Growth and characterization of indium phosphide single-crystal nanoneedles on microcrystalline silicon surfaces

The epitaxial growth of nanometer-scale structures on non-single crystalline surfaces is proposed and demonstrated. Hydrogenated amorphous silicon was deposited onto an SiO₂ surface by plasma-enhanced chemical vapor deposition. Indium phosphide was deposited on the amorphous silicon by low-pressure metalorganic chemical vapor deposition in the presence of colloidal gold particles as catalysts. Under specific growth conditions, the indium phosphide formed nanoneedles connected to a microcrystalline silicon film nucleated within the amorphous silicon during the growth of the nanoneedles. Transmission electron microscopy revealed the presence of two different crystallographic structures: zinc-blende and wurtzite. Micro-photoluminescence measurements at room temperature showed two peaks with substantial blue-shifts with respect to that of bulk zinc-blende indium phosphide. PACS 81.16.Hc; 81.07.Vb; 68.65.La     

Characterization of chemically etched indium phosphide surfaces with light scattering

Scattering of light from chemically etched InP surfaces is studied in the present paper. A model is developed to describe the randomly rough surfaces produced by chemical etching and this model is used in a numerical simulation using the Kirchhoff approximation to calculate the scattered intensity distribution from the surfaces. Comparisons between the numerical results and experimental measurements for an incident wavelength of 633 nm show good agreement. Numerical simulation results are presented to show the variation of the scattered intensity distribution for surfaces with different times of chemical etching. These results are useful for characterization or control of this type of surface.     

Characterization of chemically etched indium phosphide surfaces with light scattering

Scattering of light from chemically etched InP surfaces is studied in the present paper. A model is developed to describe the randomly rough surfaces produced by chemical etching and this model is used in a numerical simulation using the Kirchhoff approximation to calculate the scattered intensity distribution from the surfaces. Comparisons between the numerical results and experimental measurements for an incident wavelength of 633 nm show good agreement. Numerical simulation results are presented to show the variation of the scattered intensity distribution for surfaces with different times of chemical etching. These results are useful for characterization or control of this type of surface.     

Low temperature adsorption of water on cleaved GaAs(110) surfaces

The adsorption and desorption of water on UHV-cleaved GaAs(110) surfaces was studied using synchrotron-excited photoelectron spectroscopy. Water was adsorbed at T = 100 K. Desorption was studied during heating to room temperature. At low coverages, dissociated species are observed followed by molecular adsorption. Molecular water is desorbed at T = 160 K. The dissociated species are also mainly desorbed after heating to room temperature. The chemical changes are accompanied by substrate binding-energy shifts, reflecting the movement of the Fermi level at the surface.     

Surface characterisation of indium phosphide

LEED, characteristic loss spectroscopy, Auger electron spectroscopy, photoemission and light modulated contact potential methods have been employed to study indium phosphide surfaces. Cleaved (110) faces have a surface unit mesh identical to that of the bulk and surface states lead to band bending in the surface region. Reaction with oxygen leads to loss of phosphorus and the formation of an oxide layer near the surface. Features in the characteristic loss spectrum are discussed in terms of interband transitions and plasmon losses and the Auger spectra of oxidized surfaces are thought to contain components due to cross transitions. The surface composition, band bending and photothresholds of etched (100) surfaces of epitaxial InP layers have been established. Surfaces cannot be cleaned by heat treatment alone since decomposition occurs at elevated temperature. The influence of evaporated silver on the sign of the surface photovoltage has also been investigated.     

Surface reactivity of oxygen on cleaved and sputtered graphite

The characterization of reactions which occur during the oxidation of highly oriented pyrolytic graphite (HOPG) was performed using high-resolution electron energy loss spectroscopy (HREELS) temperature programmed desorption (TPD), and scanning tunneling microscopy (STM). The results of this investigation provide spectroscopic evidence for the presence of semi-quinone functionalities on sputtered and oxidized HOPG STM images are presented to quantify the increase in defect sites after oxygen ion sputtering, and to correlate defect site density with reactivity.     

