No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Spectroscopic studies of compound semiconductor surfaces as it relates to the growth of nanomaterials
Abstract
The structure of indium phosphide surfaces and interfaces has been investigated during the growth of nanomaterials by metalorganic chemical vapor deposition. In the phosphorus-rich environment of the MOCVD process, the InP (001) surface forms a (2x1) reconstruction that is terminated with a monolayer of phosphorus dimers. Each of these dimers is stabilized by the adsorption of hydrogen onto one of the dangling bonds. Upon switching from the growth of InP to InGaAs or InSb, the surface can change dramatically depending on the interactions among the group V elements. When InP is exposed to tertiarybutylarsine above 500 °C, arsenic atoms diffuse into the bulk, creating strained InAsP films with a roughness exceeding 1.0 nm. By contrast, when InP is exposed to trimethylantimony between 450 and 600 °C, a thin layer of InSb, ~6.8 Å thick, is deposited. This layer is strained in only one direction, and forms an interesting one-dimensional, ridge-shaped structure.
ResearchGate has not been able to resolve any citations for this publication.
The stability of different surface reconstructions on InAs(001) is investigated theoretically and experimentally. Density-functional theory calculations predict four different surface reconstructions to be stable at different chemical potentials. The two dominant reconstructions are the beta 2 (2x4) for high As, and the alpha 2 (2x4) for low As overpressure. This trend is confirmed by scanning tunneling microscopy of carefully annealed InAs(001) surfaces. A similar behavior is predicted for GaAs(001).
Hydrogen adsorption on the InP (001)-(21) reconstruction has been characterized by vibrational spec-troscopy and ab initio calculations with density functional theory. The (21) surface is covered with a complete layer of phosphorus dimers. The clean and hydrogen-terminated dimers have been modeled by In 5 P 4 H x clusters with the proper number of covalent and dative bonds to accurately represent the surface of interest. The optimized molecular cluster of the unreacted dimer reveals that it has one filled and one partially filled dangling bond. Hydrogen atoms attack the P-P dimers forming terminal and coupled phosphorus-hydrogen bonds, and the predicted vibrational frequencies of these species are in excellent agreement with the infrared spectra. All the observed vibrational modes can be assigned to species containing one, two, and three hydrogen bonds i.e., PH, HP-PH, and PHPH 2 per surface dimer.
Scanning tunneling microscope (STM) images together with reflection high-energy electron diffraction (RHEED) showed for the first time convincingly that the molecular-beam epitaxially grown GaAs (001)-(2×4) alpha, beta, and gamma phases all have the same outermost surface layer of the unit cell: which consists of two As dimers and two dimer vacancies. Based on the STM and RHEED observations and dynamical RHEED calculation, a structure model consistent with various observations is proposed.
The InP(001)(2 x 1) surface has been reported to consist of a semiconducting monolayer of buckled phosphorus dimers. This apparent violation of the electron counting principle was explained by effects of strong electron correlation. Combining first-principles calculations with reflectance anisotropy spectroscopy and LEED experiments, we find that the (2 x 1) reconstruction is not at all a clean surface: it is induced by hydrogen adsorbed in an alternating sequence on the buckled P dimers. Thus, the microscopic structure of the InP growth plane relevant to standard gas phase epitaxy conditions is resolved and shown to obey the electron counting rule.
An InP(001)- \(2×1\) reconstruction was prepared by metal-organic
vapor-phase epitaxy. Scanning tunneling micrographs and infrared spectra
of adsorbed hydrogen revealed that the \(2×1\) is terminated with
a complete layer of buckled phosphorous dimers, giving rise to
p\(2×2\) and c\(4×2\) domains. A surface band gap of
1.2+/-0.2 eV was measured by scanning tunneling spectroscopy. The
buckling can be explained by electron correlation among the dangling
bonds of pairs of phosphorous dimers. This allows the surface to achieve
a lower energy, semiconducting state. This reconstruction mimics the
Si(100)- \(2×1\), which is terminated with buckled silicon dimers.
The present status and future prospects of compound semiconductor quantum nanostructures for sensing terahertz (THz) signals are reviewed. Various THz detectors reported in recent publications are reviewed first. They include infrared photodetectors based on quantum wells, superlattices and quantum dots, resonant tunneling diodes, single electron transistors and plasma resonators using high mobility electron transistor structures. Then, a novel approach by the authors utilizing planar arrays of quantum dots controlled by nano-scale Schottky wrap gates is presented and discussed. It is based on photon assisted resonant tunneling of single electrons. The novel device structure allows normal incidence of THz radiation as well as high density planar integration. A large responsivity of 0.3 A/W was obtained at 20 K for 2.5 THz laser beam.
