In situ measurements of InAs and InP (0 0 1) surface stress changes induced by surface reconstruction transitions

The anisotropic surface stress changes associated with the transition between different surface reconstructions of InAs and InP (0 0 1) surfaces are measured in situ and in real time in a molecular beam epitaxy (MBE) system. Reflectivity anisotropy of the surface measured at 1.96 eV, together with reflection high energy electron diffraction (RHEED) pattern, are used in order to identify the surface reconstructions, and the monitoring of the substrate curvature evolution to determine the variations in surface stress. Our results show the important contribution to the surface stress of the dimers present in these reconstructed surfaces. Furthermore, we provide for the first time quantitative values of the surface stress changes due to the transition between surface reconstructions for these III-V semiconductors compounds. We obtain values for these changes up to 0.7 Nm⁻¹, that is, of the same magnitude as the stress induced by deposition of one monolayer during growth of lattice-mismatched III-V semiconductor heteroepitaxial systems. This points out the great importance of surface stress evolution in this kind of processes.     

Surface structure investigations using noncontact atomic force microscopy

Surfaces of several A_IIIB_V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination.     

AES, EELS and TRIM investigation of InSb and InP compounds subjected to Ar ions bombardment

The interaction of ions with matter plays an important role in the treatment of material surfaces. In this paper we study the effect of argon ion bombardment on the InSb surface in comparison with the InP one. The Ar⁺ ions, accelerated at low energy (300 eV) lead to compositional and structural changes in InP and InSb compounds. The InP surface is more sensitive to Ar⁺ ions than that of InSb. These results are directly inferred from the qualitative Auger electron spectra (AES) and electron energy loss spectroscopy (EELS) analysis. However, these techniques alone do not allow us to determine with accuracy the disturbed depth in Ar⁺ ions of InP and InSb compounds. For this reason, we combine AES and EELS with the simulation method TRIM (transport and range of ions in matter) to show the mechanism of interaction between the ions and the InP or InSb and hence determine the disturbed depth as a function of Ar⁺ energy.     

Calculation of distribution coefficients of donors in III-V semiconductors

The techniques recently developed for the calculation of III-V ternary phase diagrams have been extended to the calculation of distribution coefficients of impurities in III-V semiconductors. The distribution coefficients are calculated with no adjustable parameters, the calculation requiring only the temperatures and entropies of fusion, binary phase diagrams and lattice parameters of the relevant III-V compounds, and the tetrahedral covalent radii, electronegativities, molar volumes and atomization energies of the donor impurities and group III and V elements concerned.The calculation is carried out for common donors S, Se, Te and Sn at the melting points of the III-V compounds GaP, GaAs, GaSb, InP, InAs and InSb, and the results compared with experimental results where available. In GaAs and GaP, the distribution coefficients are calculated vs temperature for solidification from the group III rich melt.     

“Antisite” incorporation of Sb dopant in GaN

Radioactive ¹¹⁹Sb was implanted in an undoped GaN single crystal and Mössbauer spectra were taken of the 23.8 keV gamma rays of ¹¹⁹Sn emitted in its decay. A comparison with Mössbauer spectra of ¹¹⁹Sb implantated in other III-V compounds leads to the conclusion that Sb in GaN lands in the Ga site in contrast to all common III-V compounds, where Sb occupies the anion site. Calculations of electronegativity differences for Sb incorporation in either Ga or N site support our interpretation of the experimental data.     

Analysis of intensities of positive and negative ion species from silicon dioxide films using time-of-flight secondary ion mass spectrometry and electronegativity of fragments

Intensities of positive and negative ion species emitted from thermally oxidized and plasma-enhanced chemical vapor deposited (PECVD) SiO₂ films were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and the Saha-Boltzmann equation. Intensities of positive and negative secondary ion species were normalized to those of ²⁸Si⁺ and ²⁸Si⁻ ions, respectively, and an effective temperature of approximately (7.2 ± 0.1) × 10³ K of the sputtered region bombarded with pulsed 22 kV Au₃⁺ primary ions was determined. Intensity spectra showed polarity dependence on both n and m values of Si_nO_m fragments, and a slight shift to negative polarity for PECVD SiO₂ compared to thermally oxidized SiO₂ films. By dividing the intensity ratios of negative-to-positive ions for PECVD SiO₂ by those for thermally oxidized SiO₂ films to cancel statistical factors, the difference in absolute electronegativity (half the sum of ionization potential and electron affinity of fragments) between both films was obtained. An increase in electronegativity for SiO_m (m = 1, 2) and Si₂O_m (m = 1-4) fragments for PECVD SiO₂ films compared to thermally oxidized films was obtained to be 0.1-0.2 Pauling units, indicating a more covalent nature of Si-O bonds for PECVD SiO₂ films compared to the thermally oxidized SiO₂ films.     

