InAs Surface Research Articles

Competing nucleation mechanisms and growth of InAsSbP quantum dots and nano-pits on the InAs(100) surface

InAsSbP quantum dots (QDs) and nano-pits (NPs) are grown on a InAs(100) surface by liquid phase epitaxy (LPE). Their morphology, dimensions and distribution density are investigated by high resolution scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and total energy calculations. QDs average density ranges from 5 to 7 × 10 9 cm − 2, with heights and widths having a Gaussian distribution with sizes from 5 nm to 15 nm and 10 nm to 40 nm respectively. The average pits density is (2–6) × 10 10 cm − 2 with dimensions ranging from 5–30 nm in width and depth. We also find a shift in the absorption edge towards the longer wavelengths together with broadening towards shorter wavelengths indicating that these QDs and lateral overgrown nano-pits are grown at the n-InAs/p-InAsSbP heterojunction interface. Together with total energy calculations, the results indicate that lattice mismatch ratio plays a central role in the growth of these strain-induced nano-objects.

Native oxides and carbon contamination removal from InAs(100) surface by molecular hydrogen flow at moderate substrate temperatures: Stoichiometric and morphological studies

Native oxides and carbonaceous contamination removal from InAs(100) surfaces by thermal annealing at reduced temperatures under molecular hydrogen flow is reported and compared to vacuum annealing at similar temperatures. The thermal annealing experiments were carried out in the 250–360 °C range and at constant hydrogen pressure of 5×10−6 torr. The complete reduction of native oxides and carbon contamination was achieved at temperatures as low as 300 and 340 °C, respectively, under molecular hydrogen flux. Chemical and compositional monitoring of the surface was performed by x-ray photoelectron spectroscopy and x-ray induced Auger spectroscopy. The surface morphology, before and after annealing, was imaged by atomic force microscope at tapping noncontact mode.

Composition, morphology and surface recombination rate of HCl–isopropanol treated and vacuum annealed InAs(1 1 1)A surfaces

X-ray photoelectron spectroscopy and atomic force microscopy were used to examine the chemical composition and surface morphology of InAs(1 1 1)A surface chemically etched in isopropanol–hydrochloric acid solution (HCl–iPA) and subsequently annealed in vacuum in the temperature range 200–500 °C. Etching for 2–30 min resulted in the formation of “pits” and “hillocks” on the sample surface, respectively 1–2 nm deep and high, with lateral dimensions 50–100 nm. The observed local formations, whose density was up to 3 × 10 8 cm −2, entirely vanished from the surface after the samples were vacuum-annealed at temperatures above 300 °C. Using a direct method, electron beam microanalysis, we have determined that the defects of the hillock type includes oxygen and excessive As, while the “pits” proved to be identical in their chemical composition to InAs. Vacuum anneals were found to cause a decrease in As surface concentration relative to In on InAs surface, with a concomitant rise of surface recombination rate.

Preparation of As‐rich (2x4) – III‐As (001) surfaces by wet chemical treatment and vacuum annealing

AbstractThe GaAs and InAs (001) surfaces chemically treated in HCl‐isopropanol solution (HCl‐iPA) and annealed in vacuum were studied by means of photoemission, low energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS). The photoemission results demonstrated that the chemical treatment removed native oxides from Ga(In)As surfaces and yielded As‐rich surface with several monolayers of excess arsenic and small amounts of GaClx (InClx). Annealing at relatively low‐temperatures induced desorption of this overlayer and revealed a clean arsenic‐rich (2x4)/c (2x8) structure on GaAs and InAs(100) surfaces. The structural properties of chemically prepared III‐As (001) surfaces were found to be similar to those obtained by decapping of As‐capped epitaxial layers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Core-level shifts of the c(8 × 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) surfaces

We have studied In-stabilized c(8 × 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III–V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the ζ and ζa models, which have been previously established to describe the atomic structures of the III–V(1 0 0) c(8 × 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III–V(1 0 0) c(8 × 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated ζ and ζa SCLS values shows that the InSb spectra are reproduced by the ζ SCLSs better than by the ζa SCLSs. Interestingly, the ζa fits agree better with the InAs spectra than the ζ fits do, indicating that the ζa model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III–V(1 0 0) c(8 × 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges.

