LPE Growth of GaInAsP/InP Heterostructures for 1.3 μm Planar Buried Mesa Lasers

LPE heterostructure growth processes devised to prepare GaInAsP/InP planar buried mesa ridge (PBMR) lasers are described. A combination of supercooling and two-step cooling regimes of LPE was used to grow InGaAsP/InP heterostructures with the active layer flanked by two waveguiding layers. The optical waveguide geometry was optimised to yield minimum threshold current density. Low-temperature (600°C) LPE process was employed to regrow the etched mesa structure. The prepared PBMR laser devices with optical resonator lengths of 250 μm exhibited room temperature threshold current values near 20 mA and T₀ values in the range 60–70K. Optical power-versus-current characteristics were linear up to 25 mW.     

Growth of p-type InP single crystals by the temperature gradient method

P-type InP single crystals doped with zinc or cadmium have been prepared from a solution using indium as a solvent in which a temperature gradient was maintained for the transport of the InP solute. The average growth rate was between 1.1 and 3.0 mm/week. The room temperature hole concentration of the crystals obtained was in a range of 10¹⁷ to 10¹⁸ cm^-3. The distribution coefficients of zinc and cadmium were 0.8 and 0.004, respectively. The temperature gradient method makes it possible to dope the crystals with volatile impurities in a controlled manner.     

Effect of In and Sb Vacancies on Temperature Dependence of InSb Lattice Parameter at High Temperatures

The temperature dependence of the thermal expansion coefficient for InSb has been determined in the range 25–515 °C by precision measurements of the lattice parameter of InSb single crystals. It is shown that beginning from 460 °C the temperature dependence of the lattice parameter for InSb single crystals grown from melts of different compositions is essentially affected by vacancies in the indium and antimony sublattices. The vacancy concentration and possible deviation of InSb from the stoichiometric composition are estimated from a relative decrease in the lattice parameter.     

Preferred Growth of Antimony Single Crystals

Single Crystals of antimony were grown by the Chalmer's method from the melt. The crystals were grown under different temperature gradients of 92 °C/cm, 75 °C/cm and 52 °C per cm. The growth velocities were varied from 1.5 cm/hr to 9 cm/hr. At low growth velocities antimony exhibits a preferred orientation in the range 1 cm/hr to 6 cm/hr. No effect of temperature gradient is observed. The results are compared with those of bismuth, cadmium and zinc which are contradictory to what has been observed.     

Deep levels and growth conditions of LPE GaAs crystals

Deep levels in LPE GaAs were studied in relation to growth conditions. The residual deep levels in LPE layers are hole traps 0.50 and 0.65 eV above the top of the valence band. Their concentrations are of the order of 10¹³ cm^-3 for growth temperatures between 650 and 840°C, and increase with increasing growth temperature. The activation energy of incorporation is about 0.7 eV, which is very close to that of an arsenic vacancy. It is also noted that their concentrations near the grown surface are independent of the growth temperature. This indicates that the hole traps undergo an annealing effect after the growth period. From the experimental results for Fe and oxygen doping, each impurity acts as a deep level only when it makes a complex defect with a gallium vacancy, otherwise they are shallow levels, The distribution coefficients at 750°C are 1 × 10^-7 and 1.1 × 10^-5 for the deep and Fe and the shallow acceptor, respectively.     

Thermal balancing via distributed inert-gas streams for high-meniscus ribbon crystal growth

Superior melt growth of ribbon crystals by thermal profile control that is continuously variable, inert, and capable of heat extraction has been achieved. In the device developed, multiple inert-gas jets are directed at various parts of the hot zone, each with individually controlled flow adjustment. In a furnace at 1200°C, the temperature at one edge of a 38-mm-wide ribbon growth zone can be varied at a rate of 6.8°C per liter per minute of argon flow. Asymmetrical temperature profiles in the zone can be flattened to within ±1°C or symmetrically tailored. Silicon ribbons having uniform widths of 38 and 50 mm and grown with a high melt meniscus have been produced by the capillary action shaping technique with inert-gas thermal balancing. Such crystals show minority carrier lifetime values of up to about 300 μs.     

