Vapour Pressure Controlled Czochralski Research Articles

Boron‐ and stoichiometry‐related defect engineering during B2O3‐free GaAs crystal growth

AbstractGaAs crystals have been grown without B2O3 encapsulation by the vapour‐pressure controlled Czochralski (VCz) method to reduce undesired boron incorporation and to enable in situ control of the Ga/As ratio in the melt. With increasing Ga content of the melt the omnipresent As precipitate concentration decreases in as‐grown GaAs crystals. Semiinsulating (SI) GaAs crystals could been obtained even from melts with a composition of 46 at.% As. Comparative cathodoluminescence (CL) measurements on those crystals and on boron‐contaminated GaAs show that the luminescence bands at 1.316 eV and at 1.441 eV are related to BAs. Reduced concentrations of boron and EL2 result in significant lower near‐band edge absorption, mainly caused by the photoionization cross section of As antisites in SI GaAs. These VCz GaAs crystals possess improved optical properties. Semi‐conducting (SC) GaAs:Si crystals were grown from near‐stoichiometric melts. Positron annihilation lifetime spectroscopy measurements show that the low boron concentration in our SC VCz GaAs results always in 3 times higher Ga vacancy concentrations compared to standard SC GaAs. CL bands due to optical transitions at 0.95 eV and 1.15 eV are related to auto‐compensating (VGaSiGa)2‐ and (SiGaVGaSiGa)– complexes, respectively, and depend on the doping level. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of twin formation in sphalerite-type compound semiconductors: A model study on bulk InP using statistical methods

The type of twinning in sphalerite-type III–V compound semiconductors is well known. However, the detailed formation mechanism, although intensively studied in the last two decades, is not entirely understood. It is still widely accepted that twin formation is a rather fortuitous issue. In addition to many empirical observations and phenomenological explanations, there was a first theoretical approach by Hurle [Speculation Concerning the Causes of Twinning during Czochralski growth of Crystals having Diamond Cubic or Zinc-blende Structure, 1991], later refined. The theory predicts a correlation between crystal slope angle α and twin generation frequency, where α is defined as the angle between the tangent to the crystal surface and the growth axis. Angles of 70 . 53 ∘ and 74 . 21 ∘ should promote twinning, while that of 35 . 26 ∘ should reduce twin frequency. However, a critical review of experimental results on InP, grown by LEC (liquid encapsulated Czochralski) and VCz (vapor pressure controlled Czochralski) techniques, does not yield such a clear correlation. To shed some more light on the possible factors already discussed in literature, a systematic study based on statistical methods is performed. It can be shown that, at least for the Czochralski technique, twin formation is closely connected to the crystal growth rate and its fluctuations, i.e. instabilities of the growth system. This confirms some of the literature suggestions.

Crystal growth by a modified vapor pressure-controlled Czochralski (VCz) technique

A modified vapor pressure-controlled Czochralski (VCz) method is reported which employs a diving bell around the growing crystal. Semi-insulating (SI) GaAs crystals with a diameter of 160 mm and an overall length up to 220 mm were grown from melts of up to 23 kg, and compared with similar-sized crystals grown using a standard liquid-encapsulation Czochralski (LEC) process. Optimization of the VCz process was assisted by global numerical simulations. A slightly convex growth interface has been found to be the most suitable one for achieving a relatively low EPD of ∼10 4 cm −2 , with an associated reduction in the probability of dislocation bunching. The carbon concentration of the crystals was controlled down to values of 10 14 cm −3 . The electrical properties, including the EL2° content are discussed.

Defect distribution in boron-reduced GaAs crystals grown by vapour-pressure-controlled Czochralski technique

GaAs crystals have been grown without B 2 O 3 encapsulation by the vapour-pressure-controlled Czochralski (VCz) method to reduce undesired boron incorporation and to enable in situ control of the Ga/As ratio in the melt. Semi-insulating boron-reduced 2 and 3 in diameter twin-free GaAs crystals were grown from Ga-rich melts with compositions down to 46 at% arsenic. Cathodoluminescence (CL) measurements on crystals grown from Ga-rich melts show that the luminescence bands at 1.316 and at 1.441 eV are related to the B As . Semiconducting GaAs crystals were grown from stoichiometric melts. The donor was incorporated by silicon doping or using fused silica crucibles. Performing positron annihilation lifetime spectroscopy shows that the low boron concentrations in our semi-conducting VCz GaAs result always in higher Ga vacancy concentrations compared to standard GaAs. CL bands due to optical transitions at 0.95 and 1.15 eV are related to auto-compensating (V Ga Si Ga ) 2− and (Si Ga V Ga Si Ga ) − complexes, respectively, and depend on the doping level.