Excitation Wavelength Dependence of Terahertz Radiation from InAs: UV versus IR

Terahertz (THz) radiation measurements from p-doped InAs (carrier density: ∼ 7 × 10 cm−3) surfaces were carried out encompassing both IR (770–830 nm) and UV (360–385 nm) excitations by employing two synchronized femtosecond lasers. Each laser was independently tunable, and the jitter was controlled below the pulse width (∼150 fs). One laser was used for THz generation, and the other for detection via a photoconductive antenna. For the IR-pulse excitation, two frequency components were observed, between which the higher-side peak disappeared as we tuned the excitation wavelength toward the UV range.

Functionalized Self-Assembled InAs/GaAs Quantum-Dot Structures Hybridized with Organic Molecules

Low-dimensional III–V semiconductors have many advantages over other semiconductors; however, they are not particularly stable under physiological conditions. Hybridizing biocompatible organic molecules with advanced optical and electronic semiconductor devices based on quantum dots (QDs) and quantum wires could provide an efficient solution to realize stress-free and nontoxic interfaces to attach larger functional biomolecules. Monitoring the modifications of the optical properties of the hybrid molecule–QD systems by grafting various types of air-stable diazonium salts onto the QD structures surfaces provides a direct approach to prove the above concepts. The InAs/GaAs QD structures used in this work consist of a layer of surface InAs QDs and a layer of buried InAs QDs embedded in a wider-bandgap GaAs matrix. An enhancement in photoluminescence intensity by a factor of 3.3 from the buried QDs is achieved owing to the efficient elimination of the dangling bonds on the surface of the structures and to the decrease in non-radiative recombination caused by their surface states. Furthermore, a narrow photoluminescence band peaking at 1620 nm with a linewidth of 49 meV corresponding to the eigenstates interband transition of the surface InAs QDs is for the first time clearly observed at room temperature, which is something that has rarely been achieved without the use of such engineered surfaces. The experimental results demonstrate that the hybrid molecule–QD systems possess a high stability, and both the surface and buried QDs are very sensitive to changes in their surficial conditions, indicating that they are excellent candidates as basic sensing elements for novel biosensor applications.

Intense interface luminescence in type II narrow-gap InAs-based heterostructures at room temperature

Positive and negative luminescence was observed in a type II broken-gap p-InAs/p-GaAsSb heterostructure in the mid-infrared spectral range 3–5 μm at room temperature. Interface-related radiative recombination was provided by Mn acceptor states on InAs surface. I–V characteristics behavior was discussed using the tunneling-assisted current transport mechanism through surface states. Redistribution between the interband (hv1=0.36eV) and interface (hv2=0.31eV) emission bands in electroluminescent spectra at reverse bias was found in dependence on Fermi level position pinning by surface states at the type II broken-gap heterointerface.

10.1007/s11453-008-1010-4

Formation of InSb quantum dots grown in an InAs matrix by molecular-beam epitaxy that does not involve forced deposition of InSb is studied. Detection of intensity oscillations in the reflection of high-energy electron diffraction patterns was used to study in situ the kinetics of the formation of InSb quantum dots and an InAsSb wetting layer. The effects of the substrate temperature, the shutter operation sequence, and the introduction of growth interruptions on the properties of the array of InSb quantum dots are examined. Introduction of a growth interruption immediately after completing the exposure of the InAs surface to the antimony flux leads to a reduction in the nominal thickness of InSb and to an enhancement in the uniformity of the quantum-dot array. It is shown that, in the case of deposition of submonolayer-thickness InSb/InAs quantum dots, the segregation layer of InAsSb plays the role of the wetting layer. The Sb segregation length and segregation ratio, as well as their temperature dependences, are determined.

Resonant tunneling of electrons through single self-assembled InAs quantum dot studied by conductive atomic force microscopy

Resonant tunneling of electrons through a quantum level in single self-assembled InAs quantum dot (QD) embedded in thin AlAs barriers has been studied. The embedded InAs QDs are sandwiched by 1.7-nm-thick AlAs barriers, and surface InAs QDs, which are deposited on 8.3 nm-thick GaAs cap layer, are used as nano-scale electrodes. Since the surface InAs QD should be vertically aligned with a buried one, a current flowing via the buried QD can be measured with a conductive tip of an atomic force microscope (AFM) brought in contact with the surface QD-electrode. Negative differential resistance attributed to electron resonant tunneling through a quantized energy level in the buried QD is observed in the current–voltage characteristics at room temperature. The effect of Fermi level pinning around nano-scale QD-electrode on resonance voltage and the dependence of resonance voltage on the size of QD-electrodes are investigated, and it has been demonstrated that the distribution of the resonance voltages reflects the size variation of the embedded QDs.