Selective etching of InP in NaF solution

The crossing porous structure of InP has been obtained by electrochemical etching in NaF solutions. The behavior of the periodic oscillation occurs at different potential ranges for the different concentrations of solutions, and it will disappear with the concentration of the solution decreased. The scanning electron microscope (SEM) image shows that the pores have two directions on the surface and are perpendicular to each other. The two directions are assigned to [0 1 1] and [], respectively. The SEM image of the cross-section also shows that the two directions are assigned to [1 1 1]B and []B. Both are due to the selective etching of F⁻ ions. The crossing porous structure of InP is a very promising feature for the three-dimensional structure of III-V compound semiconductors for photonic band gap materials.     

Fabrication of sol-gel-derived optical waveguide on InP for hybridized photonics applications

In this paper, we report on the first successful fabrication, using spin-coating and low-temperature (200 °C) annealing, of organically modified sol-gel planar optical waveguides on InP substrates. Considering the fact that the sol-gel technique is simple and cheap, and III-V compound semiconductors are the essential substrate materials for manufacturing data communication devices, we believe that our demonstration of optical waveguiding in sol-gel-derived waveguides on III-V compound semoconductors is interesting. It opens the possibility of hybridizating traditional glass or optical-crystal-based integrated optics with III-V compound semiconductor-based optoelectronics. Received: 4 August1999 / Accepted: 6 August 1999 / Published online: 16 September 1999     

Surface chemistry and optimization of focused ion beam iodine-enhanced etching of indium phosphide

Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI₃) at room temperature. InI₃ has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III-V semiconductors.     

Er离子注入GaP,GaAs, InP的二次离子质谱(SIMS)的研究

近年来掺稀土元素的Ⅲ—Ⅴ族化合物研究在基础物理和器件应用方面都越来越引起人们的关注,[1,2]其中又由于Er3+的4I13/2—4I15/2的特征发光波长为1.54μm,恰好对应于石英光纤的低损耗区,且离子注入技术简单易行,因而倍受重视.国际上已报道了不少有关Er注入Ⅲ—Ⅴ族化合物的研究,大多选用较低的注入剂量(约1012～1014Er/cm2),而对较高剂量的注入有待于进一步研究.     

Investigation by EELS and TRIM simulation method of the interaction of Ar and N ions with the InP compound

In this study, the EELS results revealed the great sensitivity of InP compound submitted to Ar⁺ or N⁺ ions at low energy. The preliminary treatment of InP by the Ar⁺ ions was useful as part of the cleaning process of the surface. Further argon ions bombardment on cleaned InP led however to breaking of chemical bonds In–P, with desorption of phosphorus atoms and appearance of In metal distributed on InP. The damaged InP by Ar⁺ ions, constituted the diphase (In; InP) system of depth of about 30 Å, involving a superficial roughness. The In metal proportion on such a system was determined by a calculation method based on the experimental EELS spectra of pure In and InP.We submitted the heated and no heated system (In; InP) to nitrogen ions bombardment. The nitrogen reacted with the In metal to compensate the phosphorus vacancies so that InN species were formed. The heating of (In; InP) system at 450 °C, allowed the surface reconstruction with elimination of defects due to the structure and the roughness. The temperature also caused the coalescence of In metal towards the surface. Because of the physical stability of the interface of heated (In; InP) system, the nitrogen reacted with the outmost layers of In metal to form a homogeneous layer of InN of thickness estimated at 20 Å. We associated to the EELS the TRIM (Transport and Range of Ions in Matter) simulation method in order to show the mechanism of interaction Ar⁺ or N⁺ ions-InP and determine the disturbed depth as a function of the energy. The EELS alone was not able to give us with accuracy the disturbed depth of the target by these ions.     

