Value Of ΔEv Research Articles

GaInP–AlGaInP band offsets determined from hydrostatic pressure measurements

Low-temperature (1.8 K) photoluminescence spectra of a Ga0.52In0.48P–(Al0.58Ga0.42)0.52In0.48P multiple quantum well have been measured as a function of hydrostatic pressure from 0 to 5.0 GPa. The extrapolation to zero pressure of the energy of the indirect k-and-real-space barrier X to well Γ transition allows the direct determination of the valence band offset for this heterojunction system. A value of ΔEv=(0.35±0.05)ΔEg is found, in good agreement with values previously determined from the theoretical modeling of quantum well transition energies.

Photoelectric-Yield Studies of c-Si/a-Si:H Interfaces

ABSTRACTWe report the first yield spectroscopy study on well characterized c-Si/a-Si:H heterojunctions grown in situ under UHV conditions. We find that this spectroscopy, when operated in the constant final state mode, allows a direct and precise determination of the valence-band discontinuity at the interface. A value of δEv = 0.44 ± 0.02 eV was found for the discontinuity.

PHOTOEMISSION STUDY OF VALENCE BAND DISCONTINUITY OF Si/GaP(Ⅲ)HETEROINTERFACE

The growth procedure of the Si/GaP( Ⅲ )heterointerface with Si electron beam evaporation in an improved ADES-400 photo-electron spectrometer is introduced in this paper. Then the status of formation and valence band discontinuities of Si/GaP(Ⅲ ) heterointerfaces that grown under different conditions are analysed or measured in situ by photoemission. The relation of the ΔEv values with the status of the interface and the shift of atomic core levels is discussed. The growth condition of the abrupt and ordered Si/GaP(Ⅲ)heterointerfaces is determined. The value of valence band discontinuity in this case is 0.80eV. It agrees with theoretical results.

ELECTRONIC STRUCTURE OF STRAINED SUPERLATTICES (InAs)n(lnP)n(001):ab initio LMTO CALCULATION

The electronic structure of strained superlattices (SLS) (InAs)n(InP)n(001) are calculated with the Linearized-Muffin-Tin Orbitals (LMTO) band structure method in which the higher energy unoccupied d orbitals are treated by internal summation approach. The effects of In 4d orbitals on band structures are investigated. The valence band offsets (ΔEv) at SLS's are determined by a frozen-potential approach. The results show the bulk-like property is almost recovered in the molecular layers next to the interfaces. The band structure of (InAs)1(InP)1(001) given by the present work is well consistent with those given by more elaborate FLAPW calculation. The ΔEv values determined by the present calculation are in good agreement with those from XPS measurement and FLAPW method in which the core level or the macroscopic average potentials is used as a reference level. The small calculation effort and the satisfactory precision justify the present method as a very effective means for studying the electronic structures of multi-layers SLS.

Effect of interface composition on the band offsets at InAs/AlSb (001) heterojunctions

X-ray photoemission spectroscopy has been used to directly measure the dependence of the valence band offset ΔEv on interface composition (AlAs-like versus InSb-like) for InAs/AlSb (001) heterojunctions grown by molecular-beam epitaxy. A staggered band alignment with a consistent average value of ΔEv = 0.16 eV is measured for three samples with the InSb-like interface. A difference of 0.07 eV is observed between the average ΔEv values for two AlAs-like interface samples (0.15 and 0.22 eV, respectively). The growth-to-growth variation in ΔEv value for the AlAs-like interface, and the 0.06 eV difference between the InSb-like ΔEv value and the larger AlAs-like ΔEv value are both attributed to interface composition differences. We interpret the ΔEv = 0.22 eV value as being most characteristic of the AlAs-like interface. A tight binding model calculation of the effect of local strain on InAs/AlSb band offsets is compared to experiment.

Measurement of InP/In0.53Ga0.47As and In0.53Ga0.47As/In0.52Al0.48As heterojunction band offsets by x-ray photoemission spectroscopy

X-ray photoemission spectroscopy (XPS) has been used to measure the valence-band offset ΔEv for the lattice-matched InP/ In0.53Ga0.47As and In0.53Ga0.47As/ In0.52Al0.48As heterojunction interfaces. The heterojunctions were formed by molecular-beam epitaxy. We obtain values of ΔEv (InP/In0.53Ga0.47As) =0.34 eV (ΔEc/ ΔEv=43/57) and ΔEv (In0.53Ga0.47As/ In0.52Al0.48As) =0.22 eV (ΔEc/ ΔEv =68/32) for the respective interfaces. By combining these measurements with available XPS ΔEv (InP/ In0.52Al0.48As) data we find that band offset transitivity is satisfied. Accordingly, the band offsets for heterojunction pairs formed from InP, In0.53Ga0.47As, and In0.52Al0.48As are not influenced by interface specific effects.

