifts induced by the electron-phonon interaction are calculated for HgCdTe alloys and various semiconductor compounds starting from accurate zero-temperature band structures. The calculated temperature variation of gaps agrees with experiments to better than 10% in all materials except InAs and InSb where the deviation is about 50%. While the simple picture that the intra (inter)-band transitions reduce (increase) the gap still holds, we show that both the conduction band edge Ec and valence band edge Ev move down in energy. These shifts in Ev affect the valence band offsets in heterojunctions at finite temperature. The temperature variations of valence band offset and the electron effective mass are also reported.
30 citations
TL;DR: In this article, the authors reported the temperature dependence of Al0.46In0.54As/InP transition energies and the SLL energy curve with respect to the conduction and valence bands.
Abstract: We report the temperature dependence of Al0.46In0.54As photoluminescence (PL) transition energies and Al0.46In0.54As/InP interface staggered line-up luminescence (SLL) energy. The S shape appearing from 4 to 90 K on the energy versus temperature curves of these PL energies is due to extrinsic recombinations. In particular, the S shape of the SLL energy curve versus temperature is probably due to acceptor impurities localized in AlInAs, at the interface (on-edge impurities). The binding energy of on-edge impurities is lower than its value in the bulk material. This explains why the S shape is less pronounced on the SLL than on the AlInAs PL curve. The band offsets were determined by solving the Schrodinger-Poisson equation system with a self-consistent calculation program. At 4.5 K, the conduction and valence band offsets of the Al0.46In0.54As/InP interface were respectively 0.384 eV and 0.295 eV. This is in agreement with the already reported value of 410 meV for the conduction band offset of the lattice-matched Al0.48In0.52As/InP heterostructure. The temperature dependence of the conduction and valence band offsets is shown to be important: respectively 35 meV and 23 meV between 4.5 and 300 K. The Van Vechten-Malloy model (following a thermodynamic approach) for the temperature dependence of the band offsets is compared with our results. The comparison shows only a qualitative agreement.
26 citations
TL;DR: In this paper, the authors measured a valence band offset of 880 meV between ZnSe and ZnTe and observed a transition from a type II to type I line-up in the ZnMgSe-ZnTe system for a Mg concentration of about 60%.
26 citations
TL;DR: In this paper, infrared magneto-optical studies of band gaps and electron cyclotron resonances of a narrow-gap HgTe superlattice were conducted at liquidhelium temperatures.
Abstract: We report here on infrared magneto-optical studies of band gaps and electron cyclotron resonances of a narrow-gap HgTe-${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Te superlattice. The experimental electron effective mass at the conduction-band edge and four different interband transition energies are compared to the prediction of a 8\ifmmode\times\else\texttimes\fi{}8 k\ensuremath{\cdot}p band-structure calculation in order to determine the valence-band discontinuity between HgTe and CdTe. At liquid-helium temperatures an excellent description of the experiment is obtained with a band offset of 550 meV. Agreement between experiment and theory is not satisfactory with the valence-band offset of 350 meV as deduced from x-ray and ultraviolet photoelectron spectroscopy.
24 citations
TL;DR: In this article, the photoluminescence properties of In0.5Ga 0.5P/AlxGa1−xAs heterojunctions in both staggered and straddling band alignment regimes have been investigated.
Abstract: Photoluminescence properties of In0.5Ga0.5P/AlxGa1−xAs heterojunctions in both staggered and straddling band alignment regimes have been investigated. From the relation between the energies of below‐band gap luminescence and Al compositions in the staggered band alignment regime, we determined the Al composition for null conduction band offset of the heterojunction as well as the conduction band offset value of In0.5Ga0.5P/GaAs heterojunction. Assuming the transitivity between the conduction band offset values, we also obtained the fraction of the band gap energy difference that is associated with the conduction band offset of an AlGaAs/GaAs heterojunction.