Vacancy-type defects in boron-reduced VCz GaAs crystals

GaAs crystals have been grown by the vapour pressure controlled Czochralski (VCz) method without boric oxide encapsulant. The melt compositions were in situ controlled and the carbon concentration adjusted. Low doped p- and n-type conducting GaAs has been studied with respect to their content of native and extrinsic defects. The influence of low boron concentrations on vacancy-type defects investigated by positron annihilation technique and cathodoluminescence are presented. The results are discussed in comparison with those obtained on conventionally grown material.

Development of a software for the numerical simulation of VCz growth under the influence of a traveling magnetic field

A software for the numerical simulation of crystal growth from the melt under the influence of a traveling magnetic field was developed by coupling a global stationary simulation of the temperature distribution and the electro-magnetic fields to a local transient simulation of the melt. Numerical results of the simulation of the vapor pressure controlled Czochralski (VCz) growth of GaAs are presented.

Growth and characterization of GaAs crystals produced by the VCz method without boric oxide encapsulation

Unintentionally doped GaAs crystals grown from Ga-rich melts without B 2O 3 encapsulation by the modified vapour pressure controlled Czochralski (VCz) method are analysed. The influence of this growth technique on dislocation density and distribution is presented. The concentration of As precipitates in dependence on the melt composition is shown. Finally, the contents of residual impurities and their influence on some characteristic electrical parameters are discussed. The attention is focused on the feasibility of in situ controlled near-stoichiometric semi-insulating (SI) GaAs crystals with minimized content of As precipitates.

Quick mapping of carrier concentration in InP substrate with large diameter by near-infrared transmittance measurement

In order to assess macroscopic and microscopic profiles of carrier concentration in n-type InP substrates, near-infrared (NIR) transmittance has been measured and quantitatively converted into the term of carrier concentration with the calibration curve determined experimentally in the range from 1×10 18 to 6.4×10 18 cm −3. The InP substrate assessed here was a 4-in S-doped substrate grown by the vapor-pressure-controlled Czochralski (VCZ) technique. It was found that the radial profile of carrier concentration was macroscopically concave. An elliptical striation pattern due to microscopic fluctuation of carrier concentration was observed, which seemed to be originating from unwanted asymmetry in the VCZ growth process. The macroscopic and microscopic profiles of carrier concentration may provide very important information about the crystal growth situations such as the shape of solid–liquid interface and the stability of crystal growth.

2D simulation of carbon transport at the growth of GaAS crystals by liquid encapsulated Czochralski techniques

We present a 2D model for the unsteady carbon transport and incorporation into the crystal during the vapor pressure-controlled Czochralski growth of semi-insulating GaAs. The model is based on a conjugated analysis of global heat transfer, turbulent melt convection, and the flow in the encapsulant within a quasi steady-state approximation. Carbon transport in the melt is coupled to the transport of carbon monoxide in B 2O 3 encapsulant, assuming CO dissolution at the melt/encapsulant interface. CO concentration in the gas near the encapsulant surface, estimated from experimental observations, is used to formulate an external boundary condition. The model is validated using measurements of carbon concentration in grown 3-in GaAs crystals. The results obtained help to reveal basic mechanisms controlling carbon incorporation into the crystal.

Growth of GaAs crystals from Ga-rich melts by the VCz method without liquid encapsulation

The growth experiments and properties of undoped GaAs crystals grown by the vapour pressure controlled Czochralski (VCz) method without boric oxide encapsulant from Ga-rich melts are presented. Morphological and structural features were investigated by sensitive etching procedures. The precipitate content was analysed by laser scattering tomography. The mean scattering intensity of As precipitates decreases with increasing Ga excess in the melt. An enhanced probability of Ga-rich inclusion incorporation has been observed. In 3-in crystals, the mean etch pit density was decreased down to 5×10 3 cm −2 with improved radial homogeneity. The etch pits did not show cell patterning. Markedly reduced contents of boron and hydrogen have been detected. No oxygen defects and related complexes independently on the carbon concentration were ascertained by local vibrational mode. For the first time, the carbon concentration in the grown crystals was reduced by carefully controlling the CO content of the growth atmosphere in a VCz arrangement without boric oxide encapsulant. Such experiments without B 2O 3 encapsulant are of fundamental character and offer numerous information about the point defect situation in as-grown crystals.