Quasiparticle corrections to the electronic properties of anion vacancies at GaAs(110) and InP(110)

We propose a new method for calculating optical defect levels and thermodynamic charge-transition levels of point defects in semiconductors, which includes quasiparticle corrections to the Kohn-Sham eigenvalues of density-functional theory. Its applicability is demonstrated for anion vacancies at the (110) surfaces of III-V semiconductors. We find the (+/0) charge-transition level to be 0.49 eV above the surface valence-band maximum for GaAs(110) and 0.82 eV for InP(110). The results show a clear improvement over the local-density approximation and agree closely with an experimental analysis.     

Energy distributions and emission coefficients of secondary ions ejected from AIIIBV group semiconductors

The energy distributions of Ga⁺ and Ga₂ ⁺ secondary ions sputtered from the surface of single crystals of GaAs and GaP by Ar⁺ (E = 18 keV, j = 1·10^–6 A/cm²) ions were studied. Integral emission coefficients for secondary ions from four semiconductors (GaAs, GaP, InAs, and A1_0.35Ga_0.65As) bombarded by Ar⁺ ions (E = 2 keV, j₀ = 1·10^–6 A/cm²) were also measured. It is shown that the energy distribution of the Ga⁺ secondary ions are broad and qualitatively similar to distributions of secondary ions sputtered from metal oxide surfaces. Very high integral emission coefficients (up to 20–30%) for secondary ions are also observed, exceeding analogous coefficients for clean metal surfaces. These facts (the significant number of low energy secondary electrons and high secondary ion emission coefficients) are due to the lower density of free electrons in comparison with metals, which ensures a high degree of survival of sputtered ions, and the partially ionic character of the bonds in the semiconductors under study.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–92, November, 1990.     

Surface investigation of solids by the statical method of secondary ion mass spectroscopy (SIMS)

The physical and chemical properties of a solid surface are determined by its uppermost monolayers. Besides other methods like Auger electron spectroscopy (AES) and X-ray electron spectroscopy (ESCA) for example, the chemical composition of these uppermost monolayers can be investigated by the statical method of secondary ion mass spectroscopy (SIMS). In this method a relatively large target area (0.1 cm²) is bombarded with a small primary ion current density (10^?9 A cm^?2). Thus a sputtering time of several hours is achieved for an individual monolayer. A mass analysis of the emitted positive and negative secondary ions gives information about the chemical composition of the uppermost monomolecular layer of the bombarded surface. Important features of SIMS are: detection of chemical compounds; isotope sensitivity; detection of hydrogen and its compounds ; depth resolution in the range of a single monolayer ; low detection limits (< 10^?6 monolayer or < 10^?14 g) for many elements and compounds.The capacity of this method is demonstrated using as examples the initial surface oxidation of metals and semiconductors and adsorption phenomena on clean metal surfaces. In some special cases additional information on the chemical composition of the uppermost monolayer can be obtained by the electron induced ion emission from the surface.     

Properties of indium phosphite and selected compounds under irradiation with swift heavy ions

Surface and bulk properties of indium phosphate single crystals with initial and previously irradiated by 25 MeV electrons structures were irradiated with ⁸⁶Kr (253 MeV) and ¹⁹⁷Au (200 MeV) up to various fluences. The modern methods of condensed matter studies were used for research of InP property changes before and after irradiation as scanning (SEM) and high resolution transmission electronic microscopy (HTEM), Rutherford backscattering spectroscopy (RBS/C) and atomic force microscopy (AFM). The comparison of obtained results with the results of other authors is carried out. The surface structure change of InP single crystal irradiated by high-energy 86Kr ions and electrons is studied. It is shown the changes of the InP surface have complicated character and caused by inelastic sputtering processes. It is observed the twice irradiated layer swells with the cracks creation on the surface. The swelling with cracks and strong sputtering of twice irradiated by electrons and ions with high energy layers of the InP and GaAs surfaces are explained using the model based on the influence of ionizing energy loss of swift ⁸⁶Kr ions. The small crystalline objects are detected on the InP surface irradiated with ⁸⁶Kr ions which may be nano- and micro-crystals of InP. All obtained effects are discussed in frame of models based on ionizing energy loss of swift heavy ions.     

