InAs Conduction Band Research Articles

Heterostructure interface effects on the far-infrared magneto-optical spectra of InAs/Gasb quantum wells

The electronic and optical properties of InAs/GaSb heterostructures depend on the type of bonding at the interfaces, InSb bonds or GaAs bonds. We have studied cyclotron resonance (CR) in the far-infrared on two samples, each consisting of a single 30 nm InAs quantum well surrounded by thick GaSb barriers. The only intended difference between the samples is the interface bonding type, Ga–As bonds and In–Sb bonds. The CR for the sample with Ga–As interface bonds shows two lines whose positions are determined by nonparabolicity effects, whereas the sample with In–Sb bonds shows multiple lines due to strong cross-interface coupling between the InAs conduction band Landau levels (LLs) and the valence band LLs in GaSb. We find that the CR is a sensitive probe of interface bonding type for such structures.

A Theory of Charge Transport Due to Electron?Hole Recombination in Type II Semiconductor Quantum Well Devices

Activationless electron-hole generation and recombination in type II semimetallic single and double quantum wells is studied. An 8 x 8 k . p matrix Hamiltonian, and the transfer matrix method, is used to calculate the recombination rates for quantum wells made from InAs and GaSb. This model includes the non-parabolicity and anisotropy of the energy band structure. Because the conduction band of InAs lies beneath the valence band of GaSb, the generation and recombination processes do not require extra excitation particles such as phonons or photons. The effect of externally applied electric and magnetic fields is also included in the calculation of the recombination rates and both n-type and p-type single and double quantum wells are considered.

Comparison of InGaSb/InAs superlattice structures grown by MBE on GaSb, GaAs, and compliant GaAs substrates

This paper contains the characterization results for indium arsenide/indium gallium antimonide (InAs/InGaSb) superlattices (SL) that were grown by molecular beam epitaxy (MBE) on standard gallium arsenide (GaAs), standard GaSb, and compliant GaAs substrates. The atomic force microscopy (AFM) images, peak to valley (P-V) measurement, and surface roughness (RMS) measurements are reported for each sample. For the 5 µm×5 µm images, the P-V heights and RMS measurements were 37 A and 17 A, 12 A and 2 A, and 10 A and 1.8 A for the standard GaAs, standard GaSb, and compliant GaAs respectively. The high resolution x-ray diffraction (HRXRD) analysis found different 0th order SL peak to GaSb peak spacings for the structures grown on the different substrates. These peak separations are consistent with different residual strain states within the SL structures. Depending on the constants used to determine the relative shift of the valance and conduction bands as a function of strain for the individual layers, the change in the InAs conduction band to InGaSb valance band spacing could range from +7 meV to −47 meV for a lattice constant of 6.1532 A. The cutoff wavelength for the SL structure on the compliant GaAs, control GaSb, and control GaAs was 13.9 µm, 11 µm, and no significant response, respectively. This difference in cutoff wavelength corresponds to approximately a −23 meV change in the optical gap of the SL on the compliant GaAs substrate compared to the same SL on the control GaSb substrate.

A high-resolution photoemission study of confined metal systems on InAs(110)

Metal deposition on semiconductor substrates can give rise to various low-dimensional ordered structures. Their insulating or metallic character can depend on the spatial confinement and on the different atomic geometry. High-resolution and high-luminosity ultraviolet photoelectron spectroscopy is the best suited technique to follow the spectral density evolution of low-dimensional metallic systems deposited on narrow-gap semiconductors, in the energy gap region and close to the Fermi level. Simple metals, like alkali metals (Cs), produce one-dimensional insulating chains on InAs(110), while Bi builds up different symmetry structures with insulating [(1×1)] or metallic [(1×2)] character, and Ag presents an insulator-to-metal transition as a function of coverage. Moreover, high-resolution photoemission brings to light clear two-dimensional quantized eigenstates due to the quantum confinement of accumulated electron charge within the InAs conduction band, induced by InAs surface modifications.

