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.     

The Characteristics of GaP Window Layer Grown by Indium‐added Liquid Phase Epitaxy

The effects of added Indium on the growth characteristics of GaP were systematically studied using conventional liquid phase epitaxy technique with Ga‐rich GaP source melt. The GaP growth rate uniformly increase with the source melt of increasing Indium addition against Gallium solvent. These epilayers have mirror‐like surface morphology examined by optical microscope except several grown films with large amount of Indium addition meet a terrible interface. The surface morphologies examined by AFM showed the ripples in samples of R_0.05 and R_0.4 and distinct islands with elliptical base shape in the sample of R_0.7 (R‐In ratio). The epitaxial layer with incorporation of Indium addition during growth had good performance on the carrier concentrations and resistivity. The composition of compound semiconductor become to InGaP at higher amount of In addition to Ga was examined by double‐crystal X‐ray diffraction and the distribution of Indium examined by SIMS also provided the evidences in sample of R_0.7.     

The Properties of Undoped InP and GaP Bulk Crystals Prepared by Floating Zone Melting

Undoped GaP and InP crystals which are produced by floating zone melting without a crucible were investigated. The background concentration was 10¹⁵cm⁻³ after several passages of the molten zone. The fundamental residual impurities are carbon and silicon penetrating into the crystals during the crystallization process. After purification, the electron mobility of GaP was 200 cm²/V. s, and for InP – 4000 cm²/Vs. The compensation decreased to 20%. A very effective purification was observed with respect to the carbon atoms, but for silicon this result is observed only after several passages of the molten zone. GaP and InP are basic materials for optoelectronic devices and it is important to investigate the possibility for production of pure bulk crystals. A proper method for this aim is the floating zone melting, where the crucible effect is removed and the influence of residual impurities is observed. In this work the influence of the number of floating zone passages on the electrical and luminescence properties of InP and GAP bulk crystals has been investigated.     

X-ray diffraction studies of interdiffusion in InP?GaP powder blends

Interdiffusion in the InP GaP solid solution system is investigated by means of X-ray diffraction of annealed powder blends. An activation energy of Q = (3.15 ± 0.3) eV for the interdiffusion process in the temperature interval 650… 725 °C was found. Diffusion parameters obtained by means of this method for InP GaP and InAs GaAs are discussed on the basis of lattice and atomic characteristics.     

Influence of semi-insulating InP substrates on InAlAs epilayers grown by molecular beam epitaxy

Tensile-strained InAlAs layers have been grown by solid-source molecular beam epitaxy on as-grown Fe-doped semi-insulating (SI) InP substrates and undoped SI InP substrates obtained by annealing undoped conductive InP wafers (wafer-annealed InP). The effect of the two substrates on InAlAs epilayers and InAlAs/InP type II heterostructures has been studied by using a variety of characterization techniques. Our calculation data proved that the out-diffusion of Fe atoms in InP substrate may not take place due to their low diffusion coefficient. Double-crystal X-ray diffraction measurements show that the lattice mismatch between the InAlAs layers and the two substrates is different, which is originated from their different Fe concentrations. Furthermore, photoluminescence results indicate that the type II heterostructure grown on the wafer-annealed InP substrate exhibits better optical and interface properties than that grown on the as-grown Fe-doped substrate. We have also given a physically coherent explanation on the basis of these investigations.     

Gettering Properties of Praseodymium in InGaP LPE Growth

Praseodymium (Pr) is added to the InGaP growth melt during Liquid Phase Epitaxy (LEP) for the first time. The epilayers are grown by using a supercoling method, on (100) Cr-doped Semi-Insulating (SI) GaAs substrates at a growth temperature of 790°C. An examination of the electrical properties reveals that, depending on the amount of Pr in the growth melt, n-tpye InGaP epilayers with room temperature electron concentrations in the range of 3.4 × 10¹⁶ cm⁻³ to 5.3 × 10¹⁵ cm⁻³ and electron mobilities from 730 to 1310 cm²/Vs can be prepared. The photoluminescence spectral results show that by increasing the amount of Pr in the growth melt, smaller Full Width at Half Maximum (FWHM) values and better band edge (BE) recombination intensities result.     

InP/GaP晶格失配界面的电特性

本文研究了InP/GaP晶格失配界面的电特性。HRTEM图象表明在界面存在90°位错缺陷的应变缓释。ECV表明界面存在高密度载流子层。AFM图象表明本研究中获得了粗糙度为2.48nm的良好InP异质外延层。并对于InP界面给出了一个基于费米能级钉扎的模型来解释观察到的电性质。     