Non-stoichiometric growth of GaAs by the vapour pressure controlled Czochralski (VCz) method without B 2O 3 encapsulation

Results of the growth of semi-insulating GaAs crystals by the VCz method without B 2O 3 encapsulant are presented. Crystals have been grown from Ga-rich and near-stoichiometric melts controlled by As partial pressure in the range from 590°C to 630°C. The CO content in the gas atmosphere has been controlled. We investigated the influence of melt composition, reduced boron incorporation and adjusted carbon concentration. Native and impurity defect concentrations are compared with those of conventional VCz samples.

Synchrotron X-ray topography of undoped VCz GaAs crystals

For the first time vapour pressure controlled Czochralski (VCz) monocrystals of semi-insulating (SI) GaAs, grown at IKZ Berlin, have been investigated by synchrotron X-ray topography. The X-ray topographs of a typical VCz sample, taken from the cylindrical part, show dislocation images resembling those of SI vertical gradient freeze-grown GaAs crystals. From the disappearance of the dislocation image in selected topographs it is concluded that the Burgers vector for most dislocations is parallel to 〈1 1 0〉. The main part proves to be of 60° type. The cellular structure, typical for liquid encapsulated Czochralski material, is not seen in the VCz samples. Large volumes up to 0.5×0.5×0.5 mm 3 are dislocation-free. The results are compared with etch pit density (EPD) measurements from the same crystals. The average EPD is (1–2)×10 4 cm −2. The minimum value along 〈1 1 0〉 is 2×10 3 cm −2.

A numerical investigation of the effects of iso- and counter-rotation on the shape of the VCz growth interface

The flow in the GaAs and boron oxide melt in an equipment used for the vapour pressure controlled Czochralski (VCz) growth has been calculated. Two-dimensional-axisymmetric calculations have been performed by using the commercial general purpose program FIDAP TM. The influence of iso- and counter-rotation on the shape of the interface has been studied.

Quantitative approaches in laser scattering tomography

Laser scattering tomography (LST) is extended to quantitative measurements and to macroscopic fields. A technique is described to image patterns of submicroscopic scatterers decorating defects in depths up to a few mm without focus degradation. It is especially useful to reveal the arrangement of precipitates of low concentration and assures the proportionality between the measured intensity of the scatterer and its scattering cross-section. The relative volumes of the submicroscopic precipitates are determined from the measured intensities. The extended LST technique is demonstrated for GaAs crystals grown by the vapour pressure controlled Czochralski (VCz) technique. Statistically relevant histograms of the volumes of submicroscopic As precipitates are presented. By Fourier analysis planes preferably populated by decorated dislocations can be evaluated for their orientation. Dependencies along macroscopic dimensions of the samples can be measured, e.g. along a wafer radius.

Laser scattering experiments in VCz GaAs

The method of laser scattering tomography (LST) was adapted to investigate scatterers in semi-insulating GaAs grown by the vapour pressure controlled Czochralski (VCz) technique. The LST method was extended to evaluate quantitatively the scattering for macroscopic fields. The LST images of as-grown VCz GaAs crystals showed a reduced number of scattering particles in comparison with conventional LEC crystals. The dependency of the total scattered intensities along a wafer radius and intensity histograms are discussed.

Global temperature field simulation of the vapour pressure controlled Czochralski (VCZ) growth of 3″–4″ gallium arsenide crystals

The vapour pressure controlled Czochralski (VCZ) method belongs to the new methods to provide low-gradient temperature fields during the growth of III–V crystals. For the first time a global two-dimensional model of the VCZ growth of 3″ and 4″ GaAs crystals is presented. The finite volume code CrysVUN++ was used to simulate heat transfer taking into account conduction and radiation in the whole equipment. Thermoelastic stresses are analysed in terms of the von-Mises stress. There is a good agreement between measured and calculated values, e.g., of the convexity of the crystal-melt interface.