Shape cycle of Ga clusters on GaAs during coalescence growth

GaAs(1 0 0) was heated above its decomposition temperature of 585 °C bringing it into a phase separation regime where the thermodynamic favoured state is liquid Ga clusters on the surface. Varying the annealing times and temperatures provided an overview of the clustering at all stages from transitioning ripening at lower temperatures to coalescence at higher temperatures. We observed a shape cycle between round and rectangular shaped clusters during the growth. This cycle is driven by subcluster etching where pits are formed under clusters during the growth due to preferential loss of As through the liquid Ga cluster. The newly observed shape cycle is compared to a shape cycle observed previously in In on InP illustrating that shape cycles are a common feature of the decomposition of Group III-V semiconductors.     

Defects in semiconductors observed by positron annihilation

The origin of the effect of defects on positron annihilation in semiconductors has been studied. The electron-positron momentum densities in elemental semiconductors (Si and Ge), III-V compound semiconductors (GaAs, InP and GaSb), diamond and the proton irradiated Si were investigated by a full-scale use of the two-dimensional angular correlation of positron annihilation radiations (2D-ACAR). The obtained results showed, as a whole, good agreement with the electron momentum distribution of the fully occupied Jones zone with a small exception for the fact that the low density channels are running along the three principal axes. This anisotropy was strong in elemental semiconductors, while it was weakened in compound semiconductors. This anisotropy and its dependence on the material were found to be generally understood by the incorporation of crystal symmetry. The anisotropy will be discussed by group theory in conjunction to the effect of defects on positron annihilation.     

Ultraviolet photoelectron spectroscopy of nano In clusters Schottky barriers on sputtered InP

Plasmon peaks along with Auger P_LVV peak have been observed in the ultraviolet photoelectron spectra (UPSs) of InP after 5 min of sputtering with 0.5 kV Ar⁺ ions. Plasmon and Auger peaks are not observed in UPS of un-sputtered InP surface with native oxides of In and P. Filled electron energy levels are not observed near the Fermi level from 5 min sputtered InP surface due to increase of ionization potential of nano In clusters.     

Interfacial analysis of InP surface preparation using atomic hydrogen cleaning and Si interfacial control layers prior to MgO deposition

The objective of this study is to investigate how the surface characteristics of indium phosphide (InP) can be modified through the use of atomic hydrogen (H^*) cleaning and silicon interfacial control layers (Si ICL), prior to the deposition of MgO dielectric layers. X-ray photoelectron spectroscopy (XPS) analysis shows that the InP native oxide can be successfully removed using atomic hydrogen cleaning at a substrate temperature of 300 °C. However, atomic force microscopy (AFM) images display evidence for the growth of metallic In island features after H^* cleaning, and subsequent deposition of MgO thin films on the H^* cleaned surface resulted in high levels of interfacial indium oxide growth. It has also been shown that the deposition of thin (∼1 nm) Si layers on InP native oxide surfaces results in the transfer of oxygen from the InP substrate to the Si ICL and the formation of Si-InP bonds. XPS analysis indicates that MgO deposition and subsequent 500 °C annealing results in further oxidation of the Si layer. However, no evidence for the re-growth of interfacial In or P oxide species was observed, in contrast to observations on the H^* cleaned surface.     

Sulfide passivation of III-V semiconductor surfaces: role of the sulfur ionic charge and of the reaction potential of the solution

A model is proposed for describing the effect of a solution on the electronic properties of sulfided surfaces of III-V semiconductors which treats the adsorption of sulfur in terms of a Lewis oxide-base interaction. According to this model, the density of states on a sulfided surface, which pin the Fermi level, decreases as the global hardness of the electron shell of the adsorbed sulfide ions is increased. The Thomas-Fermi-Dirac method is used to calculate the global hardness of sulfide ions with different charges as a function of the dielectric constant of the medium. It is shown that the hardness of a sulfur ion is greater when its charge is lower and the dielectric constant of the solvent is lower. Zh. Tekh. Fiz. 68, 116–119 (August 1998)