Large area lateral overgrowth of mismatched InGaP on GaAs(111)B substrates

Application of InGaAs/InGaP double‐heterostructure (DH) lasers increases the band offset between the cladding layer and the active layer more than the use of conventional 1.3 µm InGaAsP/InP lasers. As a first step in realizing 1.3 µm InGaP/InGaAs/InGaP DH lasers, we proposed InGaP lattice‐mismatched epitaxial lateral overgrowth (ELO) technique and successfully carried out the InGaP growth on both GaAs (100), (111)B and InP (100) substrates by liquid phase epitaxy. In this work, we grew the InGaP crystal on GaAs (111)B substrate by adjusting Ga and P composition in In solution, to obtain In_0.79Ga_0.21P (λ = 820 nm) virtual substrate for 1.3 µm InGaAs/InGaP DH lasers. To grow the InGaP all over the lateral surface of the substrate, the growth time was extended to 6 hours. The amount of InGaP lateral growth up to 2 hours was gradually increased, but the lateral growth was saturated. The InGaP lateral width was about 250 µm at the growth time of 6 hours. We report the result that optical microscope observation, CL and X‐ray rocking curve measurements and reciprocal lattice space mapping were carried out to evaluate the crystal quality of the grown InGaP layers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental Determination of f″ for Ga and In From Bijvoet Ratio

The imaginary components of the anomalous dispersion correction terms for the heavy atoms gallium and indium, evcaluated from a systematic and precise experimetal measurement of the Bijvoet ratios for the spherically ground single crystals of GaP and InP, are reported. The procedure used is based on the work of Engel and Sturm who refined the crystal structures involving light atoms using anomalous scattering and employed the measured structure factors to evaluate the f″ values of the heavy atoms. In the present work, instead of refining the crystal structure, the structure factors are obtained using a refinement program. The experimentally evaluated f″ values are in very close agreement with the reported theoretical values.     

Enlarged ferromagnetic hysteresis in InMnP:Be epilayers formed by thermal diffusion using MBE-grown Mn/InP:Be bilayers

The p-type InMnP:Be epilayers, which were prepared by thermal diffusion of Mn through in-situ deposition of Mn layer using molecular beam epitaxy (MBE) onto MBE-grown InP:Be epilayers and subsequent in-situ annealing at 300–350 °C, were investigated. InMnP:Be epilayers prepared by the above sequence clearly showed the Mn-related emission band at 1.1–1.2 eV, which indicates the effective incorporation of Mn²⁺ ions into the host layer InP:Be. The samples demonstrated very large ferromagnetic hysteresis loops with enhanced coercivity, and the ferromagnetic-to-paramagnetic transition of the samples was observed to occur at ∼85 K. These results suggest that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be effectively formed by the above-mentioned sequential in-situ processes.     

GaAs---InP heteroepitaxy and GaAs---InP MESFET fabrication by MOVPE

Lattice-mismatched heteroepitaxy has attracted considerable attention in recent years. A great interest of these systems is the possibility of integrating devices from different materials on a single substrate. 1.3 and 1.5 μm InGaAs(P)/InP laser diodes are essential for optical communication, whereas InP field effect transistor technology is less developed than that of GaAs MESFET. The performances of laser diodes are much more sensitive to a high density of disclocations, so it would be interesting to grow GaAs MESFET on InP for integration with 1.3 and 1.5 μm lasers. Due to the large difference of the thermal expansion coefficient and lattice parameter between GaAs and InP, it is very difficult to grow GaAs epilayers of high quality on it is very difficult to grow of GaAs epilayer high quality on InP substrates due to the large difference of the thermal expansion coefficient and lattice parameter between GaAs and InP. A new method, metalorganic source modulation epitaxy (MOSME), which improves the crystal quality of GaAs epilayers on InP substrates by MOVPE, has been adopted in our laboratory. The lowest full width at half maximum (FWHM) of the double crystal X-ray (DCX) diffraction spectra reaches as low as 120 arcsec for a 5 μm thick layer. Structural properties (misorientation, lattice parameters and crystal quality) of 1.0–5.0 μm thick GaAs layers grown on InP have been measured by DCX diffraction. On GaAs MESFETs grown on InP, we have measured g_m = 100 ms/mm. For these transitions, the current gain cut-off frequency (F_t) is around 12 GHz and the maximum frequency of oscillation (F_max) is higher than 30 GHz.     

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.     

固态源分子束外延法生长InGaP/GaAs异质结构的热力学分析

本文建立了采用分子束外延法制备InGaP/GaAs异质结构的热力学模型,其中考虑了两个重要的因素,由晶格失配引起的内在应力和InP的脱附.所得到的模型与现有实验结果匹配较好.该模型的实验结果表明在InGaP的生长过程中,生长温度,In/Ga束流比及合金组分之间的相互关系,同时也与实验数据相吻合.该模型对于其他气相沉积生长方式也具有一定的适用性.     

Raman and photoluminescence analyses of the crystalline InAlAs layer grown on InP substrate

Photoluminescence and Raman measurements are used to characterize the In_xAl_1-xAs (0.48 < × <0.573)epilayers grown on InP substrate by molecular beam epitaxy. It is found that as In composition, x, deviates too much from 0.52, misfit dislocations may be introduced. These dislocations will dramatically reduce the radiative efficiency of the InAlAs epilayers. Raman spectra become broader and more asymmetry due to alloy potential fluctuations as the mismatch becomes large.     