LPE-growth of InP on GaAs

LPE growth of InP on GaAs is shown to be possible from indium or tin as a solvent, respectively. Only growth on (1 1 1 ) B faces yields acceptable smooth layers. From In/InP-melts layers with inclusions near the heterojunctions are obtained. No such microscopically small inclusions were observed in layers grown from Sn/InP-melts. – The grown layers were characterized by means of etching and electron beam microprobe analysis.     

Low-temperature LPE Overgrowth of InGaAs/InP Mesa Heterostructure

Preparation of planar buried mesa ridge (PBMR) epitaxial wafers suitable for integrated optoelectronic circuits is presented. For this purpose the LPE growth of InP and InGaAsP (λ_g = 1.3 μm) below 600 °C on nonplanar ridge pattern was realized. Etching of the InGaAsP/InP ridge structure with ridge of 2–2.5 μm was found to be reproducible when HBr:H₂O₂:H₂O etchant was used. The best PBMR epitaxial wafers were obtained via regrowth in multiple-bin sliding boat by two thin layers of InP using a combination of one- and two-phase growth processes between 600 and 594 °C.     

A study of the Growth-Temperature-dependent Surface Morphology in InSb Liquid Phase Epitaxy

InSb LPE layers were grown on (111) InSb substrates, their phase diagram and growth rates studied. The InSb activity coefficient α(T), determined by fitting the experimental data, had a value of 2556–11.11 · T cal · mole⁻¹. The terraces on the surface were reduced by increasing the temperature to 350 °C. Hall measurements of InSb/CdTe heterostructure failed due to the high Te segregation. The carrier concentration of these InSb epilayers, however, was determined by C-V measurements with values between 7.5 · 10¹⁴ cm⁻³ and 5 · 10¹⁵ cm⁻³.     

HigHighly strained InGaAs/GaAs quantum wells emitting beyond 1.2 µm

Highly strained In_xGa_1–xAs quantum wells (QWs) with GaAs barriers emitting around 1.2 µm are grown on GaAs substrates by metal organic vapour phase epitaxy (MOVPE) at low growth temperatures using conventional precursors. The effects of growth temperature, V/III ratio and growth rate on QW composition and luminescence properties are studied. The variation of indium incorporation with V/III ratio at a growth temperature of 510 °C is found to be opposite to the results reported for 700 °C. By an appropriate choice of the growth parameters, we could extend the room temperature photoluminescence (PL) wavelength of InGaAs/GaAs QWs up to about 1.24 µm which corresponds to an average indium content of 41% in the QW. The results of the growth study were applied to broad area laser diodes emitting at 1193 nm with low threshold current densities. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphological and structural properties of InP/Gd2O3 nanowires grown by molecular beam epitaxy on silicon substrate

InP/Gd₂O₃ heterostructures have been prepared by molecular beam epitaxy of Gd₂O₃ on InP nanowires grown on silicon substrates by molecular beam epitaxy assisted with the vapor–liquid–solid method. Transmission electron microscopy showed Gd₂O₃ nanocrystals, having diameters between 3 and 7 nm, decorating the sidewalls of InP nanowires. No epitaxial relationship was observed between Gd₂O₃ nanocrystals and InP nanowires due an amorphous interfacial layer. Depending on the Gd₂O₃ growth temperature, two morphologies have been highlighted. For Gd₂O₃ grown at 30 °C, anisotropic heterostructures made of oxide nanocrystals covering just one side of the nanowires were observed, while at 250 °C Gd₂O₃/InP core/shell nanowires were identified.     