Making Mn Substitutional Impurities in InAs using a Scanning Tunneling Microscope

We describe in detail an atom-by-atom exchange manipulation technique using a scanning tunneling microscope probe. As-deposited Mn adatoms (Mn(ad)) are exchanged one-by-one with surface In atoms (In(su)) to create a Mn surface-substitutional (Mn(In)) and an exchanged In adatom (In(ad)) by an electron tunneling induced reaction Mn(ad) + In(su) --> Mn(In) + In(ad) on the InAs(110) surface. In combination with density-functional theory and high resolution scanning tunneling microscopy imaging, we have identified the reaction pathway for the Mn and In atom exchange.

Anomalous hybridization in the In-rich InAs(0 0 1) reconstruction

The surface bonding arrangement in nearly all the confirmed reconstructions of InAs(0 0 1) and GaAs(0 0 1) have only two types of hybridization present. Either the bonds are similar to those in the bulk and the surface atoms are sp 3 hybridized or the surface atoms are in a tricoordinated bonding arrangement and are sp 2 hybridized. However, dicoordinated In atoms with sp hybridization are observed on the InAs(0 0 1), In-rich, room temperature and low temperature surfaces. Scanning tunneling microscopy (STM) images of the room temperature (300 K) InAs(0 0 1) surface reveal that the In-rich surface reconstruction consists of single-atom rows with areas of high electron density that are separated by ∼4.3 Å. The separation in electron density is consistent with rows of undimerized, sp hybridized, In atoms, denoted as the β3′(4 × 2) reconstruction. As the sample is cooled to 77 K, the reconstruction spontaneously changes. STM images of the low temperature surface reveal that the areas of high electron density are no longer separated by ∼4.3 Å but instead by ∼17 Å. In addition, the LEED pattern changes from a (4 × 2) pattern to a (4 × 4) pattern at 77 K. The 77 K reconstruction is consistent with two (4 × 2) subunit cells; one that contains In dimers on the row and another subunit cell that contains undimerized, sp hybridized, In atoms on the row. This combination of dimerized and undimerized subunit cells results in a new unit cell with (4 × 4) periodicity, denoted as the β3(4 × 4) reconstruction. Density functional theory (DFT) and STM simulations were used to confirm the experimental findings.

Self-Assembled Monolayers of Alkanethiols on InAs

We describe the deposition and properties of self-assembled monolayers (SAMs) of methyl-terminated alkanethiols on InAs(001) surface. For these model hydrophobic films, we used water contact angle measurements to survey the preparation of alkanethiol monolayers from base-activated ethanolic solutions as a function of the solution and deposition parameters, including chain length of alkanethiols, deposition time, and solution temperature and pH. We then used X-ray photoelectron spectroscopy (XPS), ellipsometry, and electrochemistry to characterize the composition and structure of octadecanethiol (ODT) monolayers deposited on InAs under optimized conditions. When applied to a thoroughly degreased InAs(001) wafer surface, the basic ODT solution removes the native oxide without excessively etching the underlying InAs(001) substrate. The resulting film contains approximately one monolayer of ODT molecules, attached to the InAs surface almost exclusively via thiolate bonds to In atoms, with organic chains extended away from the surface. These ODT monolayers are stable against degradation and oxidation in air, organic solvents, and aqueous buffers. The same base-activated ODT treatment can also be used to passivate exposed InAs/AlSb quantum well (QW) devices, preserving the unique electronic properties of InAs surfaces and allowing the operation of such passivated devices as continuous flow pH-sensors.

Density-functional calculations for self-assembled Bi-nanolines on the InAs(100) surface

We have performed an ab initio investigation of the stability, atomic geometry, and electronic properties of the self-assembled bismuth (Bi)-nanolines on the Bi-stabilized indium arsenide (InAs)(100) surface. Our calculations were performed within the local density approximation of the density functional theory, using pseudopotentials to describe the electron-ion interactions. We have examined several metastable Bi nanolines arrangements on the top of the Bi-stabilized InAs(100) surface. Our total energy calculations suggest that the most stable configuration of the Bi nanolines is formed by Bi dimers parallel to the Bi dimers on the Bi/InAs(100) surface. We have found that the structure is metallic with several occupied and unoccupied surface states within the bulk InAs gap region. These states are mainly due to the top and first sublayer Bi atoms. Our theoretically simulated scanning tunneling microscope (STM) image shows a very bright line along the [01¯1] direction, which is consistent with the experimental STM images.