Measurement of AlAs/InP and InP/In0.52Al0.48As heterojunction band offsets by x-ray photoemission spectroscopy

X-ray photoemission spectroscopy (XPS) has been used to measure the valence band offsets at the x=0 and x=0.52 points of the InxAl1−xAs/InP(100) heterojunction system. For the lattice-matched interface we determine a value of ΔEv(InP/In0.52Al0.48As)=0.16 eV (staggered band alignment). Although the pseudomorphic AlAs/InP(100) interface investigated is strained, the ΔEv(AlAs/InP)=−0.27 eV (nested band alignment) value obtained by the XPS analysis method used is interpreted as being characteristic of an unstrained interface.

Conduction- and valence-band offsets in GaAs/Ga0.51In0.49P single quantum wells grown by metalorganic chemical vapor deposition

We have independently estimated the conduction- and valence-band offsets ΔEc and ΔEv in GaAs/Ga0.51In0.49P quantum wells by measuring the capacitance transient resulting from thermal emission of carriers from the respective wells. The heterostructure samples were grown by low-pressure metalorganic chemical vapor deposition. The band offsets are extrapolated from the emission activation energies with appropriate corrections. The estimated values of ΔEc and ΔEv are 0.198 and 0.285 eV, respectively.

Determination of band line-up in β-SiC/Si heterojunction for Si-HBT's

We measured the band discontinuity of the β-SiC/Si heterojunction by photoemission to determine its application to Si-heterojunction bipolar transistors. We measured the valence band discontinuity, ΔEv, as 0.54±0.15 eV. We calculated the conduction band discontinuity, ΔEc, as 0.54 eV. The band line-up was determined using these values of ΔEv and ΔEc when the heterojunction of n-type β-SiC/p-type Si was formed. As a result, the holes in Si feel a potential barrier about 1 eV higher than the electrons in the n-type β-SiC feel at the heterojunction. This band line-up is attractive for Si-HBT's because the holes in the Si base reverse-injected into the SiC emitter are negligible, resulting in higher current gain.

Band offsets and deep defect distribution in hydrogenated amorphous silicon-crystalline silicon heterostructures

Voltage filling pulse measurements taken on a-Si:H/c-Si heterostructure Schottky diode samples are used to examine the capture of electrons from the c-Si substrate into a-Si:H defect states. These measurements, along with the capacitance versus temperature spectra of these diodes, indicate a nearly zero conduction-band offset (50±50 meV). In addition, we have observed trapping of holes at the valence-band discontinuity ΔEv. A clear threshold for the subsequent optical release of these holes yields a value of ΔEv =0.58±0.02 eV. Our measurements also provide the energy and spatial distribution of deep defects within the a-Si:H layer and indicate a region of anomalously large defect density (1018 cm−3) within roughly 350 Å of the a-Si:H/c-Si interface.

X-ray photoelectron spectroscopy study of band offsets in a-Si0·2C0·8:H/p-(a-Si:H) and a-Si0·2C0·8:H/n-(a-Si:H) heterojunctions

Abstract Valence-band offsets ΔEv have been evaluated from an X-ray photoelectron spectroscopy (XPS) study of heterojunctions of a-Si0·2C0·8:H/p-(a-Si:H) and a-Si0·2C0·8:H/n-(a-Si:H). The values of ΔEv for a-Si0·2C0·8:H/p-(a-Si:H) heterojunctions are estimated to range from 1·2 ± 0·05 to 1·5 ± 005 eV depending on the amounts of dopant in the a-Si:H. For a-Si0·2C0·8:H/n-(a-Si:H), ΔEv is 0·7 ±005eV. The origin of the difference in the values for different types and levels of doping in a-Si: H is discussed. Reported electron transport properties are discussed using the band structure at the hetero-interfaces obtained from the present XPS study.