23 citations
TL;DR: In this article, X-ray photoelectron spectroscopy is used to determine the band offset at the SiC/AIN (0001) interface, where the valence band spectra are determined for bulk materials and analyzed with the help of calculated densities of states.
Abstract: X-ray photoelectron spectroscopy is used to determine the band-offset at the SiC/AIN (0001) interface First, the valence band spectra are determined for bulk materials and analyzed with the help of calculated densities of states Core levels are then measured across the interface for a thin film of 2H-AIN on 6H-SiC and allow us to extract a band offset of 14 ±03 eV The analysis of the discrepancies between measured peak positions and densities of states obtained within the local density approximation provides information on self-energy corrections in good agreement with independent calculations of the latter
TL;DR: In this article, the metalorganic chemical vapor deposition (MOCVD) growth of CdTe on bulk n-type HgCdTe is reported and the resulting interfaces are investigated.
Abstract: The metalorganic chemical vapor deposition (MOCVD) growth of CdTe on bulk n-type HgCdTe is reported and the resulting interfaces are investigated. Metalinsulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage and current-voltage characteristics. The MOCVD CdTe which was developed in this study, exhibits excellent dielectric, insulating, and mechano-chemical properties as well as interface properties, as exhibited by MIS devices where the MOCVD CdTe is the single insulator. Interfaces characterized by slight accumulation and a small or negligible hysteresis, are demonstrated. The passivation properties of CdTe/ HgCdTe heterostructures are predicted by modeling the band diagram of abrupt and graded P-CdTe/n-HgCdTe heterostructures. The analysis includes the effect of valence band offset and interface charges on the surface potentials at abrupt hetero-interface, for typical doping levels of the n-type layers and the MOCVD grown CdTe. In the case of graded heterojunctions, the effect of grading on the band diagram for various doping levels is studied, while taking into consideration a generally accepted valence band offset. The MOCVD CdTe with additional pre and post treatments and anneal form the basis of a photodiode with a new design. The new device architecture is based on a combination of a p-on-n homojunction in a single layer of n-type HgCdTe and the CdTe/HgCdTe heterostructure for passivation.
TL;DR: In this paper, the core level binding energies with respect to the valence-band maximum in both GaN and A1N bulk films were measured by using x-ray photoemission spectroscopy.
Abstract: The valence-band discontinuity at a wurtzite GaN/AIN (0001) heterojunction is measured by means of x-ray photoemission spectroscopy. The method first measures the core level binding energies with respect to the valence-band maximum in both GaN and A1N bulk films. The precise location of the valenceb and maximum is determined by aligning prominent features in the valenceb and spectrum with calculated densities of states. Subsequent measurements of separations between Ga and Al core levels for thin overlayers of GaN film grown on A1N and vice versa yield a valence-band discontinuity of ΔEv = 0.8+- 0.3 eV in the standard Type I heterojunction alignment.
TL;DR: In this article, the authors performed 1-2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminecence studies of ZnSe/GaAs(100) heterostructures grown by molecular beam epitaxy.
Abstract: We performed 1—2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminescence studies of ZnSe/GaAs( 100) heterostructures grown by molecular beam epitaxy. Our goal was to investigate the deep level electronic structure and its connection with the heterojunction band offsets. We observed novel deep level emission features at 0.8, 0.98, 1.14, and 1.3 eV which are characteristic of the ZnSe overlayer and independent in energy of overlayer thickness. The corresponding deep levels lie far below those of the near-bandedge features commonly used to characterize the ZnSe crystal quality. The relative intensity and spatial distribution of the deep level emission was found to be strongly affected by the Zn/Se atomic flux ratio employed during ZnSe growth. The same flux ratio has been shown to influence both the quality of the ZnSe overlayer and the band offset in ZnSe/GaAs heterojunctions. In heterostructures fabricated in Se-rich growth conditions, that minimize the valence band offset and the concentration of Se vacancies, the dominant deep level emission is at 1.3 eV. For heterostructures fabricated in Zn-rich growth conditions, emission by multiple levels at 0.88,0.98, and 1.14 eV dominates. The spectral energies and intensities of deep level transitions reported here provide a characteristic indicator of ZnSe epilayer stoichiometry and near-interface defect densities.
