Showing papers on "Band offset published in 1985"

Valence band offset in AlAs/GaAs heterojunctions and the empirical relation for band alignment

Abstract: The valence band offset in AlAs/GaAs heterojunctions is found to be 0.45±0.05 eV from analysis of charge transfer versus undoped spacer layer thickness. This result and several recent experiments on AlxGa1−xAs/GaAs heterojunctions indicate that the valence band offset is approximately linear in AlAs fraction x over the entire alloy composition range and more than twice the previously accepted value. The relation between heterojunction band offsets and Fermi level pinning for metals on semiconductors is discussed.

Determination of heterojunction band offsets by capacitance‐voltage profiling through nonabrupt isotype heterojunctions

Abstract: It is shown that the capacitance‐voltage (C‐V) profiling technique to obtain heterojunction (HJ) band offsets is grading independent, that is, the band offset values obtained by it are the values for the limit of zero compositional grading, even in nonabrupt junctions. The result explains the good agreement of old data taken on nonabrupt HJ’s grown by liquid phase epitaxy (LPE) with more recent data on abrupt junctions. It suggests that LPE grown HJ’s may be used more freely than was previously thought to determine those offsets, making C‐V profiling the most versatile technique for the determination of HJ band offsets.

Optical investigation of hole and electron subbands in HgTe-CdTe superlattices.

Abstract: Photoluminescence spectroscopy and resonant Raman scattering were applied to investigate electronic properties of HgTe-CdTe superlattices. It is established that the spin-orbit split-off valence states in the CdTe layers are quantized and that the small band offset affects the lifetime of the holes. Radiative recombinations from electron subbands in the HgTe square wells can be measured when the subband energies are close to the conduction-band edge of CdTe. The spectra suggest that relaxation processes in the HgTe subbands involve the emission of optical phonons.

Evidence of orientation independence of band offset in AlGaAs/GaAs heterostructures

Abstract: The valence-band offset between GaAs and AlGaAs has been found to be independent of crystal orientation, as deduced from measurements of the two-dimensional hole densities in ${\mathrm{Al}}_{026}$${\mathrm{Ga}}_{074}$As/GaAs heterojunctions An analysis of the charge transfer yields a valence-band offset of 039\ifmmode\pm\else\textpm\fi{}002 of the energy-gap difference

Burstein-Moss Effect of PbTe-Pb1-xSnxTe Superlattice

Abstract: Optical-absorption-edge shifts due to free carrier (Burstein-Moss effect) of PbTe-Pb1-xSnxTe (x=022) superlattices (SLs) were measured at 77 K to determine the band offset of the heterojunction For the n-type SL, the shift was very small owing to the electron confinement into PbTe wider gap layers resulting from a type-I' band structure On the other hand, a large shift was observed for the p-type SL owing to the electron confinement into Pb1-xSnxTe narrower gap layers Analyzing the optical absorption properties, conduction band edge of the Pb1-xSnxTe was estimated to be 60 meV higher than that of PbTe

Energy Band Structure

Abstract: The energy band structure is the relationship between the energy and momentum of a carrier in a solid. For an electron in free space, the energy is proportional to the square of the momentum. The factor of proportionality is 1/2 m 0, where m 0 is the free electron mass. In the simple model of band structure, the same relationship between energy and momentum is assumed except that m 0 is replaced by an effective mass m. This may be larger or smaller than m 0 . Why this is so will be seen later in this chapter. Quite often the band structure is more complex and can only be calculated semi-empirically even with computers. A short description of some typical band structures will be given in Sect. 2.4 and used for the calculation of charge transport in Chaps. 7, 8, while in Chaps. 4, 5, the transport properties will be calculated assuming the simple model of band structure (which is quite a good approximation for most purposes).

Effect of an Al interlayer on the GaAs/Ge(100) heterojunction formation

Abstract: The chemistry, structure, and growth kinetics of epitaxial GaAs/Ge heterojunctions are controllably modified using an Al interlayer of one to two monolayers in thickness. Photoemission spectroscopy is used to investigate the interface formation with and without the Al interlayer. Although the valence-band and core-level spectra indicate dramatic changes of the chemistry and structure caused by the Al (deposited on the substrates both at room temperature and at 340 \ifmmode^\circ\else\textdegree\fi{}C) at the interface, the band-structure lineup is not affected. The Fermi level in the gaps is influenced by both the presence of the Al interlayer and the deposition temperature. The Fermi level moves toward the valence band by 0.15 and 0.3 eV (relative to the GaAs c(4\ifmmode\times\else\texttimes\fi{}4)/Ge degenerate n-type interface) for room-temperature and 340 \ifmmode^\circ\else\textdegree\fi{}C deposition, respectively. The Fermi-level position is simply related to the amount of As diffusion into the Ge layer and its role as an n-type dopant. The results support the conclusion that the band offset is primarily an intrinsic (bulk) property which is insensitive to interfacial charge distribution or chemistry to within \ifmmode\pm\else\textpm\fi{}0.05 eV.

Internal Photoemission in GaAs/(AlxGa1−x)As Heterostructures

Abstract: Band offsets in (AlxGa1−x)As/GaAs heterostructures are determined using internal photoemission experiments. Onsets in the photocurrent are observed for photon energies exceeding the fundamental energy gaps of GaAs and (AlxGa1−x)As. Additional onsets occur at photon energies in the infrared region due to internal photoemission from the conduction band in GaAs over the barrier into the conduction band of (AlxGa1−x)As and in the near red region where excitations from the GaAs valence band into the (AlxGa1−x)As conduction band are involved. From the measured energies we determine ΔEc/ΔEg = 0.8 ± 0.03 for x = 0.2.

n+ InGaAs/nGaAs heterojunction Schottky diodes with low barriers controlled by band offset and doping level

Abstract: We have fabricated and measured low barrier (30–150 meV) Schottky diodes using n +InGaAs/nGaAs pseudomorphic structures with up to 1.5% lattice mismatch. The I‐Vmeasurements at temperatures from 4 to 200 K show rectifying behavior and indicate transport mechanisms which range from tunneling to thermionic emission. The transport properties and barrier height determinations indicate that the band offset is predominantly in the conduction band. The barrier height increases with In concentration, which is consistent with band calculations based on previous experimental data.

Sensitivity of defect energy levels to host band structures and impurity potentials in CdTe

Abstract: The sensitivity of defect energy levels in semiconductors to the host band structures and impurity potentials has been studied for approximately 30 impurities in CdTe using four different band-structure models. The discrepancies in the defect levels between two different sets of band structures and impurity potentials are found to range from less than 0.1 eV to the whole band gap (1.6 eV). The band-structure effects are analyzed here in terms of detailed partial densities of states. Examples of contradictory predictions from different band structures are illustrated, and ways to improve the theory are suggested.

Band offsets and the optical properties of HgTe‐CdTe superlattices

Abstract: The effect of variation in the band offset on the band gap and optical properties of the HgTe‐CdTe superlattice is examined. If we define the valence‐band offset ΔEν to be the energy of the valence‐band edge of the HgTe with respect to the valence‐band edge of the CdTe, both the band gap and optical properties are smooth functions about ΔEν≊0.

Superlattices: New Semiconductor Materials

Abstract: The possibility of producing man-made structures with very novel properties is discussed. To illustrate some of the possibilities, we consider the HgTe-CdTe superlattice, the strained-layer superlattice, and the transport through thin barrier layers.