Antistructure disorder and its relation to dislocations in III–V semiconductors

Intimate relationship between antistructure defects and dislocations occurs in GaAs which manifests itself as: (i) appearing of spatial correlation between grown-in dislocations and the EL2 defects (component of the latter are As_Ga antisites), (ii) similar suppression of the concentration of EL2 and dislocation density due to the doping with donor impurities, (iii) generation of As_Ga antisites during the plastic deformation of a crystal. Al these effects can be understood in terms of the dislocation-mediated generation of As_Ga antisites via absorption of As_i interstitials at dislocation jogs. Large anion (cation) precipitates appearing at dislocations are pointed out to be important for both antisite and dislocation generation under certain conditions.     

Selective area growth of III–V compound semiconductors by chemical beam epitaxy

The reactions of triethylgallium (TEG) on a silicon nitride surface have been investigated to determine the underlying causes for selective area epitaxy. Using the techniques of X-ray photo electron spectroscopy and temperature programmed desorption, TEG is found to weakly adsorb on defect sites at room temperature. Desorption is favoured over further decomposition at higher substrate temperatures. The results are compared with the interaction of TEG on GaAs(100) surface and the implications for the influence of surface arsenic on selective area growth are discussed.     

In situ surface passivation of III–V semiconductors in MOVPE by amorphous As and P layers

A new process for chemical passivation of III–V semiconductor surfaces in metalorganic vapour phase epitaxy (MOVPE) is developed. A passivation layer is deposited directly after growth in the reactor. It consists of amorphous arsenic or a double-layer package of amorphous phosphorus and arsenic, which are grown by photo-decomposition of the group-V hydrides. These layers (caps) serve to protect the surfaces against contamination in air after removing the samples from the MOVPE growth reactor. Such passivation is applicable e.g. for a two-step epitaxy or for further surface characterizations.     

Debye temperature and melting point of II‐VI and III‐V semiconductors

In this paper, simple relations are proposed for the calculation of Debye temperature θ_D and melting point T_mof II‐VI and III‐V zincblende semiconductors. Six relations are proposed to calculate the value of θ_D. Out of these six relations, two are based on plasmon energy data and the others on molecular weight, melting point, ionicity and energy gap. Three simple relations are proposed to calculate the value of T_m. They are based on plasmon energy, molecular weight and ionicity of the semiconductors. The average percentage deviation of all nine equations was calculated. In all cases, except one, it was estimated between 3.34 to 17.42 % for θ_D and between 2.37 to 10.45 % for T_m. However, in earlier correlations, it was reported between 10.59 to 33.38% for θ_D and 6.96 to 14.95% for T_m. The lower percentage deviation shows a significant improvement over the empirical relations proposed by earlier workers. The calculated values of θ_D and T_m from all equations are in good agreement with the available experimental values and the values reported by different workers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relationship between refractive index,optical electronegativities and electronic polarizability in alkali halides,III–V,II–VI group semiconductors

Refractive indices have been evaluated from DUFFY'S optical electronegativities. The validity of the proposed empirical relation has been tested in the case of II–Vi, III–V compound semiconductors and alkali halides by comparing the calculated values of n with those in the literature. The estimated refractive indices are used in Classius-Mossotti relation to evaluate electronic polarizabilities in the above compounds. The nature of the bonding in terms of Δχ and n is discussed. Good agreement is observed between the computed and literature values of electronic polarizability.     

Isothermal contact of III–V saturated solutions with different III-V substrates: Two mode of behavior

A correlation is established between the relaxation mode of non-equilibrium solid-liquid interfaces and the sign and magnitude of the lattice mismatch between a substrate and the solid which is in equilibrium with the liquid phase contacting the substrate. For a positive mismatch of a resulting film and the substrate the relaxation proceeds via substrate dissolution or spatially separated dissolution and growth; for a negative mismatch the melt droplets penetrate into the substrate. To illustrate this correlation we use examples from the literature as well as our own experimental results on isothermal contact of binary and ternary III-V melts (saturated with respect to native solids) with different III-V substrates.     

On the use of remote RF plasma source to enhance III–V MOCVD technology

A remote RF (13.56 MHz) plasma source, assembled on a metalorganic chemical vapour deposition (MOCVD) system, was used to investigate the processes of (a) cleaning and passivation of InP substrates with H atoms (H₂ plasmas), (b) deposition of InP epilayers from In(CH₃)₃ and PH_x radicals (PH₃/H₂ plasmas), and (c) deposition of InN on sapphire from In(CH₃)₃ and N atoms (N₂---H₂---Ar plasmas). From kinetic and spectroscopic ellipsometric in situ analysis, the removal of native oxide from InP surface was found to be complete, without surface damage (phosphorus depletion), at 230°C and 7 min of H atoms exposure. The growth of InP epilayers with PH₃ plasma pre-activation was successful (stoichiometric InP) even at low V/III ratio. During InN growth, the use of optical emission spectroscopy (OES) and of in situ ellipsometry (SE) was determinant for the process control.     