TL;DR: This work evidences the important role of unconfined excited states in optical transitions and explains that low-energy structures observed in the absorption spectra are due to transitions between spatially separated conduction and valence superlattice confined states.
Abstract: We have theoretically studied large-, short-, and very-short-period ZnSe/ZnTe strained superlattices. We use an ${\mathit{sp}}^{3}$${\mathit{s}}^{\mathrm{*}}$ tight-binding model with spin-orbit coupling in order to calculate energies of superlattice electronic states and optical transition probabilities. This enables us to estimate the valence-band offset considering many experimental studies on a large range of samples with various thicknesses and strain states. For large-period superlattices, our work evidences the important role of unconfined excited states in optical transitions and explains that low-energy structures observed in the absorption spectra are due to transitions between spatially separated conduction and valence superlattice confined states. The main absorption contribution at higher energy is explained by strong transitions occurring between valence and unconfined conduction states. These features result from the type-II nature of this superlattice. Our calculation leads to a 1.02\ifmmode\pm\else\textpm\fi{}0.02 eV unstrained band offset, which allows a very good comparison with the studied experimental data.
TL;DR: In this article, the positions of the conduction band Γ and X minima were used to design samples specifically for high pressure experiments in which they have measured the band offsets, and they obtained a value for conduction b-and offset (ΔE c ) of ΔE c = 0.73 ΔE g independent of x.
TL;DR: In this paper, it has been found that the perpendicular conductivity of the lattice matched In0.52Al0.48As/In0.53Ga0.47As structures is controlled by the strong temperature dependence of the space charge region width around the quantum well layer.
Abstract: Results are presented of admittance spectroscopy measurements on the lattice‐matched In0.52Al0.48As/In0.53Ga0.47As single‐quantum‐well structures. It has been found that the perpendicular conductivity of the structure is controlled by the strong temperature dependence of the space‐charge region width around the quantum‐well layer. This process is governed by a high density of deep electron traps present in the layers adjacent to the quantum well. Therefore, the energy activation of perpendicular conductivity is determined by the deep‐level defects rather than the thermionic emission of electrons from the quantum well. Because of this, it is impossible to extract the magnitude of the band offset between the quantum well and barrier layers from the admittance measurements performed in this study.
TL;DR: In this article, the values of band offsets in heterojunctions of In 0.15 Ga 0.85 As y Sb 1−y Al 0.5 ga 0.77 and 1.25 eV, with the valence band offsets of −(0.0−0.02) and −0.15 eV.
Abstract: The values of band offsets in heterojunctions of In 0.15 Ga 0.85 As y Sb 1−y Al 0.5 Ga 0.5 As z Sb 1−z and In 0.85 Ga 0.15 As y Sb 1−y Al 0.5 Ga 0.5 As z Sb 1−z with both quaternaries lattice-matched to GaSb, have been measured by capacitance-voltage studies. The conduction band offsets are, respectively, 0.75–0.77 and 1.25 eV, with the valence band offsets of −(0.0–0.02) and −0.15 eV. It is shown that the transitivity rule is observed and that there is correlation of the valence band offsets with the difference in the Schottky barrier heights of corresponding materials.
TL;DR: In this paper, local density functional calculations for bulk A1N, GaN, and InN in the wurtzite, zincblende, and rocksalt structures are presented.