Metal-induced gap states at InAs(110) surface

High-luminosity and high-energy-resolution photoemission spectroscopy can provide direct observation of the spectral density of metal-induced states throughout the whole band gap, even at extremely low metal deposition. We present a study of the density of states of a two-dimensional electron gas induced in the InAs(110) conduction band by deposition of caesium, antimony and silver adatoms. We follow the density of states redistribution between the two-dimensional electron-gas channel and the appearance of metal-induced gap states.

Intersubband transitions in InAs/GaSb superlattices in a parallel magnetic field

We present a theoretical study of intersubband transitions (IST) in InAs/GaSb superlattices in the presence of a parallel magnetic field. Starting from a model describing a single electron in a single quantum well and extending it to include many-body effects and the non-parabolicity of the InAs conduction band we are able to explain the recent cyclotron resonance experiments on narrow and wide InAs/GaSb quantum wells.

Exciton wave function, binding energy, and lifetime in InAs/GaSb coupled quantum wells

We studied theoretically excitons in narrow-coupled InAs/GaSb quantum wells where there is not any overlap between the InAs conduction subband and the GaSb valence subband. In this case, excitons do not exist in the equilibrium and the luminescence of pumped excitons can be observed. We calculated the exciton binding energy making use of the variational method. The resulting binding energy is around 4 meV. We also calculated the exciton lifetime for both radiative recombination and nonradiative recombination. Due to the unique band alignment of InAs/GaSb, the recombination can happen via two channels: first, mixing of the conduction band of InAs with the valence band of GaSb and second, electron tunneling from InAs conduction band to GaSb conduction band and hole tunneling from GaSb valence band to InAs valence band. The fastest recombination process is the radiative process in the second channel. The lifetime varies with the well widths from 45 ps for narrow wells to 400 ps for wider wells.

Evidence for electron-hole hybridization in cyclotron-resonance spectra of InAs/GaSb heterostructures

Cyclotron-resonance (CR) experiments have been performed on InAs/GaSb/AlSb double structures, in which electron and hole layers are separated by AlSb barriers. The strength of the electron-hole coupling is altered by varying the barrier width. Our data reveal that properties of InAs/GaSb systems with AlSb barriers thinner than 1.5 nm are entirely determined by interlayer tunneling and the CR features in such samples can be explained by hybridization between states in the InAs conduction band and in the GaSb valence band.

High magnetic field far-infrared spectroscopy of spatially separated electron–hole layers

Cyclotron resonance (CR) experiments have been performed on InAs/GaSb structures, in which InAs (electron) and GaSb (hole) layers are separated by AlSb barriers. Our data reveal that properties of InAs/GaSb systems with AlSb barriers thinner than 1.5 nm are entirely determined by interlayer tunneling and the CR features in such samples can be explained by hybridization between states in the InAs conduction band and in the GaSb valence band. The hybridization gap has been estimated from CR spectra for two samples with different degrees of electron–hole coupling. The CR spectra of widely separated electron–hole layers (with barriers thicker than 2 nm) are characterized by pronounced spin splitting. In addition to multiple spin–split CR lines new lines have been observed at high magnetic fields (11–13 T).

InAs/GaSb interfaces; the problem of boundary conditions

We present here a derivation of phenomenological boundary conditions for envelope functions at the interface between an InAs layer and a GaSb layer. The overlap of the valence band of GaSb with the conduction band of InAs leads to a coupling between electrons with total angular momentum 1/2 and holes with total angular momentum 3/2. The method that we use to match these wave-functions is that of the minimizing of the total energy of the system including the surface energy. We consider the different spinor characters of the states explicitly, and derive the required boundary conditions, which are not dependent on any specific microscopic model. The proposed approach is general, and may be used to obtain boundary conditions for other complicated cases of interfaces.

