InAs Films Research Articles

Optical characterization of InAs film grown on SnO2 substrate by the electrodeposition technique

Indium arsenide films have been grown by an electrodeposition process at low temperature on a tin oxide (SnO2) substrate. X-ray diffraction studies showed that the as-grown films are poorly crystallized and heat treatment improved the crystallinity of InAs films. Atomic force microscopic measurements revealed that the InAs film surface is formed by particles for which the grain size depends on the electrolysis parameters; we have found that the grain size increases with the electrolysis current density. Absorption measurements show that the band gap energy red-shifts with increasing particle size. This result can be interpreted as a consequence of the quantum confinement effect on the carriers in the nanocrystallites.

Time resolved measurements of spin and carrier dynamics in InAs films

We report time resolved measurements of spin and carrier relaxation in InAs films with carrier densities of 1.3×1016 and 1.6×1016cm−3 grown on (001) and (111) GaAs, respectively. We used standard pump-probe and magneto-optical Kerr effect spectroscopy at different excitation wavelengths, power densities, and temperatures. We observed sensitivity of carrier and spin relaxation time to the photoinduced carrier density but not to the variation in temperature. We explain our results using the Elliot–Yafet picture of spin relaxation process in narrow gap semiconductors.

InAs film grown on Si(111) by metal organic vapor phase epitaxy

We report the successful growth of high quality InAs films directly on Si(111) by Metal Organic Vapor Phase Epitaxy. A nearly mirror-like and uniform InAs film is obtained at 580 °C for a thickness of 2 μm. We measured a high value of the electron mobility of 5100 cm2/Vs at room temperature. The growth is performed using a standard two-step procedure. The influence of the nucleation layer, group V flow rate, and layer thickness on the electrical and morphological properties of the InAs film have been investigated. We present results of our studies by Atomic Force Microscopy, Scanning Electron Microscopy, electrical Hall/van der Pauw and structural X-Ray Diffraction characterization.

Electrical characterisation of Sn doped InAs grown by MOVPE

AbstractThe feasibility of tetraethyl tin (TESn) as an n‐type dopant for InAs is investigated. The electrical properties of Sn doped InAs films grown on semi‐insulating GaAs substrates by MOVPE are extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that Sn concentrations can be controlled over 2 orders of magnitude. The Sn doped InAs layers exhibit carrier concentrations between 2.7 x 1017 and 4.7 x 1019 cm–3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. Furthermore, the influence of the variation of these parameters on the structural properties of InAs are also reported. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spin Dynamics in Narrow-Gap Semiconductor Epitaxial Layers

We report on investigation of the spin dynamics in InAs and InSb films grown on GaAs at a temperature range from 77 K to 290 K. For both materials, the large lattice mismatch with the GaAs substrate results in the formation of an interface accumulation layer with a large defect concentration, which strongly affects the spin relaxation in these areas. Moreover, the native surface defect in the InAs films resulted in an additional charge accumulation layer with high conductivity, but very short spin lifetime. In contrast, in InSb layers, the surface states introduce a depletion region. We have correlated the spin relaxation with a multi-layer analysis of the transport properties, and find that in a 1 μm thick InAs film, approximately 70% of the total current flows through the interface and surface accumulation layers, which have sub-picosecond lifetimes, whereas in InSb films of the same thickness, the semiconducting layer carries more than 90% of the total current, and the spin lifetime in the accumulation layer is only slightly less than that of the central semiconducting layer. We suggest that InSb could be a more attractive candidate for spintronic applications than InAs.

Spin lifetime in high quality InSb epitaxial layers grown on GaAs

The spin relaxation in undoped InSb films grown on GaAs has been investigated in the temperature range from 77to290K. Two distinct lifetime values have been extracted, 1 and 2.5ps, dependent on film thickness. Comparison of this data with a multilayer transport analysis of the films suggests that the longer time (∼2.5ps at 290K) is associated with the central intrinsic region of the film, while the shorter time (∼1ps) is related to the highly dislocated accumulation region at the film-substrate interface. Whereas previous work on InAs films grown on GaAs showed that the native surface defect resulted in an additional charge accumulation layer with high conductivity but very short spin lifetime, in InSb layers the surface states introduce a depletion region. We infer that InSb could be a more attractive candidate for spintronic applications than InAs.