Abstract: Ab initio local-density-functional calculations are presented for bulk A1N, GaN, and InN in the wurtzite, zincblende, and rocksalt structures. Structural transition pressures and deformation potentials of electronic gaps are investigated. In addition, we study the band offset at the polar (0001) and non-polar (1010) AIN/GaN interfaces. Within AIN-on-GaN epitaxial conditions, we obtain valence-band offset values close to 0.7 eV for both interfaces. From the macroscopic field appearing along the growth direction of the polar interface (tentatively attributed to AIN macroscopic polarization), an estimate of the macroscopic dielectric constant of GaN is extracted. All calculations employed conjugate-gradient total-energy minimizations, ultrasoft pseudopotentials, and plane waves at 25 Ryd cutoff.
TL;DR: In this paper, the bias-dependent quantum efficiency of a HgCdTe P-on-n heterojunction photodiode with a valence band barrier is investigated.
Abstract: A new analytical model for the bias-dependent quantum efficiency of a HgCdTe P-on-n heterojunction photodiode with a valence band barrier elucidates the important physics of the phenomenon and shows that the background-induced shunt resistance is a result of the same mechanism, that is, a tendency of the light-induced carriers to pile up in the base layer due to the retarding field produced by the barrier. A parameterized version of the model agrees well with experimental current-vs-voltage and noise measurements.
TL;DR: In this paper, the authors estimated the valence band discontinuity ΔEV at the p −ZnSe/p −Te interface by means of electrical measurements, and found that ΔEV∼0.8 eV is the smallest value known.
Abstract: We have estimated the valence band discontinuity ΔEV at the p‐ZnSe/p‐ZnTe interface by means of electrical measurements. From capacitance‐voltage measurement of a Schottky‐like barrier at the heterojunction, ΔEV∼0.8 eV is found. The current‐voltage characteristics of the junctions, however, suggest smaller values for ΔEV. The likely origin of this difference is leakage paths of the current in the barrier at the junction.
TL;DR: In this paper, a technique based on photoluminescence excitation measurements is described for direct determination of the band alignment in a quantum well formed from nonmagnetic and semimagnetic materials.
Abstract: A technique based on photoluminescence excitation measurements is described for the direct determination of the band alignment in a quantum well formed from nonmagnetic and semimagnetic materials. Results are presented for a series of CdTe-${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te quantum well samples. These show that the valence band offset, when expressed as a fraction of the total band discontinuity, is a function of the alloy concentration x in the barrier.
TL;DR: In this paper, an investigation of the photoreflectance and photoluminescence spectra of 45 period ZnS-ZnSe strained layer superlattice having well and barrier widths of 3.3 and 3.7 nm, respectively, is reported.
Abstract: An investigotion of the photoreflectance and photoluminescence spectra of 45 period ZnS-ZnSe strained layer superlattice having well and barrier widths of 3.3 and 3.7 nm, respectively, is reported. Heavy hole (e 1 hh 1 ) and light hole (e 1 lh 1 ) excitons are well resolved in the 2 K photoreflectonce spectrum. The energies of these transitions are calculated within the envelope function framework, generalized to strained layers. The valence and conduction band offsets are the principal parameters in this calculation. Thus, two different approaches are set in competition to determine these quantities. The first is based on theoretical models while the second uses a «semi-experimental» method. The latter method gives a free-standing type-I superlattice with optimal agreement between photoreflectance measurements and theory. Also the importance of a precise knowledge of the exciton binding energy (enhanced because of the reduced dimensionality) for an accurate bond offset determination is shown. This binding energy is estimated for the heavy hole exciton from a variational calculation
TL;DR: In this article, a modified version of Kroemer's capacitance-voltage profiling method is developed wherein a quantum well is profiled instead of a single heterojunction, and a one-dimensional Poisson-Schrodinger solver is used to fit the reconstructed carrier profiles corresponding to a value of ΔEc at varying temperatures.
