Influence of cooling rate on the liquid-phase epitaxial growth of Zn3P2

We report the liquid-phase epitaxial growth of Zn₃P₂ on InP (1 0 0) substrates by conventional horizontal sliding boat system using 100% In solvent. Different cooling rates of 0.2–1.0 °C/min have been adopted and the influence of supercooling on the properties of the grown epilayers is analyzed. The crystal structure and quality of the grown epilayers have been studied by X-ray diffraction and high-resolution X-ray rocking measurements, which revealed a good lattice matching between the epilayers and the substrate. The supercooling-induced morphologies and composition of the epilayers were studied by scanning electron microscopy and energy dispersive X-ray analysis. The growth rate has been calculated and found that there exists a linear dependence between the growth rate and the cooling rate. Hall measurements showed that the grown layers are unintentionally doped p-type with a carrier mobility as high as 450 cm²/V s and a carrier concentration of 2.81×10¹⁸ cm⁻³ for the layers grown from 6 °C supercooled melt from the cooling rate of 0.4 °C/min.     

Agglomeration control during the selective epitaxial growth of Si raised sources and drains on ultra-thin silicon-on-insulator substrates

We have studied the impact of several Si selective epitaxial growth (SEG) process on the agglomeration of ultra-thin, patterned silicon-on-insulator (SOI) layers. Through a careful analysis of the effects of the in situ H₂ bake temperature (that followed an ex situ “HF-last” wet cleaning) and of the silicon growth temperature on the SOI film quality, we have been able to develop a low-temperature SEG process that allows the growth of Si on patterned SOI layers as thin as 3.4 nm without any agglomeration or Si moat recess at the Si window/shallow trench isolation edges. This process consists of an in situ H₂ bake at 650 °C for 2 min, followed by a ramping-up of the temperature to 750 °C, then some SEG of Si at 750 °C using a chlorinated chemistry (i.e. SiH₂Cl₂+HCl).     

A study of growth and morphological features of TiOxNy thin films prepared by MOCVD

The growth and morphological features of MOCVD TiO_xN_y films have been characterized to evaluate the effect of various process parameters on film growth. XRD analysis of the films deposited at 600°C on Si(1 1 1) and mica show a TiN(1 1 1) peak at 2θ=36.6°, but only anatase peaks are detected below 550°C. Above 650°C, both anatase and rutile peaks are detected. The presence of ammonia is not effective below 550°C as the deposited film is mostly TiO₂. Also, ammonia does not play any role in homogeneous nucleation in the gas phase, as evident by the deposition of anatase/rutile particles above 650°C. The following changes in the morphological features are observed by varying process parameters. By increasing the ratio of titanium-isopropoxide to ammonia flow, the cluster shape changes from angular to rounded; dilution of the flow results in larger elongated clusters; increase in flow rate at constant precursor to ammonia ratios, changes the cluster shape from rounded to elongated and the cluster size deceases. Deposition at higher temperatures results in finer clusters with a slower growth rate and eventually results in a very thin film with particle deposition at 650°C and above.     

High-quality InP grown by chemical beam epitaxy

InP films were grown by chemical beam epitaxy using trimethylindium (TMI) and pure phosphine (PH₃) in a flow control mode with hydrogen as the carrier gas, with the TMI flow rate fixed at 3 SCCM. Substrate temperatures were varied between 505 and 580°C and V/III ratios from 3 to 9. InP layers with high optical quality (intense and narrow excitonic transition lines) and high crystalline quality (narrow and symmetric X-ray diffraction peaks) could be grown only within a narrow parameter window around a substrate temperature of 545°C (δT_s ≤ 25°C) and a V/III ratio of 5.5 (δ(V/III) ≤ 2). Carrier densities of 8 × 10¹⁴ cm^-3 with mobilities of 70000 cm²/V.s measured at 77 K were obtained for growth conditions close to the edge of this parameter window towards low V/III ratios. The growth rate of inP was also clearly at its maximum in the given parameter window. Leaving the window, by changing either the growth temperature or the V/III ratio, significantly decreased the growth rate. This reduced growth rate was accompanied by a degradation in the crystalline quality. We also demonstrate that for higher TMI flow the parameter window shifts to higher growth temperatures. The InP could be doped effectively with Si in the range from 9 × 10¹⁵ to 3 × 10¹⁸ cm^-3.     