Saturation spectroscopy of electronic states in a magnetic field in InAs/Al xGa 1− xSb single quantum wells

We have carried out saturation spectroscopy of cyclotron resonance in a semiconducting InAs/Al 0.5Ga 0.5Sb single quantum well using the UCSB free electron laser and have extracted an effective Landau level lifetime using an n-level rate equation model. The effective lifetime shows strong oscillations (>an order of magnitude) with frequency. Minima are shifted to higher frequencies than those given by the simple parabolic magnetophonon resonance condition due to large nonparabolicity in the InAs conduction band. We have also used this technique to investigate the origins of two lines: the X-line and cyclotron resonance in a “semimetallic” InAs/Al 0.1Ga 0.9Sb single quantum-well structure. Results show that the two lines are of different origin.

Scanning tunneling spectroscopy on n-InAs(110): Landau-level quantization and scattering of electron waves at dopant atoms

Spatially resolved I./V.-images exhibit circular symmetrical corrugations at the surface. These are ascribed to scattered electron waves at dopant atoms below the surface. From the energy dependence of their diameter, the dispersion of the InAs conduction band at the Γ-point is estimated.

Barrier height at clean Au/InAs(100) interfaces

Using photoelectron spectroscopy, we have reexamined the barrier height at Au/InAs(100) contacts prepared under ultrahigh vacuum conditions. The n-barrier height is 0.010±0.050 eV: the Fermi level at the interface is right at the InAs conduction band edge. This result is expected from models based on charge transfer into metal-induced gap states but contrasts with previously published experimental values. Depending on the preparation procedure, the surface of InAs(100) grown using molecular-beam epitaxy shows c(4×4) or (2×4) reconstruction; the barrier height, however, is independent of the surface reconstruction prior to gold deposition.

Landau damped intersubband plasmons in [formula omitted] quantum wells

We present a combined theoretical and Raman scattering study of coupled intersubband plasmon-LO phonon modes in InAs AlSb quantum wells, highlighting the importance of the InAs conduction band nonparabolicity in such systems. We demonstrate that under the illumination conditions of the Raman measurements, electron densities can be as high as 4 × 10 12 cm −2 and give evidence of Landau damping of intersubband plasmons.

Electronic structure of InAs/GaAs self-assembled quantum dots.

The electronic properties of the self-assembled InAs/GaAs quantum dots are investigated theoretically. In our calculation the microscopic distribution of the strain, valence-band mixing, and the shape of the conduction band of InAs with strain are fully taken into account. New states are brought to light and their status in the framework of established approximate models of the electronic structure is critically examined.

Semimetal-semiconductor transition in InAs [sbnd]GaSb heterostructures

In a heterostructure consisting of neighboring layers of InAs and GaSb in a large band-gap host like AlSb, the bottom of the InAs conduction band lies ∼150meV below the top of the GaSb valence band. However, because the electron and hole subbands are weakly coupled for non-zero values of the wavevector k ∥ along the layer, an anticrossing of the levels occurs at k ∥ = k c, where k 2 c = (2μ/ħ 2) (Δ−ε v 0−ε c 0). Here Δ is the band overlap, ε c 0 and ε v 0 are the lowest electron and hole subband energies, and μ is the reduced mass. The splitting is in the order of 5–10 meV. For an intrinsic material, the Fermi level lies in this gap, so that no semimetallic state occurs. If the InAs layers are sufficiently wide, or if an electric field can be applied across the heterostructure (by fabricating front and back gates) it is possible to have the first excited electron subband ε c 1 realize an anticrossing with ε v 0 as well. Then a true semimetallic state can occur with a circle of electrons in the ε c 1 subband near k ∥ = 0, and a ring of holes near the anticrossing in the hybridized valence subband. A semimetal-to-semiconductor transition should occur, which is driven by shifting the single-particle subband energies with an applied electric or magnetic field.