Growth of high-purity ZnTe single crystals by the sublimation travelling heater method

A travelling heater method (THM) was developed to grow high-purity ZnTe from the vapor phase. This crystal growth method is called the “sublimation THM”. The temperature of the sublimation interface was set at 815°C and the temperature of the growth interface was varied from 785 to 800°C. The growth rate was 3 mm/day. Under these conditions, it was found that the growth process was mainly due to surface nucleation. Characteristics of the crystals were compared with those of solution-THM and vapor phase epitaxially grown crystals. The free-exciton line at 2.381 eV strongly appears and a doublet structure in neutral- acceptor bound exciton at 2.375 eV is clearly resolved with splitting energy of about 0.7 meV. We thus conclude that the THM from the vapor phase is suitable for preparing ZnTe single crystals which have excellent luminescent properties.     

The effect of cooling rate on size,quality and morphology of KTiOPO4 (KTP) crystals grown by different nucleation techniques

KTP crystals have been grown by two nucleation techniques namely spontaneous nucleation in flux medium and nucleation on Pt rod using K₆P₄O₁₃ flux.10 °C/h, 7 °C/h, 0.8 °C/h, 0.4 °C/h and 0.2 °C/h cooling rates were applied for spontaneous nucleation and crystals up to 15 × 7 × 4 mm³ in size were grown. 1 °C/h and 0.8 °C/h cooling rates were also used for nucleation on Pt rod and crystals up to 8 × 6 × 3 mm³ in size were grown. The effect of cooling rate on size, morphology and optical quality of grown crystals by both techniques were studied. For nucleation on Pt rod upper and lower rotation rates limits and an optimum rotation rate were distinguished for each cooling rate. Quality of the grown crystals by both techniques was characterized by optical transmission analysis.     

Zur Epitaxie von Galliumnitrid auf Korund im System GaCl/NH3/Ar

The vapour growth of single crystalline layers of GaN on {0001} oriented sapphire substrates in the temperature range of 500–1100°C is described for the system GaCl/NH₃/Ar. The RHEED micrographes of samples grown in the high temperature range of 1000–1050°C show KIKUCHI pattern, thus indicating a good crystalline perfection of the layers. The large free electron concentration of about 10²⁰ cm⁻³ decreases below 700°C rapidly with decreasing growth temperature. Simultaneously the crystalline perfection is remarcably lowered due to increasing misorientation of the subgrains, but no arcing of the RHEED spots due to polycrystalline behaviour is observed. The layers grown at 500°C are contaminated by chloride. Sometimes a dendritic overgrowth of the layers by the GaN sphalerite polytype takes place.     

The crystallisation of chromite-magnesiochromite spinels from a calcium magnesium aluminosilicate glass: Nucleation,crystal growth and final crystal sizes

The crystallisation of chromite-magnesiochromite spinels was studied from a calcium magnesium aluminosilicate glass (a simulated slag) containing 3 to 12 percent total iron oxides and 0.3 to 1.5 percent chromium(III) oxide, at temperatures from 1400° to 700 °C. – Spinel crystallisation occurred in glasses with 3–7 percent FeO and 0.7–1.1 percent Cr₂O₃. At temperatures 1100 °C and above, the nucleation was rapid and crystal numbers very high, at FeO contents above 3 percent and Cr₂O₃ contents above 0.7 percent; at 1056° and 1000 °C however, the crystal numbers reached some optimum values but then decreased as clinopyroxene crystals grew onto and enveloped the spinel microcrystals. In these glasses, the crystal lengths varied with growth time according to the relation, l_t = 2 k_g t^α = R_g1 t^α, where α = 0.7–1.0: this time dependence was a compromise between a relation for dendritic growth and one for facetted growth. The growth rates generally increased about five to seven times for 160 °C temperature rise: the energy of activation for the spinel crystal growth was then estimated as 180 ± 60 kJ mole⁻¹. – No spinel crystals were observed in glasses with more than 7 percent FeO content, only clinopyroxene crystals. Probably, these latter had nucleated rapidly and grown onto spinel microcrystals, while the spinel microcrystals were still of < 0.1 μm size.     

