Laser-heated floating zone crystal growth furnace LKZ

The main part of our laser-heated floating zone crystal growth furnace LKZ are five 300 W lasers with wavelength between 900 and 980 nm. The geometry and size of the laser beams which impact the sample can be changed in a wide range in order to adapt to different sample materials and rod diameters - the width and height of the preset rectangle beam can be modified easily and independently of each other. Beside the configurable laser heating system, one of the most striking features of our LKZ furnace is the possibility to perform laser-heated FZ crystal growths at high gas pressure of up to 100 bar. There are LKZ versions with 10 bar, 50 bar and 100 bar max. pressure available. The composition and pressure of the process atmosphere can be adjusted and controlled precisely with independent mass flow controllers for each gas and an easily automatable pressure regulator. This worldwide unique set-up allows the user to control the elements diffusion between melt and atmosphere to a certain grade and to rule the growth of materials, which are difficult or impossible to produce at low gas pressures due to the higher volatility of their elements or a meta-stable nature of the desired crystal phase.

The vacuum turbo pump is connected directly to the process chamber using short and wide-diameter pipes. This ensures good vacuum inside the process chamber, even below 10-5 mbar is possible. A lot of processes require an inert atmosphere with a low partial pressure of oxygen in order to perform ultra-clean growths. Our optional gas cleaning system removes oxygen traces out of argon reliably down to 10-12 ppm residual O2 concentration.

Furthermore, the temperature of the floating zone as well as of the feed and crystal rods can be measured with high-quality bi-color pyrometer or monitored by a high-resolution IR-camera. All furnaces are equipped with precise linear and rotation feed through systems for synchronous or independent rotations with up to 130 rpm and linear pullings with rates starting from 0.1 mm/h. A fast gear is implemented for rod set-up. High-pressure drives are magnetically coupled and completely capsuled without pressurized bearings.

The entire set of experimental parameters such as laser pawer, spot geometry, linear and rotational movements of the pulling drives, mass flow and gas pressure are controlled by a programmable logic controller, PLC. A comfortable software application displayed and intuitively operated via touch screens combines all relevant system information and process adjustments in one graphical user interface unit.

An important characteristic is the highly developable and easily expandable, elaborated modular design of the LKZ system, which allows add-ons and upgrades in an easy and cost-efficient way.

 

 

Laser heating

  • Number of laser diodes: 5
  • Laser power: 300 W / diode (more on request)
  • Temperature: > 2800°C (depending on material properties, e.g. transparency, reflectivity...)
  • Step-less moving/ focusing system for in situ adjustable beam (spot) size and geometry on the sample, changeable during the growth process

 

Atmosphere

  • Argon
  • Oxygen
  • pure or mixtures
  • additional gases on request
  • Flow control variable up to 1 l*min-1 (other flow rates on request)
  • Pressure up to 100 bar
  • Vacuum down to 1*10-5mbar

 

Pulling drives

  • Pulling speed 0.1..100 mm*h-1 (other speed on request)
  • Fast gear for maintenance
  • Rotary speed 0..130 min-1
  • Pulling length up to 300 mm

 

Process monitoring

  • CCD camera
  • High resolution IR camera (optional)

 

Temperature measurement (optional)

  • Two-color pyrometric measurement
  • Adjustable position
  • Several temperature ranges
  • High resolution IR camera also possible
Figure: The geometry and size of the laser beams which impact the sample can be changed in a wide range - the width and height of the preset rectangle beam can be modified easily and independently of each other in order to adapt to different sample materials and rod diameters.