High pressure studies of negative differential resistance in InAs/GaSb resonant conduction heterostructures

A single heterojunction of n-InAs/p-GaSb behaves as a two dimensional electron gas (2DEG) back to back with a two dimensional hole gas (2DHG), due to overlap between the GaSb valence band and the InAs conduction band. An unusual feature is the possibility of growing a ‘ light’ GaAs or a ‘ heavy’ InSb interface. The two interface types are predicted to give rise to different electronic and vibrational properties, while the existence of monolayer steps or interdiffusion could give rise to a mixed interface character. In this paper we demonstrate that vertical transport measurements as a function of pressure are a sensitive way of probing the electronic structure of the interface. On biasing InAs negative with respect to GaSb, electron transfer takes place from the 2DEG to the 2DHG, and the current initially increases with bias. At a critical bias, quantum confinement raises the energy of the 2DEG above that of the 2DHG and a region of Negative Differential Resistance (NDR) then occurs. The size of the NDR feature and the critical bias are both reduced by hydrostatic pressure, showing that the band overlap decreases. For a number of samples grown with a heavy interface by atmospheric pressure metalorganic vapour phase epitaxy the NDR vanishes at a threshold, P c ~ 12 ± 2 kbar. This threshold is consistent with a band overlap of 120 ± 20 meV and a shift of −10 meV/kbar. The NDR properties are found to be very sensitive to the detailed sequence of switching of the precursors during interface growth, as well as to the interface type.

Characterization of InAs‐GaSb type II superlattices grown by metal organic chemical vapor deposition

Abstract It was observed that the conduction‐band minimum of InAs is lower in energy than the valence‐band maximum of GaSb. This will cause the non‐rectification characteristic. Such unusual nonrectifying p‐n junction is the direct consequence of interpenetration between the GaSb valence band and the InAs conduction band, since the InAs‐GaSb superlattices can have a band gap smaller than that of either constituent materials. InAs‐GaSb superlattices have the modifiable band gap, but the absorption coefficient shall decrease rapidly when the period thickness is over 100 A(d 1=d 2). It has a good spectral response in 3–5 μm region, but bad in 8–14 μm. The new proposal offered a normal incidence valence intersubband transition at ∼10μm. It is potential to fabricate the long wavelength devices. In this paper, the InAs‐GaSb superlattices were grown by MOCVD. The quality is determined by x‐ray double crystal rocking curves. The period thickness is determined by High Resolution Transmission Electron Microscopy (H...

Magnetotransport measurements on InAs-GaSb quantum wells with the application of hydrostatic pressure

We present a series of magnetotransport measurements on high mobility single InAs-GaSb semimetallic quantum wells using hydrostatic pressures up to 10 kbar and temperatures down to ~100mK. Clearly defined, hole-related peaks in pϱ xx close to integer electronic filling factors in the semimetallic regime, have a stronger temperature dependence than the electron Shubnikov-de Haas effect at millikelvin temperatures and with this additional structure, apparent in ϱ xx the quantum Hall plateaux in ϱ xy deviate from h ve 2 , where v is the filling factor. The decrease in the electron concentration, dn 0 dp is 3.0 × 10 10 cm −2 kbar −1 in the dark, and 4.0 × 10 10 cm −2kbar −1 in the dark following infrared illumination to reduce the Fermi energy. We relate this reduction in the electron and hole concentrations to the uncrossing of the InAs conduction band and the GaSb valence band and to the role played by a GaSb surface donor at high pressures. The fermi energy at the surface is pinned approximately 250 meV above the GaSb valence band edge.

Giant third-order nonlinear susceptibilities for in-plane far-infrared excitation of single InAs quantum wells

Third-order, free-carrier nonlinear susceptibilities, χ (3), have been measured between 19 and 23 cm −1 for three InAs/AlSb quantum wells with sheet densities between 2.5 × 10 12 cm −2 and 8 × 10 12 cm −2. We find that these wells are strongly nonlinear at far-infrared frequencies: odd harmonics ninth order have been observed at high incident intensities, and the peak value of χ (3) reaches ∼ 1 esu. This is several orders of magnitude larger than previously reported values for χ (3) in bulk n-GaAs (10 −4 esu)[1] and in polyacetylen (10 −7 esu)[2]. The large magnitude of χ (3) is attributed to the high carrier density in the InAs wells, and to the strong non-parabolicity of the conduction band in InAs. However, the free-carrier χ (3) for bulk InAs predicts a density-dependence different from that observed, and the measured decrease in χ (3) with increasing intensity indicates non-perturbative response. We find that the anisotropy of χ (3) displays the expected 4-fold symmetry.