A review of nanowire growth promoted by alloys and non-alloying elements with emphasis on Au-assisted III–V nanowires

Seed particles of elements or compounds which may or may not form alloys are now used extensively in promoting well-controlled nanowire growth. The technology has evolved following the well-known Vapour–Liquid–Solid (VLS) model which was developed over 40 years ago. This model indicates that a liquid alloy is formed from the seed particle and the growth precursor(s), resulting in crystal growth by precipitation from a supersaturated solution. The enhanced growth rate compared to the bulk growth from the vapour is typically attributed to preferential decomposition of precursor materials at or near the particle surface. Recently, however, there has been much interest in further developing this model, which was developed for Au-assisted Si whiskers (with diameter on the micrometre scale), in order to generally describe particle-assisted growth on the nanoscale using a variety of materials and growth systems. This review discusses the current understanding of particle-assisted nanowire growth. The aim is first to give an overview of the historical development of the model, with a discussion of potential growth mechanisms. In particular, the enhancement of growth rate in one dimension due to preferential deposition at the particle–wire interface will be discussed. Then, the particular example of III–V nanowires grown by metal–organic vapour phase epitaxy using Au particles will be revised, with details of the various growth processes involved in this system. The aim of this review is not to provide a conclusive answer to the question of why nanowires grow from seed particle alloys, but to describe the progress made towards this goal of a unified theory of growth, and to clarify the current standing of the question.     

Replacement of hydrides by TBAs and TBP for the growth of various III–V materials in production scale MOVPE reactors

Besides the standard group V precursors AsH₃ and PH₃, so-called alternative precursors like TBAs and TBP (tertiary-butyl-arsine and tertiary-butyl-phosphine) are more and more important in today's MOVPE processes. A lot of publications have demonstrated that these precursors can be successfully used for the growth of different III–V materials. In this study we want to demonstrate that TBAs and TBP can be used as the group V precursor in a complete family of production scale reactors. It is shown that these precursors can be used for the growth of InP-based as well as for GaAs-based materials. The reactors that have been employed are medium scale reactors (AIX 200/4; 1 × 2 inch, 3 or 4 inch or 3 × 2 inch capability) and large scale Planetary Reactors®, in particular the AIX 2400 system (15 × 2 inch or 5 × 4 inch). Materials that have been grown are (Al)GaInP on GaAs and GaInAsP on InP. The lower cracking energy of these precursors compared to PH₃ and AsH₃ allows one to use lower growth temperatures and lower V/III ratios, particularly in combination with the high cracking efficiencies of the used reactors. For the growth of GaInAsP on InP, the consumption of TBP and TBAs is up to 8 times lower than using PH₃ and AsH₃. GaInP on GaAs could be grown with a V/III ratio as low as 25 in a Planetary Reactor®. Good crystalline quality is demonstrated by DCXD (e.g. for GaInP: FWHM = 35 arcsec, substrate 32 arcsec). PL intensity and growth rate are not affected by using the alternative precursors. The compositional uniformity is similar to layers grown with arsine and phosphine (e.g. 1.5 nm uniformity for GaInAsP (λ = 1.5 μm) on 2 inch; approximately 1 nm uniformity for GaInP) [1,2]. The purity of the grown layers depends mainly on the quality of the TBP and TBAs. Using high purity TBP, InP revealed background carrier concentration in the mid 10¹⁴ cm⁻³ regime. Our investigation shows that TBP and TBAs can replace phosphine and arsine in state of the art MOVPE reactors. Both for single and multi-wafer production MOVPE reactors these compounds can be used successfully for the growth of the entire material spectrum in the Al---Ga---In---As---P system.     

P–T–X phase equilibrium and vapor pressure scanning of non-stoichiometry in the Cd–Zn–Te system

Technical applications of artificial crystals strongly depend on tailoring the defect structure. In compound semiconductors, native defect concentration is closely related to non-stoichiometry. Vapor pressure scanning (VPS) is a direct high precision method of in situ investigation of the composition of non-stoichiometric crystals at high temperatures. It is based on experimental measurements of the vapor pressure, from which three-dimensional P–T–X (pressure–temperature–composition) range of existence of the crystalline phase is outlined. In this communication VPS data on non-stoichiometry in the Cd–Zn–Te system are presented. Geometrical analysis of the phase equilibrium is performed, and composition of the crystal, melt and vapor is determined in the technologically most important melting region. It will be shown how to apply experimental P–T–X phase equilibrium data for preparation of the material with pre-determined composition, either stoichiometric or with a certain deviation from stoichiometry. Different technologies are analyzed: vapor-phase growth, vertical, horizontal and high-pressure Bridgman. VPS has proved to be a powerful analytical tool. For CdZnTe the accuracy of the VPS determination of non-stoichiometry was shown to be as high as 10⁻⁴ at.% for temperatures up to the melting point.     