Properties of (Ga0.47In0.53)As epitaxial layers grown by metalorganic vapor phase epitaxy (MOVPE) using alternative arsenic precursors

In this study, the use of novel, liquid, organic arsenic precursors as substitutes for the highly toxic hydride gas arsine (AsH₃) in low pressure metalorganic vapor phase epitaxy (LP-MOVPE) of (GaIn)As lattice matched on InP has been investigated. The model precursors out of the classes of (alkyl)3-nAsH_n (n = 0,1,2) are tertiarybutyl arsine (TBAs), ditertiarybutyl arsine (DitBAsH) and diethyltertiarybutyl arsine (DEtBAs). The MOVPE growth has been investigated in the temperature range of 570–650°C using V/III ratios from 2 to 20. The obtained epitaxial layer quality as examined by means of optical and scanning electron microscopy (SEM), high resolution double crystal X-ray diffraction, temperature-dependent van der Pauw-Hall, as well as photoluminescence (PL) measurements, will be compared for the different source molecules. Under optimized conditions almost uncompensated n-type (GaIn)As layers with carrier concentrations below 1 × 10¹⁵ cm⁻³ and corresponding mobilities above 80 000 cm²/V · s have been realized. For TBAs and DitBAsH in combination with the corresponding P sources TBP and DitBuPH, respectively, we have worked out a process parameter area for the growth of layers with device quality, as proven by the realization of a pin-detector structure.     

Characteristics of ZnO–B2O3–CaO–Na2O–P2O5 glass powders prepared by spray pyrolysis

Fine-sized ZnO–B₂O₃–CaO–Na₂O–P₂O₅ glass powders with spherical shape were directly prepared by high temperature spray pyrolysis. The ZnO–B₂O₃–CaO–Na₂O–P₂O₅ powders prepared by spray pyrolysis at temperatures above 1200 °C had broad peaks at around 30° in the XRD patterns. The glass transition temperatures (T_g) of the glass powders obtained by spray pyrolysis at preparation temperatures between 900 °C and 1400 °C were near 480 °C regardless of the preparation temperatures. The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 °C had clean surface and dense inner structure at the firing temperature of 580 °C. The transmittance of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1400 °C was 90% at the firing temperature of 580 °C, in which the thickness of the dielectric layer was 13 μm. The UV cutoff edges gradually shift towards longer wavelength with increasing the preparation temperature of glass powders and the firing temperature of dielectric layers.     

Magnesium-doped InGaAs using (C2H5C5H4)2Mg: application to InP-based HBTs

Heavily magnesium-doped p-type-InGaAs layers on InP(100) substrates were successfully grown, for the first time, by low-pressure metalorganic chemical vapor deposition (MOCVD) using bis-ethylcyclopentadienyl-magnesium, (C₂H₅C₅H₄)₂Mg (EtCp₂Mg), as organometallic precursor for the Mg. It was experimentally verified that the room-temperature hole concentration of Mg into InGaAs increased with increase of the V/III ratio and decrease of the growth temperature. A maximum hole concentration of over 4 × 10¹⁹ cm⁻³ was obtained. The diffusion coefficient of Mg in InGaAs was experimentally derived to be 10⁻¹² cm²/s at 800°C, which was comparable to that of Be. Finally, InP/InGaAs heterojunction bipolar transistors (HBTs) with Mg-doped bases were fabricated successfully. Measured maximum current gain was about 320 with a 90 nm thick base and a sheet resistance of the base layer of 1.28 kΩ/sq.     

Zn-doped AlInAs grown at high temperature by metalorganic chemical vapor deposition

Zn-doped AlInAs growth at high temperature, mainly at 750°C, by metalorganic chemical vapor deposition is investigated. When introducing DEZn during AlInAs growth, it is necessary to increase the TMAl flow rate in order to make the layer lattice-matched to InP. This is due to the enhanced In incorporation rather than the large covalent radius of Zn. To clarify the electrical characteristics, the dependence of the DEZn flow rate, the V/III ratio, and the growth temperature are investigated using the van der Pauw Hall method. In our growth system, a GaInAs intermediate layer is effective in preventing n-type inversion in Zn-doped AlInAs, which occurs when it is grown directly on an InP buffer layer. In addition, a large DEZn flow rate is effective for reducing carrier compensation in Zn-doped AlInAs layers grown at 750°C. Si impurities are apparently the cause of the type-inversion and compensation in Zn-doped AlInAs.     