STM/STS Measurements of Two-Dimensional Electronic States in Magnetic Fields at Epitaxially Grown InAs(111)A Surfaces

The local density of states (LDOS) at the epitaxially grown InAs surface on a GaAs substrate was studied at very low temperatures in magnetic fields up to 6 T by scanning tunneling microscopy and spectroscopy. We observed a series of peaks, associated with Landau quantization of the two-dimensional electron system (2DES), in the tunnel spectra just above the subband energy (-80 meV) of the 2DES. The intervals between the peaks are consistent with the estimation from the effective mass of the 2DES at the InAs surface. In a wider energy range, another type of oscillation which was independent of magnetic field was also observed. This oscillation can be explained by the energy dependence of the transmission probability of the tunneling current through the Schottky barrier formed at the interface between the InAs film and GaAs substrate.

Interfacial structure, bonding and composition of InAs and GaSb thin films determined using coherent Bragg rod analysis

We have used Bragg rod x-ray diffraction combined with a direct method of phase retrieval to extract atomic resolution electron-density maps of a complementary series of heteroepitaxial III-V semiconductor samples. From the three-dimensional electron-density maps we derive the monolayer spacings, the chemical compositions, and the characteristics of the bonding for all atomic planes in the film and across the film-substrate interface. InAs films grown on GaSb(001) under two different As conditions (using dimer or tetramer forms) both showed conformal roughness and mixed $\mathrm{Ga}\mathrm{As}∕\mathrm{In}\mathrm{Sb}$ interfacial bonding character. The As tetramer conditions favored InSb bonding at the interface while, in the case of the dimer, the percentages corresponding to GaAs and InSb bonding were equal within the experimental error. The GaSb film grown on InAs(001) displayed significant In and As interdiffusion and had a relatively large fraction of GaAs-like bonds at the interface.

Spin lifetime inInAsepitaxial layers grown onGaAs

We report investigation of the spin relaxation in InAs films grown on GaAs at a temperature range from 77 K to 290 K. InAs is known to have a surface accumulation layer and the depth profile of the concentration and mobility is strongly nonuniform. We have correlated the spin relaxation with a multilayer analysis of the transport properties and find that the surface and the interface with the GaAs substrate both have subpicosecond lifetimes (due to the high carrier concentration), whereas the central semiconducting layer has a lifetime of an order of 10 ps. Even for the thickest film studied (1 micro-m, the semiconducting layer only carried 30% of the total current (with 10% through the interface layer and 60% through the surface accumulation layer). Designs for spintronic devices that utilize InAs, which is attractive due to its narrow gap and strong Rashba effect, will need to include strategies for minimizing the effects of the surface.

The evolution of the microstructure and morphology of metal-organic vapor-phase epitaxy-grown InAs films on (1 0 0) GaAs

The large lattice mismatch (7%) between InAs and GaAs leads to a complex microstructure with many misfit-derived defects. The dependence of the microstructure and morphology of InAs films, deposited on (1 0 0) GaAs substrates via metal-organic vapor-phase epitaxy (MOVPE), on growth parameters and the substrate miscut was studied. The InAs crystal microstructure was evaluated by X-ray diffraction rocking curves, pole figures and by cross-sectional transmission electron microscopy (TEM). At high growth temperatures and high V/III ratios, multiple tilting of the InAs crystal lattice resulted in domains misoriented by 4–7° with respect to each other. Low-angle grain boundaries separating the misoriented grains were observed in cross-sectional TEM micrographs. Low growth temperatures or low V/III ratios resulted in a singly oriented InAs film aligned with the GaAs. Atomic force microscopy (AFM) was employed to determine the surface morphology of InAs thin films and uncoalesced islands. The island areal number-density decreased and island size increased with increasing growth temperature. A smoother InAs surface morphology was observed for the films deposited at a low growth temperature or low V/III ratio. The early coalescence of smaller islands resulted in a single InAs orientation in the coalesced films. The observed effects are discussed in terms of the effect of an In-rich growth environment, resulting from the low growth temperature and low V/III ratio, on the InAs growth chemistry and the strain relaxation phenomena.