FT‐IR spectroscopic and thermal studies on pure and impurity added calcium tartrate tetrahydrate crystals

Pure and impurity (strontium) added calcium tartrate tetrahydrate single crystals were grown by the gel method. The FT‐IR spectra of these crystals were recorded in the wavenumber range 400–4000 cm^–1. The thermograms of the grown crystals were recorded in the temperature range 50–900 °C. FT‐IR spectra reveals the presence of water molecules, O‐H bond, C‐O and carbonyl C=O bonds. The thermograms show that these crystals are thermally unstable and decompose into its oxide through many stages. DTA curve of the pure crystal shows three endothermic and one exothermic peaks. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of big single crystals of Sr2YRu1‐xCuxO6 from high temperature solutions

Single crystals of Sr₂YRu_1‐xCu_xO₆ (x = 0 ‐ 0.4) have been grown from PbO‐PbF₂ based solutions in the temperature range 1150 – 1350°C. A silicon carbide heating element furnace (with a recrystallized alumina tube lining) in a vertical configuration was used to grow the crystals in platinum crucibles. Conditions for the stable growth of big crystals have been investigated. The morphology of the crystals containing Cu was found to change from octahedral to cube octahedral as the growth temperature is increased from 1150 to 1350°C. Crystals measuring up to 4.5 mm across and 2.5 mm thick have been grown from 1250°C. The incorporation of Cu into the crystals was ascertained by EDS and x‐ray diffraction analysis. A diamagnetic transition which increased in magnitude and temperature with x was observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of vertical and defect free InP nanowires on SrTiO3(001) substrate and comparison with growth on silicon

We present a study of the molecular beam epitaxy of InP nanowires (NWs) on (001) oriented SrTiO₃ (STO) substrates using vapor liquid solid mechanism and gold–indium as metal catalyst. The growth direction of InP NWs grown on STO(001) is compared with NWs grown on (001) and (111) oriented silicon substrates. Gold–indium dewetting under a flux of indium results in the majority of InP NWs growing vertically from the surface of STO(001). With the growth parameters we have used the NWs have a pure wurtzite structure and are free of stacking faults and cubic segments. The structural quality of the NWs is confirmed by micro-photoluminescence measurements showing a narrow peak linewidth of 6.5 meV.     

Growth,optical and thermal studies of nonlinear optical L‐arginine perchlorate single crystals

A potentially useful semiorganic nonlinear optical (NLO) material, L‐arginine perchlorate, has been synthesized and bulk crystals have been grown by slow cooling technique. The grown crystals were characterized by single crystal X‐ray diffraction, UV‐Vis‐NIR spectroscopy, FT‐IR, thermal analysis and SHG measurements. The grown crystals were thermally stable upto 153°C and exhibit SHG efficiency of about 0.17 with respect of Urea. The etching studies have been carried out on the grown crystal. LAPC has good optical transmission not only in the visible range, however, also in the near UV part of the spectra and hence it is a potential material for nonlinear frequency conversion. The refractive index was measured by the Brewster's angle method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and Characterization of a New Nonlinear Optical Crystal: Bis Thiourea Zinc Chloride

Bis Thiourea Zinc Chloride (BTZC) a new semiorganic nonlinear optical material has been synthesized. The solubility studies have been carried out in the temperature range 30°‐ 55°C. Single crystals of BTZC have been grown by slow evaporation of saturated aqueous solution at room temperature. The lattice parameters of the grown crystals have been determined by single crystal X‐ray diffraction technique. The UV‐Vis‐NIR transmittance spectrum has been recorded in the range 200‐2000 nm. The FT‐IR spectrum has been recorded in the range 400‐4000 cm^‐1 and the spectral bands have been compared with similar thiourea complexes.