Local structural environment and intra-4f transition of rare-earth ion in chalcogenide glass: Comparison between Dy-doped Ge–As–S and Ge–Ga–S glasses

We have employed Dy L₃-edge extended X-ray absorption fine structure measurements to investigate the local structures of Dy doped in Ge–As–S and Ge–Ga–S glasses. It turned out that Dy–S distance on average is conspicuously longer in Ge–Ga–S glass despite the number of the nearest neighboring S atoms being nearly identical with each other. The enhanced rare-earth solubility of Ge–Ga–S glass is then explained in connection with decrease in covalence of Ga–S bonds compared with Ge–S or As–S bonds, and structural correlation between GaS₄ tetrahedra and Dy. The discrepancy in the local structural environments of trivalent Dy, however, results in no significant changes in the spectral lineshape and the mean energy of its intra-4f-configurational transitions.     

Phase equilibria and prospects of crystal growth in the system LiF–GdF3–LuF3

Scheelite type LiGdF₄, LiLuF₄, and mixtures of both end members were prepared by a hydrofluorination route from the rare earth oxides and commercial LiF. The samples were purified by melting in HF/Ar mixtures, and were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and energy dispersive X‐ray spectroscopy (EDX) techniques. Both end members show unlimited miscibility in the solid phase. Mixed crystals containing at least 65 mol‐% LiLuF₄ melt under direct formation of the liquid phase. The gap between solidus and liquidus is narrow. LiGdF₄ and mixed crystals with less then 65 mol‐% LiLuF₄ decompose peritectically under formation of (Gd,Lu)F₃. Crystal growth is expected to be possible either from Lu‐rich melts with the appropriate scheelite composition or from Gd‐rich melts containing an excess of LiF. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

GaN-based lasers on SiC: influence of mirror reflectivity on L–I characteristics

The influence of the mirror reflectivity on the L–I characteristics of GaN-based lasers has been studied. A cleaved, Al-coated fiber is used as an external micro-mirror to control the reflectance of the end facets allowing for a continuous adjustment of mirror losses of a particular laser. In contrast to other methods, this eliminates all ambiguities usually arising from the comparison of different or differently coated devices. An increase in the single facet external quantum efficiency by 45% is observed for uncoated lasers and simultaneously, the threshold current is reduced by 12%. Internal losses of approximately 20–30 cm⁻¹ are derived from the differential quantum efficiency variation depending on the particular device under investigation.     

Characterization of interface states at Ni/n-Si Schottky barriers from I – V characteristics

Experiments were performed on Ni/n-Si(111) Schottky diodes fabricated by the thermal vacuum deposition of nickel on n/n⁺ Si epitaxial wafer at ˜ 10⁻⁵ torr pressure. The non-equilibrium occupation functions of the interface states were studied using the Shockley-Read-Hall (SRH) theory and considering the charge exchange between metal and interface states. Interface states density was determined from (I - V) characteristics using metal-interfacial layer-semiconductor (MIS) structure. The density was found to be in the range of 10¹² eV⁻¹ cm⁻² with a broad peak in the band gap of Si at about 0.554 eV below the conduction band edge.     

Comment on “Debye temperature and melting point of II‐VI and III‐V semiconductors” [Cryst. Res. Technol. 45, No. 9, 920–924 (2010)]

In the present work, we have readjusted some empirical parameters obtained by Kumar et al. in their work which contains some numerical errors.     

Al–O–Al and Si–O–Si sites in framework aluminosilicate glasses with Si/Al=1: quantification of framework disorder

We present for the first time, direct and clear experimental evidence of Al–O–Al and Si–O–Si linkages in charge-balanced aluminosilicate glasses with Si/Al=1, such as NaAlSiO₄ (nepheline) and LiAlSiO₄ (β-eucryptite) compositions using ¹⁷O triple quantum MAS (3QMAS) NMR and quantify the extent of disorder in framework cations (Si/Al). The degree of Al avoidance in NaAlSiO₄ glass is 0.942 at 1050 K, and in LiAlSiO₄ glass is 0.928 at 930 K (0.902 at 1050 K), which demonstrates the effect of cation field strength on the extent of disorder. In addition, we find a remarkable similarity between the ordering state of the liquid and that of the first, disequilibrium phase to crystallize.     

Raman and ESR study of sol–gel materials from ZnO–TiO2–B2O3 system

The paper studies the materials from ZnO–TiO₂–B₂O₃ ternary system, obtained by sol–gel method [1] and [2], starting from organic and inorganic precursors. The obtained samples are investigated by FTIR and Raman spectroscopy, which provide structural information, at molecular level. FTIR absorption maxima are identified and discussed according to literature data. Raman spectra are acquired by a Raman Jasco NRS-3100 spectrometer, at 532 nm wavelength and put in evidence characteristic vibration modes for all three oxide components. ESR spectra were plotted with the aid of a JES-FA 100-JEOL Japan spectrometer and titanium surrounding is investigated.     

I–V characteristics and break down studies of Sb2O3 structures

I–V characteristics of sandwiched Al–Sb₂O₃–Al structures have been studied for different thicknesses. The current-voltage curves in general exhibit three regions, ohmic, non ohmic and breakdown regions. The breakdown voltage increases whereas the dielectric strength decreases with increase in Sb₂O₃ film thickness. The electrical breakdown studies have been done for dc and ac voltages and optical photomicrographs of breakdown patterns during different stages of voltage have been taken and the results are explained.