Low dislocation density Si-doped GaAs single crystal grown by the vapor-pressure-controlled Czochralski method

Si-doped GaAs substrates have been widely used for optical devices. Recently, as the device fabrication process has changed, larger diameter substrates can be used. Almost dislocation-free Si-doped GaAs crystals of 75 mm diameter, which are suitable for the fabrication of optical devices, have been successfully grown using our vapor-pressure-controlled Czochralski (VCZ) method. The generation of slip dislocations could be suppressed and the growth of the dislocation-free crystal was achieved by decreasing the thickness of B2O3. The VCZ crystals contained a large amount of unintentionally doped boron (B) of about 1018 cm−3. By comparing the electrical data of the VCZ crystals with those of the gradient freeze (GF) crystal free from B, it is found that B acceptors decrease the intrinsic compensation ratio ([SiAs][SiGa]).

Vapour pressure controlled Czochralski (VCZ) growth — a method to produce electronic materials with low dislocation density

Crystal Research and TechnologyVolume 32, Issue 1 p. 35-50 Review Vapour pressure controlled Czochralski (VCZ) growth — a method to produce electronic materials with low dislocation density† Prof. Dr. P. Rudolph, Prof. Dr. P. Rudolph Institut für Kristallzüchtuug, Rudower Chaussee 6, D-12489 Berlin, GermanySearch for more papers by this authorDr. M. Neubert, Dr. M. Neubert Institut für Kristallzüchtuug, Rudower Chaussee 6, D-12489 Berlin, GermanySearch for more papers by this authorS. Arulkumaran, S. Arulkumaran Crystal Growth Centre Anna University India Madras — 600 025Search for more papers by this authorM. Seifert, M. Seifert Institut für Kristallzüchtuug, Rudower Chaussee 6, D-12489 Berlin, GermanySearch for more papers by this author Prof. Dr. P. Rudolph, Prof. Dr. P. Rudolph Institut für Kristallzüchtuug, Rudower Chaussee 6, D-12489 Berlin, GermanySearch for more papers by this authorDr. M. Neubert, Dr. M. Neubert Institut für Kristallzüchtuug, Rudower Chaussee 6, D-12489 Berlin, GermanySearch for more papers by this authorS. Arulkumaran, S. Arulkumaran Crystal Growth Centre Anna University India Madras — 600 025Search for more papers by this authorM. Seifert, M. Seifert Institut für Kristallzüchtuug, Rudower Chaussee 6, D-12489 Berlin, GermanySearch for more papers by this author First published: 19 February 2006 https://doi.org/10.1002/crat.2170320104Citations: 21 † Dedicated to Professor Dr. Hennann Neels on the occasion of the 30th anniversary of his Editorship of Crystal Research and Technology AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume32, Issue11997Pages 35-50 RelatedInformation

Fine structures of residual strain distribution in Fe-Doped lnP-100) wafers grown by the LEC and VCZ methods

By using a high-spatial-resolution scanning infrared polariscope, in-plane components of residual strain have been characterized quantitatively in 2′Φ wafers of Fe-doped InP( 100) single crystals grown by the liquid-encapsulated Czochralski (LEC) and the vapor pressure controlled Czochralski (VCZ) methods. The twodimensional distribution maps of LEC-grown wafers reveal characteristic fine structures such as slip-like patterns originated from crystallographic glides during the crystal growth process, highly strained spots and filaments due to inclusions or voids inside the wafer, or due to scratches on the surface. The sliplike patterns are seldom observed in the VCZ-grown wafers. The residual strain value averaged over the whole region of wafer is also examined, together with etch pit density and resistivity, as a function of the solidified fraction. It is found that the residual strain in the Fe-doped InP crystals grown by the LEC and VCZ methods mainly depends on the thermal stress during the growth process rather than on the impurity-hardening effect of Fe.Key words: InP, infrared polariscope, liquid-encapsulated Czochralski (LEC) method, residual strain, vapor pressure controlled Czochralski (VCZ) method

Growth and characterization of III–V materials grown by vapor-pressure-controlled Czochralski method: comparison with standard liquid-encapsulated Czochralski materials

By using the vapor-pressure-controlled Czochralski (VCZ) method, we successfully grew both InP and GaAs single crystals which had very low dislocation densities one order of magnitude less than those of liquid-encapsulated Czochralski (LEC) single crystals. The residual strain of the VCZ GaAs substrate was one-quarter of that of the LEC substrate, and the generation of slip dislocations on the substrates during molecular beam epitaxy growth was significantly improved on the VCZ substrates. In the sulfur-doped VCZ InP crystal with no slip dislocation, the VPE InGaAs layer grown on the substrate exhibited few propagating dislocations and a very low leak current.