Free and bound exciton decay in indium phosphide

Excitonic recombination and photoconductivity near the energy gap of vapour grown InP epitaxial layers are investigated. Besides the free exciton several bound exciton complexes are observed and studied as a function of temperature. A new value of the band gap is derived (E_g = 1.424 ± 0.001 meV).     

Magnetic and optical properties of ytterbium-doped indium phosphide crystals

The intimate relation connecting the magnetic and optical properties of ytterbium-doped indium phosphide is studied under the conditions of local magnetic ordering and compensation of spin correlations by electron-vibration interaction. An analysis of the temperature dependences of the static magnetic susceptibility and photoluminescence spectra shows that the impurity magnetism of InP(Yb) crystals originates from the presence of antiferromagnetically ordered Yb₂O₃ quasi-molecules, which transfer to a ferromagnetically ordered state in the vicinity of shallow donors by capturing a donor electron or compete to form regions of local magnetic ordering (bound spin polarons). In both cases, the s-f exchange constants, as derived from the temperature dependences of the static magnetic susceptibility, are found to be anomalously large, apparently because of the spin correlations being efficiently compensated by electron-vibration interaction. In addition, due to the s-f exchange, an exchange-coupled deep level of the ferromagnetically ordered Yb₂O₃ quasi-molecule arises in the band gap of indium phosphide. The formation of this level simulates Auger recombination of nonequilibrium carriers, which is responsible for enhancement of the intracenter photoluminescence of Yb³⁺ ions.     

Spatial investigation of an iron-doped indium phosphide ingot

A whole Czochralski-grown iron-doped indium phosphide ingot was investigated by various techniques, all along the growth axis. Scanning photoluminescence, secondary ion mass spectroscopy and sheet resistance techniques were used. The average photoluminescence intensity and the iron concentration were found to be correlated. Samples of the ingot were annealed and implanted. For low ion-implantation doses, the electrical properties were mainly dependent on the initial properties of the ingot.     

AC surface photovoltage of indium phosphide nanowire networks

Surface photovoltage is used to study the dynamics of photogenerated carriers which are transported through a highly interconnected three-dimensional network of indium phosphide nanowires. Through the nanowire network charge transport is possible over distances far in excess of the nanowire lengths. Surface photovoltage was measured within a region 10.5?C14.5?mm from the focus of the illumination, which was chopped at a range of frequencies from 15 Hz to 30 kHz. Carrier dynamics were modeled by approximating the nanowire network as a thin film, then fitted to experiment suggesting diffusion of electrons and holes at approximately 75% of the bulk value in InP but with significantly reduced built-in fields, presumably due to screening by nanowire surfaces.     

Femtosecond laser micromachining of grooves in indium phosphide

Femtosecond laser micromachining of indium phosphide is investigated using 150 fs light pulses at a center wavelength of 800 nm. The ablation rate for micromachining of grooves is investigated as a function of pulse energy, feed rate, number of passes over the same groove, and the light polarization relative to the cutting direction. A logarithmic dependence of the groove depth on the laser fluence is observed with two regimes characterized by different ablation rates and different thresholds. The groove depth is found to be inversely proportional to the feed rate or equivalently linearly proportional to number of pulses delivered per unit area. With multiple passes over the same groove the depth increases linearly up to about 20 consecutive passes. Above 20 passes the ablation rate decreases until a depth limit is approached. The best results in terms of groove geometry and depth limit are obtained with the polarization of the beam perpendicular to the cutting direction. PACS 42.62.Cf; 79.20.Ds; 81.20.Wk     

Ultrashort-pulse laser ablation of indium phosphide in air

Ablation of indium phosphide wafers in air was performed with low repetition rate ultrashort laser pulses (130 fs, 10 Hz) of 800 nm wavelength. The relationships between the dimensions of the craters and the ablation parameters were analyzed. The ablation threshold fluence depends on the number of pulses applied to the same spot. The single-pulse ablation threshold value was estimated to be φ_th(1)=0.16 J/cm². The dependence of the threshold fluence on the number of laser pulses indicates an incubation effect. Morphological and chemical changes of the ablated regions were characterized by means of scanning electron microscopy and Auger electron spectroscopy. Received: 30 May 2000 / Accepted: 31 May 2000 / Published online: 23 August 2000     