GaAs/InP and InAs/InP heterojunction band offsets measured by x-ray photoemission spectroscopy

X-ray photoemission spectroscopy (XPS) has been used to measure the unstrained valence-band offset ΔEv for the x=0 and x=1 end points of the Inx Ga1−x As/InP (100) heterojunction system. Although the GaAs/InP (100) and InAs/InP (100) pseudomorphic interfaces investigated are strained because of lattice mismatch, the ΔEv values obtained by the XPS measurement analysis used are interpreted as characteristic of an unstrained interface. Strain-free values of ΔEv (GaAs/InP)=0.19 eV and ΔEv (InAs/InP)=0.31 eV are reported. A linear interpolation of these x=0 and x=1 unstrained values gives ΔEv (In0.53 Ga0.47 As/InP)=0.25 eV (ΔEc/ΔEv =58/42) for the lattice-matched interface.

Measurement of GaAs/InP and InAs/InP heterojunction band offsets by x-ray photoemission spectroscopy

The unstrained valence-band offset ΔEv for the x=0 and x=1 end points of the InxGa1−xAs/InP (100) heterojunction system has been measured by x-ray photoemission spectroscopy (XPS). Although the GaAs/InP and InAs/InP interfaces are strained because of lattice mismatch, the ΔEv values obtained by the XPS measurement method used are characteristic of an unstrained interface. Values of ΔEv (GaAs/InP)=0.19 eV and ΔEv (InAs/InP)=0.31 eV are observed. A linear interpolation between the x=0 and x=1 values gives ΔEv (In0.53 Ga0.47As/ InP)=0.25 eV for the x=0.53 lattice-matched interface (ΔEc /ΔEv =58/42).

Temperature-Dependent Infrared Absorption of Hg-Based II-VI Semiconductor Superlattices

ABSTRACTThe optical absorption of a series of HgTe/Cd0.85 Hg0. 15 Te superlattices (SLs) have been measured in the spectral region from 2 to 12 µm at temperatures from 300 K down to 4.2 K. Several subband transitions were identified and their transition energies were compared with theoretical calculations, with the valence band offset δEv between HgTe and CdTe as a fitting parameter. It is found that at a given temperature, a value of δEv = 420 ± 100 meV fits the results of all the SLs, and δEv does not depend on temperature to within ±100 meV.

Band Offsets and Anomalous Deep Defect Distribution at the Hydrogenated Amorphous Silicon-Crystalline Silicon Interface via Junction Capacitance Techniques

ABSTRACTA novel a-Si:H/c-Si Schottky diode heterostructure device premits the study of the capacitive response to relatively low temperatures (25 K) and also allows fast pulse filling capture measurements of electrons from the c-Si substrate into a-Si:H defect states. These latter measurements, as well as capacitance vs. temperature measurements on these diodes, indicate a nearly zero conduction band offset (50±50 meV). We also have observed trapping of holes at the a-Si:H/c-Si valence band discontinuity ΔEv. A clear threshold for the subsequent optical release of these trapped holes by sub-bandgap light yields a value of ΔEv = 0.58±0.02 eV. Finally, photocapacitance spectra along with thermally stimulated capacitance (TSCAP) measurements indicate an anomalously large (l×1018/cm3) Gaussian-shaped defect band located a Ec - 0.88 eV with a FWHM of 0.46 eV. Model calculations of the high temperature capacitance-voltage dependence indicate these defects lie predominately within 350 Å of the a-Si:H/c-Si interface.

Effect of growth sequence on the band discontinuities at AlAs/GaAs (100) and (110) heterojunction interfaces

The valence band discontinuity ΔEv for the AlAs grown on GaAs (AlAs–GaAs) heterojunction interface is compared to the corresponding ΔEv for the GaAs grown on AlAs interface (GaAs–AlAs) for both (100) and (110) crystallographic orientations by using x-ray photoemission spectroscopy (XPS). Molecular-beam epitaxy within the XPS system was used to prepare the samples. The XPS method has the feature that ΔEv differences are measured more accurately than the corresponding absolute magnitudes. For the (100) interface, the value of ΔEv(AlAs–GaAs) is 0.10±0.02 eV larger than ΔEv(GaAs–AlAs). For the (110) interface, ΔEv(AlAs–GaAs) is 0.13±0.04 eV larger than ΔEv(GaAs–AlAs). The average discontinuity magnitudes are: ΔEv(AlAs–GaAs)(100)=0.46 eV; ΔEv(GaAs–AlAs)(100)=0.36 eV; ΔEv(AlAs–GaAs)(110)=0.55 eV; and ΔEv(GaAs–AlAs)(110)=0.42 eV. Thus, both a growth sequence effect and an orientation dependence have been found to be intrinsic characteristics of the (100) and (110) AlAs/GaAs heterojunction interfaces. As a consequence, there is an inherent asymmetry in the potential wells associated with AlAs/GaAs quantum well and superlattice structures.