Quantum confinement in nanocorrugated semiconductor films

Numerical simulations were performed to predict the electron energy levels and wave functions in periodically nanocorrugated free-standing InAs films. The obtained data show that in films thinner than $4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ the lowest energy levels are due to the $X$-conduction-band valleys. In such films, the elastic strain gives rise to a periodic potential consisting of quantum wells about $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ deep, resulting from the strain-induced shift of the energy position of the $X$-valley minimum. The possibility of localization of electron states in the potential wells is shown.

Detection angle resolved PIXE and the equivalent depth concept for thin film characterization

AbstractThe characterization of thin films using PIXE, although basically a simple matter, in practice suffers from significant problems. Here two case studies are presented in which the use of grazing detection geometry is shown to be a good solution. The first case study, the analysis of GaSb–InAs films deposited on a GaSb substrate, relates to the measurement of elements of atomic number close to and below that of the substrate. Problems may be due to the tail of the peaks that correspond to x‐rays emitted from the substrate, and also to the presence in the substrate of an element having large x‐ray emission cross‐sections. The use of the simulation capability implemented on the DATTPIXE package is shown to be of good help in the proper planning of the analysis procedure. In the second case study, the distinction between film contamination and substrate material contamination is discussed. In this case the characterization of a ZnO film deposited on sapphire is presented. The concept of equivalent depth is discussed and it is shown to be an important tool for a straightforward distinction between film and bulk contamination. Copyright © 2005 John Wiley & Sons, Ltd.

InAs growth and development of defect microstructure on GaAs

Epitaxially deposited thin films of InAs on semi-insulating GaAs substrates are commonly used for high-speed electronic devices. Large (7%) lattice mismatch between InAs and GaAs leads to Stranski–Krastanov growth mode with formation of 3D islands. The effect of growth temperature in MOVPE deposition, on InAs crystal microstructure was studied. The origin of multiple tilting of the InAs crystal lattice observed for the high temperature growths was investigated in detail. The microstructure of uncoalesced InAs islands was determined using X-ray diffraction rocking curve scans and backscattered electron Kikuchi pattern crystal orientation imaging. Misoriented grains are formed within uncoalesced InAs islands at an early stage during the growth.

Growth and structural properties of thick InAs films on GaAs with low-pressure metalorganic vapor phase epitaxy

High quality InAs films are grown on GaAs (0 0 1) substrates by low-pressure metalorganic vapor phase epitaxy. It is found that the combination of InAs buffer grown under low temperature and InAs epilayer grown under high temperature is essential to obtain high quality InAs films. The role of buffer layer is discussed. AFM observation on thick InAs film surface shows that step-flow growth mode takes place. The crystalline quality of InAs is characterized by transmission electron microscopy and X-ray diffraction. The crystalline quality improves with increase in film thickness. Residual strain due to thermal mismatch between InAs layers and GaAs substrates is investigated with X-ray diffraction.

Formation of InAs/GaAs quantum dots by dewetting during cooling

We describe a method to form InAs quantum dots on GaAs by cooling an InAs film that is deposited at high substrate temperatures. The reflection high-energy electron diffraction pattern taken after deposition of 1.9 monolayers of InAs on (100) GaAs at 540 °C does not display the characteristic spot pattern that is seen when three-dimensional islands form on the surface. The characteristic spot pattern appears when the sample is cooled to about 330 °C, indicating that the three-dimensional islands appear at this temperature. Atomic force microscopy confirms the existence of the islands. An explanation for this behavior based on an increase in intermixing at the InAs/GaAs interface is proposed.