Formation of LiNbO3 films by hydrolysis of metal alkoxides

Homogeneous, crack-free, thin films of crystalline LiNbO₃ were synthesized above 250°C on Si(100) substrates by the dip-coating method using a double alkoxide solution. The coating solution, which was prepared by the controlled partial hydrolysis of the double alkoxide, gave stoichiometric LiNbO₃ crystalline films at temperatures as low as 250°C. The concentration of the alkoxide solution influenced both of thickness and quality of films. Crystallinity of thin film top-coated directly on the substrate affected the crystallization state of films coated on the film remarkably. Films crystallized on -Al₂O₃(0001) showed preferred orientation along the c-axis, while the preferred orientation could not be observed on Si(100) substrates.     

The crystallisation of the yttrium–sialon glass: Y15.2Si14.7Al8.7O54.1N7.4

The development of microstructure during crystallisation of a glass with composition Y_15.2Si_14.7Al_8.7O_54.1N_7.4 has been studied by analytical and high resolution transmission electron microscopy. Crystal nucleation at temperatures in the range 965–1050°C occurs by the heterogeneous nucleation of lenticular-shaped yttrium, silicon and aluminium containing crystals on silicon-rich clusters that formed during glass preparation. The lenticular crystals have a wide range of composition after heat treatment at 1050°C; the yttrium cation percentage varies around that of the expected B-phase composition Y₂SiAlO₅N but the aluminium content is lower and the silicon content generally significantly higher than that. The crystals display the hexagonal crystal structure of B-phase, although the results from EDX analysis imply that the atomic arrangement of the lattice is not the previously proposed B-phase structure. Crystal growth during prolonged heat treatment at 1050°C occurs to a significant extent by coalescence.     

Structure and thermal stability of MOCVD ZrO2 films on Si (1 0 0)

The structure and thermal stability of ZrO₂ films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO₂ nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O₂ revealed that the growth of the interfacial layer is at the expense of the ZrO₂ layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO₂ region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO₂, and SiO₂ reacted with ZrO₂ to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO₂ phase was found to be relatively easier than through the monoclinic phase.     

Effects of growth temperature and V/III ratio on surface structure and ordering in Ga0.5In0.5P

Surface photoabsorption (SPA) measurements were used to clarify the CuPt ordering mechanism in Ga_0.5In_0.5P layers grown by organometallic vapor phase epitaxy. The CuPt ordering is known to be strongly affected by the growth temperature and the input partial pressure of the phosphorus precursor, i.e. the V/III ratio. The SPA peak at 400 nm was found to be a measure of the concentration of [ 10]-oriented phosphorus dimers on the surface, which are characteristic of the (2 × 4) reconstruction. Both ordering, measured using the low temperature photoluminescence peak energy, and the SPA signal difference due to P dimers were studied versus the growth temperature and V/III ratio. The degree of order decreases markedly with increasing growth temperature above 620°C at a constant V/III ratio of 40. This corresponds directly to a decrease of the [ 10]-oriented P dimer concentration on the surface determined using SPA. Below 620°C, the degree of order decreases as the growth temperature decreases, even though the concentration of P dimers increases. The presence of an isotropic “excess P” phase observed in the SPA spectrum at 480 nm might be responsible for the decrease of CuPt ordering, although it has previously been attributed to the slow rearrangement of adatoms. The degree of order is found to decrease monotonically with decreasing V/III ratio in the range from 160 to 8 at 670°C and from 40 to 8 at 620°C. This also corresponds directly to the decrease of the P dimer concentration on the surface measured using SPA. At 620°C and a V/III ratio of 160, the degree of order decreased despite an increase of the P dimer concentration. This may also be due to the formation of the isotropic “excess P” phase on the surface. The direct correlation of the [ 10]-oriented P dimer concentration and the degree of order with changes in temperature ( ≥ 620°C) and V/III ratio (≤ 160 at 670°C and ≤ 40 at 620°C) suggests that, in this range of growth parameters, the (2 × 4) surface reconstruction is necessary to form the CuPt structure, in agreement with published theoretical studies.     

