High-Pressure High-Temperature Optical Floating Zone Furnace HKZ

 

The abbreviation HKZ (Hochdruck-Kristallzüchtungsanlage) stands for a unique high-pressure optical floating zone crystal growth furnace. It features a vertical 2-mirror setup with a highly homogeneous and to a great extent controllable light power distribution on the crystal rod. One of the key characteristics of the furnace is the ability to work at pressures of up to 150 bar with different gases and mixtures in the growth chamber (currently we are working on a 300 bar version). Additionally, individual gas flow rates can be adjusted and controlled freely and independently over the complete pressure range.Using powerful xenon short arc lamps, melting temperatures over 3000 °C can be achieved. While the light power tuning range of arc lamps is limited, the thermal energy in the growth chamber is step-less adjustable between 0 and 100 % thanks to a power shutter system in the light beam. HKZ versions Highly precise magnetically coupled linear and rotation feed through systems with pulling rates starting from 0.1 mm/h, advanced process monitoring technologies and a comfortable PLC user interface guarantee extensive control of the growth process. The temperature of feed rod, melt zone and crystal is measured directly via a patented in-situ temperature measurement system. An optional after-heater is applicable with all possible atmospheres and pressures—also with high-pressure oxygen atmospheres. This worldwide unique setup allows the user to rule the growth of materials, which are difficult or impossible to handle at low pressures due to the higher volatility or higher partial pressure of their elements. A very important characteristic is the highly developable and easily expandable, modular design of the HKZ furnace system, which allows add-ons and upgrades to all of current furnaces in an easy and cost-efficient way.

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Key features

HKZ special features

Practical advantages of the vertical double-ellipsoid optical scheme

Behr et al. 2010 Palme et al. "In practice, a 3, 5 or 7 kW air-cooled xenon arc lamp positioned at the focal point of the lower mirror is used as the irradiation source. The molten zone is located inside the crystal growth chamber at the focus of the upper mirror. The FZ process proceeds by vertical pulling (downwards or upwards) of the feed rod and the growing crystal. The radiation power is controlled by both the lamp electrical power and a 4-sector mechanical flux shutter positioned between the mirrors. Here, on the basis of a huge number of FZ growth experiments with various materials, the fundamental practical advantages of the presented optical scheme are summarized for the first time as a background of theoretical investigations of light propagation within the present FZ setup in order to optimize parameters for specific crystal growth purposes. Axial symmetry of this optical configuration provides extreme uniform azimuthal heating of the melting zone. It permits to control the irradiation power range absorbed by the crystal surface from 0 to 100% by both mechanical flux shutter and electrical power of the arc lamp. Due to the large size of the upper mirror (600 mm) and the narrow bundle of rays illuminating the molten zone mainly from above, there is an easy access to the crystal growth chamber, even during the growth process, and sufficient space for mounting of auxiliary functional components in the neighbourhood of the growth chamber (e.g. afterheater for growing crystal, pyrometer, camera,) without any appreciable radiation absorption. Another feature of the vertical optical configuration is the narrow region of possible incident radiation angles onto the crystal <70° due to the cut-off by the mirror (instead of almost 140–180° for horizontal optical configurations). This enables much shorter quartz tubes for the growth chamber. The very high efficiency of the radiation flux focusing was confirmed for crystallization of refractory materials. In practice only one 5 kW (electrical power) xenon lamp is required for melting refractory oxides with 2800°C melting temperature. By contrast, four 3 kW xenon lamps (12 kW in total) are necessary for achieving similar temperatures in four-mirror horizontal optical furnaces. We connect this practical result with more effective focussing of the light flux emitted by the arc lamp and a narrower light profile on the crystal surface. For example, the width of the illuminated area can be as small as 1mm for the presented optical scheme, as will be shown further, in comparison to 5 mm for the horizontal optical scheme for a point source model."
Source: Souptel, D., Löser, W., & Behr, G. (2007). Vertical optical floating zone furnace: principles of irradiation profile formation. Journal of Crystal Growth, 300(2), 538-550.
(pdf file also on caltech.edu)

 

Technical details

Atmosphere
  • Argon and oxygen (pure and in any mixture ratio)
  • Many other gases possible on request
  • Pressure: up to 150 bar (soon: 300 bar)
  • Turbulence suppression system
  • PLC controlled gas flow: 0.25 l/min to 1 l/min, individually adjustable for different gases
  • Vacuum: down to 1*10-5 mbar
  • Turbo pump close to the process chamber, wide diameter connections
  • UHV system possible on request
  • Active titanium getter gas cleaning (removes O2 traces in argon down to 10-12 ppm, applicable under high-pressure conditions)
  • Oxygen content measurement system

 

Growth chamber
  • Highly transparent material
  • Pressure-proved between 0 and 150 (300) bar
  • Long life span due to protective tube
  • Sample holder for 6,8 mm or 9,8 mm samples

 

Optical heating
  • Xenon short arc lamp, different kinds available between 3 kW and 15 kW
  • Temperature: up to 3000 °C
  • Lamp power control
  • Power shutter in the light beam, step-less adjustable between 0 and 100 %
  • Precise motor-driven lamp positioning unit, workable during the experiment
  • Upper and lower optimized elliptical mirrors, aluminum or gold coated
  • Mirror position adjustment system

 

Material rod moving
  • Precise magnetically coupled linear and rotation feed through system
  • Pulling rate: 0.1 mm/h to 200 mm/h
  • Fast service gear (approx. 0.6 mm/s )
  • Pulling length: 195 mm
  • Rotation rate: 0 to 150 rpm

 

Temperature measurement
  • Two-color pyrometer with a patented stroboscopic measurement method
  • Adjustable time interval
  • Adjustable position
  • Several temperature ranges

 

After-heater
  • Versatile and modular unit
  • Applicable with all possible atmospheres and pressures
  • Easily exchangeable heater coils
  • Highly adaptable to special needs

 

Process control and monitoring
  • High-resolution CCD camera with specialized lenses and filters
  • Monitoring application: visual control, video recordings, snapshots and length measurements during the growth process
  • Power ramp and traveling ramp functions
  • Front window for direct observation of the growth chamber
  • All system parameters are comfortably controllable and adjustable via a PLC-based software application with two 27" touch screens
  • Safety system with protection housing, door lock system, automatic shut down function

 

Required laboratory connections
  • Gas supply with the intended pressure
  • Exhaust air system
  • Energy supply: 3-phase AC, 50 Hz, 400 V, 63 A
  • Cooling water

 

Furnace dimensions
  • Height: 3020 mm , width: 1631 mm, depth: 920 mm

 

 

References

The following users of a HKZ have agreed to provide their contact data for exchange of experiences:
  • DE: Michael Schulze, Dr. Hugo Schlich, MaTecK GmbH
  • DE: Dr. A. C. Komarek, Prof. Dr. Liu Hao Tjeng, MPI CPfS Dresden
  • US: Dr. Jiaqiang Yan, Dr. Brian Sales, Oak Ridge National Laboratory
  • US: Jeniffer Zheng, Dr. John F. Mitchell, Argonne National Laboratory
  • ZH: Dr. Qisi Wang, Prof. Dr. Jun Zhao, Fudan University Shanghai
 
Publications: materials grown with the HKZ furnace system

 

Publications: methodical considerations concerning the HKZ system
 

 

HKZ 1
Fig: First HKZ generation, working facility of MaTecK GmbH, Location ScIDre GmbH Dresden