Abstract: The conduction band alignment of compressively strained In1−xGaxP relative to lattice matched InGaP/GaAs has been determined by capacitance-voltage profil-ing. A modified version of Kroemer’s capacitance-voltage profiling method is developed wherein a quantum well is profiled instead of a single heterojunction. A one-dimensional Poisson-Schrodinger solver was used to fit the reconstructed carrier profiles corresponding to a value of ΔEc at varying temperatures. Schottky barrier diode structures containing a single strained InGaP quantum well were grown by low pressure metalorganic chemical vapor deposition. The two strained compositions studied contained 35 and 31% gallium. Conduction band offsets of 101 and 131 meV were found for the 35 and 31% samples, respectively, with an estimated accuracy of ±5 meV. These results agreed closely with values predicted by empirical calculations.
TL;DR: In this article, a series of ZnSe/ZnS 0.25 Se 0.75 single quantum well (SQW) of various well thicknesses are grown on (001) GaAs with low pressure metalorganic vapour phase epitaxy (MOVPE).
Abstract: A series of ZnSe/ZnS 0.25 Se 0.75 single quantum wells (SQW) of various well thicknesses are grown on (001) GaAs with low pressure metalorganic vapour phase epitaxy (MOVPE). Photoreflectance measurements (PR) show pronounced structures which are assigned to excitonic transitions between quantum well states. The structural properties of the samples are determined with high resolution X-ray diffraction and transmission electron microscopy. The model of Mathieu et al. is used to calculate excitonic states in a QW and a fitting procedure is developed which allows an estimate of the band offset. The structure exhibits a type II alignment which is also supported by photoluminescence (PL) measurements and which is mainly the result of a strain induced shift of the ZnS 0.25 Se 0.75 conduction band.
TL;DR: In this article, the authors used an internal photo-emission technique to determine the band offsets between CdSe and amorphous hydrogenated Si films for the valence and conduction bands.
TL;DR: In this paper, the mismatch of electron or hole effective masses in compound materials of semiconductor heterostructures leads to a sizable renormalization of the band offsets in the three following cases: (i) exciton in a quantum well; (ii) electron (hole) in a rectangular quantum wire; (iii) superlattice in a magnetic field oriented along the growth direction.
Abstract: We show that the mismatch of electron or hole effective masses in compound materials of semiconductor heterostructures leads to a sizable renormalization of the band offsets in the three following cases: (i) exciton in a quantum well; (ii) electron (hole) in a rectangular quantum wire; (iii) superlattice in a magnetic field oriented along the growth direction. Additional effects are the anisotropy of electron effective mass in Bastard boundary conditions for case (ii) and negative magnetoresistance for case (iii).
TL;DR: In this paper, the authors measured the conduction-band discontinuity ΔEc in p−In0.53Ga0.47As/n−InP heterojunctions with a Si δ layer (1×1012 cm−2) inserted in InP at 10 A from the interface.
Abstract: We measured by internal photoemission the conduction‐band discontinuity ΔEc in p‐In0.53Ga0.47As/n‐InP heterojunctions with a Si δ layer (1×1012 cm−2) inserted in InP at 10 A from the interface. The n‐type Si δ doping induced an inhomogeneous and temperature‐dependent conduction‐band offset reduction as revealed by two onsets in the spectral response. The first one was absent in room‐temperature data and was due to the Si intralayer presence. The second correlated with the conduction‐band discontinuity value for heterojunctions without δ doping and its presence served as an indication of the inhomogeneity of the Si δ layer. The measured value of the modification was 0.11±0.04 eV in good agreement with the calculated one. Current‐voltage measurements confirmed that the Si δ layer modified the transport parameters of the heterojunction only at low temperature.
TL;DR: In this article, the authors used density functional theory in the local density approximation and norm-conserving pseudopotentials to calculate the valence band offset (VBO) at a ZnSe/ZnTe interface grown in the (100) direction.
Abstract: We use the density functional theory in the local density approximation and norm-conserving pseudopotentials to calculate the valence band offset (VBO) at a ZnSe/ZnTe interface grown in the (100) direction. The obtained VBO value of 1.09 eV is in excellent agreement with the corresponding experimental data and with other calculations.