Epitaxy and structural characterization of ZnSeTe layers grown on InP substrates

ZnSeTe epilayers were grown on InP substrates with and without ZnCdSe buffer layers. Structural X-ray and Raman characterization results indicate a large range of Se composition in the epilayers. The introduction of a buffer layer and the control of the growth conditions improve the structure by limiting compositional variations close to the stoichiometric value where lattice matching conditions are met. Effects of plastic strain relaxation are thereby minimized.     

Doping Properties of Pr2O3 Associate InP Liquid Phase Epitaxy

InP epilayers were grown on semi-insulating InP substrates by liquid phase epitaxy with Pr₂O₃-doping. Most grown layers yield mirror-like surfaces and good crystal quality. Hall measurements indicate that n-type background concentration of those grown InP layers will decrease from a value of 2.8 × 10¹⁷ to 3.0 × 10¹⁶ cm⁻³. Their correspondent 77 K mobility also varied from a value of 1326 to 3775 cm²/V s. The photoluminescence (PL) spectra of Pr₂O₃-doped InP epilayers display narrower FWHM and stronger intensity ratios (for band peak to the impurity peak). These PL spectra also demonstrate that the grown layers exhibit a pure crystal quality.     

Growth of low defect density GaP layers on Si substrates within the critical thickness by optimized shutter sequence and post-growth annealing

We have developed a growth procedure for realizing a low defect density GaP layer on an Si substrate. The growth procedure consists of two parts. One is the post-growth annealing for the annihilation of stacking faults (SFs). We have investigated an annihilation mechanism with molecular beam epitaxy grown GaP layers. 1-monolayer-thick SFs typically generate from the GaP/Si interface in a non-annealed GaP layer. In a 700 °C annealed GaP layer, generation points of these SFs tend to shift toward the GaP surface. In a 730 °C annealed GaP layer, SFs density is effectively decreased. These results suggest that SFs are annihilated through the climb motion of two partial dislocations during the post-growth annealing. Another one is the optimized shutter sequence for migration enhanced epitaxy. We have revealed that it is effective for the suppression of both three-dimensional growth and melt-back etching to increase in a stepwise manner the number of supplied Ga atoms per cycle. As a result, the generation of threading dislocations and pits is remarkably suppressed. A root mean square surface roughness of 0.13 nm is obtained within the critical thickness. We have estimated etch pit density (EPD) to be ∼7×10⁵ cm⁻² with a GaPN/GaP/Si structure. To the best of our knowledge, this value is same as that of commercially available GaP substrates and is the lowest one in the EPD of GaP/Si heteroepitaxy.     

固态源MBE系统生长高质量的调制掺杂GaAs结构材料和InP/InP外延材料的兼容性研究

通过固态源的分子束外延系统生长了调制掺杂AlGaAs/GaAs结构材料和InP/InP外延材料.在生长含磷材料之后,生长条件(真空状态)变差;我们通过采取合理的工艺方法和生长工艺条件的优化,获得了电子迁移率为1.86×105cm2/Vs(77K)调制掺杂AlGaAs/GaAs结构材料和电子迁移率为2.09×105cm2/Vs(77K)δ-Si掺杂AlGaAs/GaAs结构材料.InP/InP材料的电子迁移率为4.57×104 cm2/Vs(77K),该数值是目前国际报道最高迁移率值和最低的电子浓度的InP外延材料.成功地实现了在一个固态源分子束外延设备交替生长高质量的调制掺杂AlGaAs/GaAs结构材料和含磷材料.     

InGaAsP/InGaP superlattices by conventional MBE with molten metal solution phosphorus source

A phosphorus beam source utilizing thermal decomposition of InP is employed in a molecular beam epitaxy system. Quaternary InGaAsP films with reproducible P and As contents in the group V sublattice, and high-quality InGaAsP/InGaP superlattices with 10 and more periods were grown on (0 0 1) GaAs substrates.     

Behaviour of vicinal InP surfaces grown by MOVPE: exploitation of AFM images

InP substrates and epilayers grown by MOVPE have been studied by AFM. For different misorientation angles, we observed the surface of the substrate after annealing under phosphine (PH₃) and of the epilayers under different growth conditions such as growth temperature T_g and trimethylindium (TMI) partial pressure. After annealing the terrace width corresponds to the nominal value of misorientation angle measured by X-ray diffraction. We observed different topographies and roughnesses for the grown layers corresponding to different growth modes. We propose, taking into account the roughness of the surface, a calculation of the step height and terrace width. For 2D nucleation (θ ≤ 0.2° and T_g = 500°C) and step flow mode, the roughness is low while it is increased by step bunching (θ ≥ 0.5° and T_g ≥ 580°C). Moreover we have examined the surface morphology for different misorientation angles and determined the influence of growth conditions (growth temperature, indium partial pressure) on the growth mechanism. At T_g = 580°C the increase of the TMI partial pressure in the reactor enhances the step bunching and leads to larger terraces.