In this letter, we present the results of InAs quantum dots (QDs) prepared on a (001) InP substrate. As/P exchange reaction at the surface of InP buffer was used to form the InAs islands in the reactor of low pressure metalorganic chemical vapor deposition at 600 °C. Preliminary characterizations of the InAs QDs have been investigated by using atomic force microscopy and photoluminescence (PL). Room temperature PL emission from the 0-dimensional system centers at 1520 nm and the full width at half maximum of the PL is 92 meV.
In InGaAs/InP heterostructures, interdiffusion of arsenic and phosphorus at the hetero-interfaces during epitaxial growth degrades the interface abruptness. This is a serious problem when a very thin InGaAs/InP quantum well is required. In this paper, spectroscopic and kinetic ellipsometry are used to monitor the As-P exchange in-situ in metal-organic vapor phase epitaxy (MOVPE) with TBAs and TBP as the group V precursors. As a result, it is found that the monitoring of As-P exchange is possible by kinetic ellipsometry and that useful information for improving the gas switching sequence is acquired from such observations. Information from this in-situ kinetic ellipsometry has been confirmed to agree well with ex-situ photoluminescence and transmission electron microscope (TEM) observations.
A phosphorous-rich structure is generated on the InP (001) surface during metalorganic vapor-phase epitaxy. It consists of phosphorous dimers, alkyl groups, and hydrogen atoms adsorbed onto a layer of phosphorous atoms. The adsorbed dimers produce c(2×2) and p(2×2) domains, with total phosphorous coverages of 2.0 and 1.5 ML. The alkyl groups and hydrogen atoms adsorb onto half of the exposed phosphorous atoms in the first layer. These atoms dimerize producing a (2×1) structure. It is proposed that the first layer of phosphorous atoms is the active site for the deposition reaction, and that the organometallic precursors compete with phosphorous dimers, alkyl radicals, and hydrogen for these sites during growth.
The surface structure of the indium phosphide (001)-(2×1) reconstruction has been clarified in this work. Infrared spectra collected during atomic deuterium titration of the InP (001)-(2×1) surface reveal a sharp P-H stretching mode at 2308 cm-1. Based on theoretical cluster calculations using density-functional theory, this mode results from a single hydrogen atom bonded to one end of a buckled phosphorus dimer. These results confirm that the (2×1) structure is hydrogen stabilized as recently proposed in the literature.
Some aspects of the morphology of InAs island formation on InP have been studied by atomic force microscopy, photoluminescence, photoluminescence excitation spectroscopy, and Raman scattering. The InAs layer is grown by chemical beam epitaxy on top of InP surfaces with sawtooth-like channels. The deposition of a thin InAs layer results in quantum dots strongly aligned along the InP channels. Subsequent annealing in an arsenic atmosphere produces growth and loss of coherency of the islands. Atomic force microscopy shows the changes in size and alignment of the islands. Optical measurements serve to give quantitative estimates of the strain distribution among the top of the InP buffer layer, the wetting layer and the islands for the differently treated samples. © 2000 American Institute of Physics.
We review the recent progress of GaN-based light emitting diodes (LEDs) and laser diodes (LDs) and discuss the availability for ultraviolet (UV) emission optoelectronic devices by using GaN related compound semiconductors. We fabricated UV LEDs and LDs with an emission wavelength of 365 nm which are useful for various industrial uses because of same wavelength as i-line of high-pressure mercury vapor lamps. Regarding UV LEDs, practical 365 nm UV LED with high efficiency was realized by optimizing device structure. For fabricating the ultraviolet LDs, we used the AlInGaN active layer instead of InGaN one. It was investigated that the relationship between the threshold current density and the lasing wavelength in the UV region. We demonstrated the shortest LDs with a lasing wavelength 365 nm under the continuous-wave operation. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
We have studied the initial stages of heterojunction formation during the metalorganic vapor-phase epitaxy of indium arsenide on indium phosphide. Exposing an InP 001 film to 10 mTorr of tertiarybutylarsine below 500 °C results in the deposition of a thin InAs layer from 1.5 to 5.0 atomic layers thick 2.3–7.5 Å. The surface of this epilayer remains atomically smooth independent of arsenic exposure time. However, in an overpressure of tertiarybutylarsine at or above 500 °C, the arsenic atoms diffuse into the bulk, creating strained InAsP films. These films form three-dimensional island structures to relieve the built-up strain. The activation energy and pre-exponential factor for arsenic diffusion into indium phosphide have been determined to be E d 1.70.2 eV and D o 2.31.010 7 cm 2 /s.
