Gerald W. Iseler

Vertical gradient freezing of doped gallium–antimonide semiconductor crystals using submerged heater growth and electromagnetic stirring

Abstract An investigation of the melt growth of uniformly doped gallium–antimonide (GaSb) semiconductor crystals as well as other III–V alloy crystals with uniform composition are underway at the US Air Force Research Laboratory at Hanscom Air Force Base by the vertical gradient freeze (VGF) method utilizing a submerged heater. Stirring can be induced in the GaSb melt just above the crystal growth interface by applying a small radial electric current in the liquid together with an axial magnetic field. The transport of any dopant and/or alloy component by the stirring can promote better melt homogeneity and allow for more rapid growth rates before the onset of constitutional supercooling. This paper presents a numerical model for the unsteady transport of a dopant during the VGF process by submerged heater growth with a steady axial magnetic field and a steady radial electric current. As the strength of the electromagnetic (EM) stirring increases, the convective dopant transport increases, the dopant transport in the melt reaches a steady state at an earlier time during growth, and the top of the crystal which has solidified after a steady state has been achieved exhibits axial dopant homogeneity. For crystal growth with stronger EM stirring, the crystal exhibits less radial segregation and the axially homogeneous section of the crystal is longer. Dopant distributions in the crystal and in the melt at several different stages during growth are presented.

Combining Static and Rotating Magnetic Fields During Modified Vertical Bridgman Crystal Growth

Static magnetic fields have been widely used to control the heat and mass transfer during crystal growth, whereas rotating magnetic fields are attracting a growing attention for crystal-growth technologies from the melt A combination of static and rotating magnetic fields can be used to control the transport phenomena during semiconductor crystal growth. This paper treats the flow of molten gallium-antimonide and the dopant transport during the vertical Bridgman process using submerged heater growth in this combination of externally applied fields. This paper investigates the effects of these fields on the transport in the melt and on the dopant distributions in the crystal.

Parametric Study of Modified Vertical Bridgman Growth in a Rotating Magnetic Field

Using the vertical Bridgman process, a single semiconductor crystal is grown by the solidification of an initially molten semiconductor (melt) contained in a crucible. In addition to the main Bridgman heater, a submerged heater is added that separates the melt into two zones, i.e., an upper melt and a lower melt that is continuously replenished with fluid from the upper melt to offset the rejection of species along the crystal-melt interface. As crystal growth progresses, the crucible is slowly lowered to maintain a constant lower melt depth. An externally applied rotating magnetic field produced by a synchronous motor stator is used to control the transport of the electrically conducting molten semiconductor. This paper treats the flow of a molten semiconductor and the dopant transport during the vertical Bridgman process with a submerged heater and with a transverse rotating magnetic field. This paper also investigates the effects of the crystal radius, the melt depth, the strength of the magnetic field, and the number of poles in the inductor on the dopant distributions in the crystal.

Improved phosphorus injection synthesis for bulk InP

High purity, stoichiometric InP is being produced in crucible-shaped, 3-kg charges by the phosphorus injection method in a high-pressure magnetic liquid encapsulated Czochralski (MLEC) crystal growth system. Dedicated heaters in the phosphorus injector assembly are used to heat and controllably inject the phosphorus vapor into the liquid encapsulated indium melt. Glow discharge mass spectroscopy and van der Pauw measurements of the polycrystalline charges and the Czochralski wafers confirmed the low background levels of impurities.