A Novel Approach for the Evaluation of Band Gap Energy in Semiconductors

On the basis of absorption nature of semiconductors, we present a novel and simple method to determine the band gap energies of semiconductors directly from their absorption spectra at any temperatures, without any fitting processes and restrictions of sample thickness. The key point of the approach is the different dependence of the absorption coefficient derivative on the photon energy at different absorption regions in semiconductors. We first demonstrate and verify the approach by detailed temperature-dependent absorption measurements, combined with photoluminescence measurements and empirical band gap equations for the direct band gap of uniform InAs films, and then extend successfully to the indirect band gap of elemental Ge and to the ternary HgCdTe alloys with composition gradient. Furthermore, we have also shown that our approach can not only evaluate the average band gap energy for ternary semiconductor alloys, but also estimate their composition uniformity to monitor the material quality.

Deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems: Theoretical calculations and experimental measurements

A comprehensive, quantitative analysis is presented of the deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems. The analysis combines a hierarchical theoretical approach with experimental measurements. Continuum linear elasticity theory is linked with atomic-scale calculations of structural relaxation for detailed theoretical studies of deformation in systems consisting of InAs thin films on thin GaAs(111)A substrates that are mechanically unconstrained at their bases. Molecular-beam epitaxy is used to grow very thin InAs films on both thick and thin GaAs buffer layers on epi-ready GaAs(111)A substrates. The deformation state of these samples is characterized by x-ray diffraction (XRD). The interplanar distances of thin GaAs buffer layers along the [220] and [111] crystallographic directions obtained from the corresponding XRD spectra indicate clearly that thin buffer layers deform parallel to the InAs/GaAs(111)A interfacial plane, thus aiding in the accommodation of the strain induced by lattice mismatch. The experimental measurements are in excellent agreement with the calculated lattice interplanar distances and the corresponding strain fields in the thin mechanically unconstrained substrates considered in the theoretical analysis. Therefore, this work contributes direct evidence in support of our earlier proposal that thin buffer layers in layer-by-layer semiconductor heteroepitaxy exhibit mechanical behavior similar to that of compliant substrates [see, e.g., B. Z. Nosho, L. A. Zepeda-Ruiz, R. I. Pelzel, W. H. Weinberg, and D. Maroudas, Appl. Phys. Lett. 75, 829 (1999)].

Correlation of defect profiles with carrier profiles of InAs epilayers on GaP

The carrier profile for InAs films grown on GaP is modeled as a first-order approximation which assumes that 90° edge dislocation intersections and the threading dislocation intersections act as shallow donors. Due to dislocation annihilation during growth, the threading dislocation intersection density decreases as the inverse of the distance x from the InAs/GaP interface, D(x)=D0x0/(x0+x), where D0 and x0 are dislocation density at the InAs/GaP interface and the first annihilation position from the interface, respectively. The carrier profile in InAs films can be described by a similar equation that is deduced from the threading dislocation intersection profile. The calculated carrier profiles agree well with measured carrier profiles. This correlation supports our hypothesis that both the edge dislocation intersections and the threading dislocation intersections act as shallow donor sources.

In situ observation of surface processes in InAs/GaAs(001) heteroepitaxy: The role of As on the growth mode

Surface processes of the growing thin films of InAs on GaAs(001) substrates have been studied as a function of substrate temperature and As to In flux ratio. They have been observed by reflection high-energy electron diffraction and total-reflection-angle x-ray spectroscopy in real time. At temperatures lower than ∼480 °C, InAs grows in a Stranski–Krastanov mode irrespective of the As/In flux ratio, while the growth mode of InAs strongly depends on the flux ratio above ∼500 °C. We have found that the sticking probability of In decreases as the As flux is decreased above ∼500 °C, which results in the changes in the growth mode of InAs.

ケルビンフォース法による表面電位測定技術の現状 ＫＦＭによるＧａＡｓ（１１０）面上ＩｎＡｓ薄膜表面のポテンシャル計測

Using Kelvin probe force microscopy (KFM), we have measured the surface potential of InAs thin films grown on flat or vicinal surfaces of GaAs(110) substrates. We found that the observed potential distribution corresponded to the surface corrugation of the InAs films and that the evaluated surface Fermi level position of the thick InAs was slightly closer to the vacuum level than that of the thin InAs. It was also found that the removal of the water-related contamination from both surfaces of the tip and the sample was very effective in order to improve the reliability of the potential measurements by KFM.