Determination of the (100) InAs/GaSb heterojunction valence-band discontinuity by x-ray photoemission core level spectroscopy

The valence-band discontinuity ΔEv has been determined for the (100) InAs/GaSb system by x-ray photoemission core level spectroscopy. For 20 Å of InAs on GaSb we find that ΔEv=0.53 eV. The reverse structure, consisting of a 20-Å layer of GaSb on InAs, gave a measured value of ΔEv=0.48 eV. Since the difference in these two values lies within our experimental uncertainty, we report an average offset of 0.51±0.1 eV. The large value of the valence-band discontinuity in this system shows the band lineup to be of the broken gap variety with the InAs conduction-band energy lying below that of the GaSb valence band. This result is in good agreement with theoretical predictions.

GaAs–Ge heterojunction interfaces: Cyclical behavior of band discontinuities

The valence band discontinuity ΔEv of (110) and (100) oriented heterojunctions made by growth of GaAs onto Ge (GaAs–Ge) is found to decrease with time after interface formation (on a scale of tens of hours). The thin, abrupt heterojunction samples were prepared by molecular beam epitaxy techniques and characterized by x-ray photoemission spectroscopy. The final room temperature value of ΔEv(GaAs–Ge) is >0.2 eV lower than the ∼0.56 eV value for the stable Ge–GaAs (reverse growth sequence) interface. Annealing a sample for several minutes in vacuum at the growth temperature increases ΔEv(GaAs–Ge) to approximately the Ge–GaAs value. By control of anneal time and an accompanying As overpressure, ΔEv(GaAs–Ge) can be cycled by >0.2 eV. This variation in an interface electrostatic dipole is apparently related to a variable amount of electrically active As that is located at the heterojunction interface. The dipole formation mechanism involved may require the presence of the antiphase disorder that is expected for growth of GaAs on Ge.

Energy band alignment in GaAs:(Al,Ga)As heterostructures: The dependence on alloy composition

The band alignment in GaAs:(Al,Ga)As heterostructures has been investigated over the full range of alloy composition. The valence-band discontinuity ΔEv is determined by measuring the activation energy for thermionic emission of holes from p-GaAs over an undoped, square (Al,Ga)As barrier. The use of p-type structures to measure ΔEv circumvents a number of complications involved in the measurement of ΔEc. The parameters required for analysis are determined by different measurements on the same structures and the analysis is performed so that the activation energy, extrapolated to zero bias, yields ΔEv directly. It is found that ΔEv is a linear function of the aluminum mole fraction xAl: ΔEv ≂0.55xAl (eV) (0≤xAl≤1). The validity of these data is supported by measurements of ΔEc in the direct band-gap regime, where complementary values of ΔEv and ΔEc add up to the expected band-gap difference. This relationship provides a simple description of the full band alignment in this heterosystem and should prove valuable as a test of the various heterojunction lineup theories. Moreover, these measurements have a number of important consequences, particularly from the viewpoint of heterojunction devices.

Measurement of ZnSe–GaAs(110) and ZnSe–Ge(110) heterojunction band discontinuities by x-ray photoelectron spectroscopy (XPS)

X-ray photoelectron spectroscopy was used to study the growth and energy-band alignment of ZnSe–GaAs(110) and ZnSe–Ge(110) heterojunctions. The ZnSe–GaAs heterojunctions were formed by growing ZnSe on GaAs(110). Growth temperatures were varied to produce both epitaxial and nonepitaxial interfaces. For ZnSe grown at ∠300 °C on GaAs(110), the valence- band discontinuity ΔEv was 0.96 eV; for ZnSe deposited at room temperature and crystallized at ∠300 °C, ΔEv is 1.10 eV. The Ge–ZnSe(110) interfaces were formed by depositing Ge(ZnSe) on ZnSe(Ge)(110) at room temperature, followed by ∠300 °C crystallization. The corresponding ΔEv’s were 1.52 and 1.29 eV, respectively. Our measured ΔEv values for epitaxial heterojunctions are compared with the predictions of theoretical models. Our results demonstrate that substantial interface structure dependent contributions to ΔEv can occur at Ge–ZnSe(110) and GaAs– ZnSe(110) heterojunctions.