X-ray characterization of detached-grown germanium crystals

Volz, M. P.; Schweizer, Markus; Raghothamachar, Balaji; Dudley, Michael; Szőke, János; Cobb, S. D.; Szofran, F. R.

doi:10.1016/j.jcrysgro.2006.01.025

Cited by 4 publications

(4 citation statements)

References 19 publications

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“…In agreement with results from the literature [12,13,18,25] the close contact between crucible and crystal on solidification has been found to be strongly related to the formation and polygonization of dislocations. In Fig.…”

Section: Resultssupporting

confidence: 91%

“…However, additional effort is necessary to understand and control the complex thermo-chemical equilibrium between the encapsulant and the melt (e.g., [3]). In the last 20 years VGF/VB growth without crucible contact also referred to as detached VGF/VB has attracted considerable interest as an encapsulant-free alternative to the conventional techniques [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In theoretical studies, many fundamental aspects of detached growth were investigated in great detail (e.g., Refs.…”

Section: Introductionmentioning

confidence: 99%

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VGF growth of germanium single crystals without crucible contact

Langheinrich

Pätzold

Raabe

et al. 2010

Journal of Crystal Growth

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

VGF growth of germanium single crystals without crucible contact

Langheinrich

Pätzold

Raabe

et al. 2010

Journal of Crystal Growth

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“…The dewetting phenomenon was observed for the first time in microgravity experiments [1,2] then successfully reproduced in earth experiments [3][4][5][6][7][8][9][10]. The prevailing wisdom for conducting detached growth on earth is to establish a liquid meniscus between the crystal and the crucible wall and maintain it by controlling the pressure difference between the gas space above the melt and the gap.…”

Section: Introductionmentioning

confidence: 87%

On favorable thermal fields for detached Bridgman growth

Stelian

Volz

Derby

2009

Journal of Crystal Growth

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The thermal fields of two Bridgman-like configurations, representative of real systems used in prior experiments for the detached growth of CdTe and Ge crystals, are studied. These detailed heat transfer computations are performed using the CrysMAS code and expand upon our previous analyses [14] that posited a new mechanism involving the thermal field and meniscus position to explain stable conditions for dewetted Bridgman growth. Computational results indicate that heat transfer conditions that led to successful detached growth in both of these systems are in accordance with our prior assertion, namely that the prevention of crystal reattachment to the crucible wall requires the avoidance of any undercooling of the melt meniscus during the growth run. Significantly, relatively simple process modifications that promote favorable thermal conditions for detached growth may overcome detrimental factors associated with meniscus shape and crucible wetting. Thus, these ideas may be important to advance the practice of detached growth for many materials.

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“…These results have later been corroborated by synchrotron topographs showing a reduction of dislocation densities from 10 4 cm −2 in the seed to 10 2 −10 3 cm −2 in the detached crystal, whereas for the attached crystal, the dislocation density stayed at 10 4 cm −2 or increased to 10 5 cm −2 at the periphery. 24 In addition to the direct improvement of the structural quality by detachment, there is also a secondary effect that can be positive. Because of the gap between the crystal and the wall, the heat transfer to the wall is reduced, resulting in less interface curvature and lower stress in the crystal.…”

Section: Generation Of a Pressure Differencementioning

confidence: 99%

Detached Bridgman Growth—A Standard Crystal Growth Method with a New Twist

Cröll¹,

Volz²

2009

MRS Bull.

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Bridgman or vertical gradient freeze (VGF) crystal growth processes have several advantages compared to other melt growth methods, especially the possibility to achieve a low level of thermal stress and low dislocation densities in the grown crystals. However, crystals grown in contact with a crucible usually suffer from mechanical stress during cooling, reducing the structural quality. The "detached" or "dewetted" Bridgman growth avoids this problem and has recently been investigated in more detail as a promising tool to improve crystal quality. Detached growth, where the crystal is separated from the crucible wall by a gap of 10-100 µm, was found originally in some microgravity experiments going back to 1975. Considerable improvements of crystal quality were reported for those cases; however, the reasons for the detachment were not fully understood. In the last 10-15 years, theoretical investigations as well as new experiments have shown beyond a doubt that detached growth can, in principle, be achieved in Earth's gravity with the same advantages that were demonstrated in the crystals grown under microgravity. It could be shown that the ability to achieve detachment depends on a complex interplay of the wetting of the melt with the crucible and the crystal as well as the pressure balance in the system, including the hydrostatic pressure, the gas pressure above the melt, and the pressure below the melt. It turns out that for stable detachment, only, specific combinations of meniscus shape, gap size, wetting angle, growth angle, and pressures work. The conditions that lead to detachment are thus highly specific for a given system. the crucible is stationary, and the temperature field is shifted electronically; otherwise, it is similar to the Bridgman method. Bridgman and VGF growth are used on an industrial scale for the growth of III-V and II-VI semiconductors, multicrystalline silicon for solar cells, and calcium fluoride. The advantages compared to the CZ method are a relatively simple setup, with no mechanical movement during growth in the case of VGF, suitability for systems with comparatively high vapor pressures, the possibility to grow crystals with very large dimensions, a low level of convective flow in the melt, and especially a very good control of the temperature field with small radial gradients. This allows a significant reduction of thermal stress compared to CZ-grown crystals of the same size, resulting in crystals with low dislocation densities. For instance, in the case of III-V compounds, the reduction in dislocation density can be more than an order of magnitude for VGF-grown crystals compared to liquid encapsulation CZ (LEC)-grown crystals of the same type and diameter.

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X-ray characterization of detached-grown germanium crystals

Cited by 4 publications

References 19 publications

VGF growth of germanium single crystals without crucible contact

VGF growth of germanium single crystals without crucible contact

On favorable thermal fields for detached Bridgman growth

Detached Bridgman Growth—A Standard Crystal Growth Method with a New Twist

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