Demonstration of the N2 carrier process for LP-MOVPE of III/V''s

The suitability of an N₂ carrier in LP-MOVPE of GaInAs/InP device structures and for the growth of (Al)GaInP is investigated for the first time. Al-free GaInAs/InP HEMTs and MSM photodetectors exhibit cutoff frequencies of f_t = 135 GHz and f_max = 200 GHz and a bandwidth of 16 GHz and responsivity of 0.27 A/W, respectively. AlGaInP and GaInP layers deposited using the optimized growth conditions showed excellent structural, optical and homogeneity properties. For example X-ray diffractograms with FWHMs as low as 15–16 arcsec for 1 μm thick layers and 300 K photoluminescence mappings over full 2 inch wafers with standard deviations of ±0.23 and ±0.26 nm were obtained for both materials.     

Investigation of Ni/Au-contacts on p-GaN annealed in different atmospheres

We investigated the effect of different annealing atmospheres on contact behaviour of Ni/Au contacts on moderately doped p-GaN layers. We used the annealing gases N₂, O₂, Ar, and forming gas (N₂/H₂) at varying annealing temperatures from 350°C to 650°C in steps of 50°C. The p-GaN samples were either metalorganic chemical vapor deposition or molecular beam epitaxy grown. Contact characterization was done after each annealing step by using the circular transmission line model. Specific contact resistances were determined to be in the low 10⁻⁴ Ω cm² range for oxidized contacts. Accompanying chemical analysis using depth resolved Auger electron spectroscopy revealed that NiO was formed and Au diffused towards the interface, whereas annealing in forming gas prevented oxidation and did not lead to Ohmic behaviour.     

Correlation between interfacial structure and c-axis-orientation of LiNbO3 films grown on Si and SiO2 by electron cyclotron resonance plasma sputtering

Thin films of crystalline lithium niobate (LN) grown on Si(1 0 0) and SiO₂ substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600 °C on the Si(1 0 0) surface produced columnar domains of LiNbO₃ with well-oriented c-axes, i.e., normal to the surface. When the SiO₂ substrate was similarly exposed to plasma at temperatures above 500 °C, however, increased diffusion of Li and Nb atoms into the SiO₂ film was seen and this led to an LN–SiO₂ alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material.     

Stability and formation of pyrochlore phase in doped Sr0.8Bi2.3Ta2O9 thin films

Ferroelectric thin films of bismuth-containing layered perovskite Sr_0.8Bi_2.3Ta_2−xM_xO₉ (SBTM), where M is V, Ti, W, and Zr, have been prepared on Pt/Ti/SiO₂/Si substrates using the metal-organic decomposition method. The effect of the incorporated B-site cations on pyrochlore phase formation and microstructure evolution of SBTM films was investigated. The pyrochlore phase formation has been identified due to out-diffusion of titanium from underneath platinum layer to participate in the reaction with the films. Furthermore, the formation of pyrochlore phase in the SBTM films has been observed strongly dependent on the characteristics of incorporated M cation. The substitution of both W and V for Ta leads to the formation of pyrochlore phase at lower annealing temperature (750–800 °C). On the other hand, the addition of Zr can retard the formation of pyrochlore phase from 850 to 900 °C. A model based on the binding energy of octahedral structure is used to elucidate the formation and stability of the pyrochlore phase present in the SBT film.     

HREM investigations of intermediate ZnO and ZnO/Y–ZrO2 layers in Y–ZrO2 bicrystals and ZnO films grown on Y–ZrO2 bicrystal substrates

The structure of yttrium-stabilized ZrO₂ (YSZ) bicrystals with ZnO and ZnO/YSZ/ZnO/YSZ/ZnO intermediate layers, as well as ZnO films grown on YSZ bicrystal (1 1 0)/90° substrates, has been investigated by means of high-resolution electron microscopy (HREM) and microanalysis. All bicrystals were produced by the solid-phase intergrowth (SPI) method. The internal ZnO film in the bicrystal formed at the SPI temperature of 1400°C consisted of domains with two symmetrical orientations: , and , . A bicrystal with a ZnO/YSZ/ZnO/YSZ/ZnO internal film was formed at the temperature of 1200°C. There was no mixing of ZnO and YSZ films and no traces of any solid-phase reactions were observed. Grains in all internal ZnO films and ZnO films grown on the bicrystal substrates had numerous stacking faults. It was found that SPI does not influence the density and structure of these defects. Orientational relationships between YSZ and ZnO in all samples were determined. The ZnO films grown on (1 1 0)/90° bicrystal substrates inherited the grain boundary (GB) from the substrate. Its structure and geometry is determined by four variants of ZnO grain growth.     