Indium phosphide 001 surfaces were exposed to 0.61-mTorr trimethylantimony in a metalorganic vapor-phase epitaxy reactor. The antimony surface composition increased rapidly with dosage and saturated at 22.0 at. % for temperatures between 450 and 600 ° C. The results indicate that a thin layer of InSb formed on the surface, 6.8 Å thick. Strain from the lattice mismatch caused faceting in the 110 direction, whereas the formation of Sb dimer bonds relieved the strain in the −110 direction. As a result, narrow ridges formed that ranged from 4 to 10 nm wide and from 3.0 to 18.0 Å high, depending on the antimony coverage. © 2005 American Institute of Physics.
The atomic structure of the InP001 reconstructions has been identified by scanning tunneling microscopy and infrared spectroscopy of adsorbed hydrogen. The four phases, in order of decreasing phosphorous cover-age, are c(22)/p(22), P 2.0 ML; (21), P 1.0 ML; (24), P 0.25 ML, and (24), P 0.125 ML. The (22) consists of phosphorous dimers adsorbed onto a layer of P atoms. Removal of the P adatoms at 300 °C, produces the (21), which is terminated with a complete layer of buckled phosphorous dimers. Further annealing at 400 to 500 °C, yields the indium-rich (24) and (24) reconstructions. The (24) reconstruction comprises a single phosphorous dimer in the top layer and four indium dimers in the second layer. The (24) differs from the (24) reconstruction in that one of the P atoms is replaced with an In atom to make an In-P heterodimer. This difference is evident by comparison of the intensities of P-H, In-H, and In-H-In stretching vibrations for the two surfaces.
Arsenic adsorption and exchange with phosphorus on indium phosphide 001 have been studied by scan-ning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron spectroscopy. The surface phase diagram as a function of temperature has been obtained. At 285 °C, arsenic adsorbs on the InP (24) surface (P coverage0.25 ML), forming a disordered (14) with double layers of arsenic (As P coverage 1.5 ML). At 330 °C, arsenic adsorbs on the (24), producing a (21) structure with a complete monolayer of group-V dimers. By contrast, some phosphorus desorption occurs above 350 °C, al-lowing arsenic to displace the phosphorus in the top few layers and converting the (24) to the 2 and 2(24) reconstructions As coverage 0.75 and 0.50 ML, respectively. Above 430 °C, arsenic exchange with InP yields an InAs (42) reconstruction. Quantitative analysis of the x-ray photoemission spectra has re-vealed that substitution of arsenic for phosphorus is limited to the top two to three surface bilayers.
The properties of Sb-based III-V semiconductor compounds for optoelectronic applications in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) range were reviewed. The growths of the Sb-based binary, ternary and quaternary were studied by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). The structural, optical and electrical characterizations were carried out. Focal plane array, photoconductors and photodiodes were fabricated for the MWIR and LWIR range. Doublehetero structure (DH), multi-quantum well (MQW) and strained superlattice (SSL) lasers in the 3–5 $\mu$m range were fabricated. InAs-GaSb type-II superlattices were designed, grown and fabricated into photodetectors for the MWIR and LWIR range.
The principal reconstructions found on the low-index planes of GaAs and ZnSe can be explained in terms of a simple electron counting model. A surface structure satisfies this model if it is possible to have all the dangling bonds on the electropositive element (Ga or Zn) empty and the dangling bonds on the electronegative element (As or Se) full, given the number of available electrons. This condition will necessarily result in there being no net surface charge. The justification for this model is discussed. The GaAs(001)-(2×4) reconstruction is known to involve surface dimers. It is shown that a (2×4) unit cell with three dimers and one dimer vacancy is the smallest unit cell that satisfies the electron counting model for this surface. The electron counting model is used to explain the structure of islands imaged by scanning tunneling microscopy on the GaAs(001)-(2×4) surface. The model shows that island structures built up from complete (2×4) unit cells can be stable if they extend in the 2× direction, but not if they extend in the 4× direction. These island structures can also provide an explanation for the different step structures seen on GaAs(001) vicinal surfaces. Much less is known experimentally about step and island structures on ZnSe(001). Structures on this surface predicted by the electron counting model differ significantly from those found on GaAs(001).
InAs/GaSb superlattices are studied in cross section by scanning tunneling microscopy and spectroscopy. Electron subbands in 42 Å thick InAs layers are clearly resolved in the spectra. Roughness of the superlattice interfaces is quantitatively measured. Interfaces of InAs grown on GaSb are found to be rougher, with different electronic properties, than those of GaSb on InAs, indicating some intermixing in the former case.
This paper reviews some of our pioneering contributions to the
field of III-V compound semiconductor materials and low-dimensional
optoelectronic devices. These contributions span from the ultraviolet
(λ~200 nm) up to the far-infrared (λ~25 μm) portion of
the electromagnetic spectrum and have had a major scientific and
technological impact on the semiconductor world in the past 20 years