Variations of work function and surface conductivity on clean cleaved zinc oxide surfaces by annealing and by hydrogen adsorption

Crystals are cleaved in UHV normal and parallel to the c axis exposing polar and prism faces. Work function (Kelvin) and surface conductivity are measured, also after annealing at elevated temperatures in UHV and after adsorption of atomic hydrogen. The work function of all three faces decreases irreversibly by annealing in UHV, but only on the Zn face a measurable surface conductivity appears. Also hydrogen adsorption diminuishes the work function. Simultaneously an increasing surface conductivity can be observed on all three types of surfaces. Corresponding structures in the annealing curves demonstrate a correlation between work function and surface conductivity. By means of space charge calculations band bending values are derived and there-by the electron affinity, which is not accessible to direct measurement. It is concluded that the two clean cleaved polar faces exhibit a depletion layer, which remains on the O face also after annealing in UHV. On the prism face nearly flat band situation is found. The decrease of work function with increasing hydrogen coverage, i.e. surface electron density, can be interpreted by means of space charge calculations using the measured surface conductivity. For the two polar faces the band bending alone causes the decrease, whereas for the prism face an additional increase of electron affinity has to be assumed. The variation of electron affinity by annealing or by hydrogen adsorption might be due to a change of atomic distances in the uppermost layer, although no superstructure has been found in LEED studies.     

Optical detection of magnetic resonance on anion antisites in indium phosphide

The paper describes the application of optically detected magnetic resonance (ODMR) methods to the identification of antisite defects in the III–V semiconductor InP. In III–V semiconductors the high abundance of nuclei with large nuclear spins greatly limits the resolution of magnetic resonance techniques. In particular, ODMR signals characteristic of the P_In antisite in InP with slightly differentg-values and hyperfine splitting have been observed. The corresponding centres cannot be distinguished with confidence without the higher resolution of electron-nuclear double resonance (ENDOR). Magnetic resonance signals of the antisite in InP are too weak to allow such measurements in the conventional detection mode, but using optically detected ENDOR (ODENDOR) in absorption as well as in emission, the isolated P_In antisite and at least one other antisite defect were identified. Moreover, the energy position of the P _In ⁺ /P _In ⁺⁺ level in the bandgap was determined from the optical transitions involved.     

Surface modifications by swift heavy-ion irradiation of indium phosphide

InP (001) samples were irradiated with 200 MeV Au ions at different fluences. The surface nanotopographical changes due to increasing fluence of swift heavy ions were observed by Atomic Force Microscopy (AFM), where the onset of a large increase in surface roughness for fluences sufficient to cause complete surface amorphization was observed. Transmission Electron Microscopy (TEM) was used to observe bulk-ion tracks that formed in InP, and high resolution TEM (HRTEM) revealed that single-ion tracks might not be amorphous in nature. Surface-ion tracks were observed by AFM in the form of ill-defined pits (hollows) of ~12 nm in diameter (width). In addition, Rutherford backscattering was utilized to follow the formation of disorder to amorphization in the irradiated material. The interpretation of the large increase in surface roughness with the onset of amorphization can be attributed to the plastic phenomena induced by the change of states from crystalline to amorphous by ion irradiation. The text was submitted by the authors in English.     

Free and bound electron transitions to acceptors in indium phosphide

In epitaxial InP a new emission band at 1.3776 eV is identified as the free electron-acceptor transition. It is investigated in connection with the corresponding donor-acceptor pair band at 1.374 eV. This permits an individual determination of the acceptor and donor binding energies (48 ± 1 meV and 7.3 ± 0.6 meV respectively). A second new emission band at 1.396 eV is reported and discussed.