Etching and oxidation of InAs in planar inductively coupled plasma

The surface of InAs (1 1 1)A was investigated under plasmachemical etching in the gas mixture CH 4/H 2/Ar. Etching was performed using the RF (13.56 MHz) and ICP plasma with the power 30–150 and 50–300 W, respectively; gas pressure in the reactor was 3–10 mTorr. It was demonstrated that the composition of the subsurface layer less than 5 nm thick changes during plasmachemical etching. A method of deep etching of InAs involving ICP plasma and hydrocarbon based chemistry providing the conservation of the surface relief is proposed. Optimal conditions and the composition of the gas phase for plasmachemical etching ensuring acceptable etch rates were selected.

Specific features of the epitaxial growth of narrow-gap InSb quantum dots on an InAs substrate

Arrays of coherent InSb quantum dots (QDs) have been fabricated by liquid-phase epitaxy on InAs substrates in the temperature range T = 420–450°C. The QDs with a density of (0.9−2) × 1010 cm−2 were 3 nm high and 13 nm in diameter. A bimodal QD size distribution was observed, which was accounted for by a combined growth mechanism of these nanoobjects. Structural characteristics of a separate InSb QD formed on the InAs surface were studied for the first time by atomic-force and transmission electron microscopies. Moire fringes were observed for the first time for QDs in the InSb/InAs system, with the moire period of 3.5 nm corresponding to InSb QDs without an admixture of arsenic.

Sulfide passivation of InAs(100) substrates in Na2S solutions

Treatment of the InAs(100) surface with a 1M aqueous solution of sodium sulfide (Na2S) is found to result in the removal of a natural oxide layer from this surface with the formation of a continuous chemisorbed passivating layer of sulfur atoms that are coherently bonded to indium atoms of the crystal surface. No etching of the InAs surface in the sulfide solution occurs. The passivated InAs samples are characterized by a multiple increase in the photoluminescence intensity. The sulfide layer is desorbed from the InAs surface at temperatures of ∼400°C. This leads to the formation of a clean In-stabilized (100) surface with a (4 × 2) reconstruction. A simple technique is developed using sulfide passivation for preparing atomically smooth (2 × 4) growth surfaces of the InAs(100) substrates that are suitable for molecular-beam epitaxy of highly perfect layers of compounds based on CdSe.

Terahertz pulse emission from semiconductor surfaces illuminated by femtosecond Yb:KGW laser pulses

Abstract The amplitudes of terahertz pulses emitted from the surfaces of InAs, InSb, InGaAs, GaAs and Ge after their excitation by femtosecond 1 μm laser pulses was compared. It has been found that this effect is most efficient in p-type InAs. The mechanisms leading to the terahertz emission are investigated and discussed. It has been concluded that in the majority of the investigated semiconductors the main contribution to THz pulse emission comes from the electrical-field-induced optical rectification effect.

Initial stages of the autocatalytic oxidation of the InAs(0 0 1)-(4 × 2)/ c(8 × 2) surface by molecular oxygen

The initial stages of oxidation of the In-rich InAs(0 0 1)-(4 × 2)/ c(8 × 2) surface by molecular oxygen (O 2) were studied using scanning tunneling microscopy (STM) and density functional theory (DFT). It was shown that the O 2 dissociatively chemisorbs along the rows in the [1 1 0] direction on the InAs surface either by displacing the row-edge As atoms or by inserting between In atoms on the rows. The dissociative chemisorption is consistent with being autocatalytic: there is a high tendency to form oxygen chemisorption sites which grow in length along the rows in the [1 1 0] direction at preexisting oxygen chemisorption sites. The most common site size is about 21–24 Å in length at ∼25% ML coverage, representing 2–3 unit cell lengths in the [1 1 0] direction (the length of ∼5–6 In atoms on the row). The autocatalysis was confirmed by modeling the site distribution as non-Poisson. The autocatalysis and the low sticking probability (∼10 −4) of O 2 on the InAs(0 0 1)-(4 × 2)/ c(8 × 2) are consistent with activated dissociative chemisorption. The results show that is it critical to protect the InAs surface from oxygen during subsequent atomic layer deposition (ALD) or molecular beam epitaxy (MBE) oxide growth since oxygen will displace As atoms.

Spatially resolved low-frequency noise measured by atomic force microscopy

We report spatially resolved charge noise measurements on semiconductor samples by atomic force microscopy. We observed charge noise induced by light illumination on an InP/InGaAs heterostructure with surface InAs quantum dots and a buried two-dimensional electron gas. The observed noise exhibits generation-recombination noise or random telegraph noise depending on light intensity and bias voltage. A spatial resolution better than 20 nm was demonstrated by comparing the noise on and off the InAs quantum dots. The approach enables the localization of individual traps and will aid in understanding noise mechanisms.