Electronic traps in mixed Si1−xGexO2 films

Thermally stimulated luminescence (TSL) and infrared (IR) spectroscopy were measured in plasma grown Si_1−xGe_xO₂ (x=0, 0.08, 0.15, 0.25, 0.5) with different thicknesses (12–40 nm). A comparison with the TSL properties of thermally grown SiO₂ and GeO₂ was also performed. A main IR absorption structure was detected, due to the superposition of the peaks related to the asymmetric O stretching modes of (i) Si–O–Si (at ≈1060 cm⁻¹) and (ii) Si–O–Ge (at 1001 cm⁻¹). Another peak at ≈860 cm⁻¹ was observed only for Ge concentrations, x>0.15, corresponding to the asymmetric O stretching mode in Ge–O–Ge bonds. A TSL peak was observed at 70°C, and a smaller structure at around 200°C. The 70°C peak was more intense in all Ge rich layers than in plasma grown SiO₂. Based on the thickness dependence of the signal intensity we propose that at Ge concentrations 0.25x0.5 TSL active defects are localised at interfacial regions (oxide/semiconductor, Ge poor/Ge rich internal interface, oxide external surface/atmosphere). Based on similarities between TSL glow curves in plasma grown Si_1−xGe_xO₂, thermally grown GeO₂ and SiO₂ we propose that oxygen vacancy related defects are trapping states in Si_1−xGe_xO₂ and GeO₂.     

Improved tensile ductility of amorphous Fe78Si9B13 alloy using electrodeposited nano-Ni layers

In order to improve the tensile ductility of amorphous Fe₇₈Si₉B₁₃ alloy, nano-Ni layers were electrodeposited on the amorphous alloy ribbon and amorphous Fe₇₈Si₉B₁₃/nano-Ni laminated composite was prepared. The tensile ductility of laminated composite and monolithic amorphous alloy at both room and high temperatures was examined. The elongation of the amorphous Fe₇₈Si₉B₁₃ alloy and that in the laminated composite increases from 1.4% to 8.5% and from 36.3% to 115.5% at room temperature and 450 °C, respectively. The improved tensile ductility using electrodeposited nano-Ni layers is attributed to a good bonding between the amorphous Fe₇₈Si₉B₁₃ layer and nano-Ni layers. The amorphous layer can deform in conformity with Ni layers and be significantly stretched without fracture.     

Transmission electron microscopy observation of GaAs/Al0.3Ga0.7As T-shaped quantum well structure fabricated by glancing angle molecular beam epitaxy on GaAs(100) reverse-mesa etched substrates

GaAs/Al_0.3Ga_0.7As multi-layer structures were grown on GaAs (100) reverse-mesa etched substrates by glancing angle molecular beam epitaxy (GA-MBE). A(111)B facet was formed as a side-facet. Surface migration of Ga and Al atoms from the (100) flat region to the (111)B side-facet region has been investigated to fabricate T-shaped GaAs/AlGaAs quantum wells (QWs) under the condition that Ga and Al atoms impinge only an the (100) flat region and do not impinge on the (111)B side-facet. Observation of T-shaped GaAs/AlGaAs quantum wires (QWRs) by cross-sectional transmission electron microscopy (TEM) revealed that there is no migration of Al atoms from the (100) to the (111)B facet region at a substrate temperature (T_s) as high as 630°C, under a V/III ratio of 28 (in pressure ratio). On the other hand, very thin GaAs epitaxial layers grown on the (111)B side-facet region owing to the Ga migration were observed for substrate temperatures of 600 and 630°C. It was found that the mass flow of Ga atoms from the (100) region to the (111)B side-facet region increases, with the thermal activation energy of 2.0 eV, as the substrate temperature increases from 570 to 630°C. The GA-MBE growth on a reverse-mesa etched GaAs substrate at a low temperature 570°C or lower is desirable to fabricate a nm-scale GaAs/AlGaAs QWR structure with nm-scale precision.