GaAs substrate crystals with low dislocation density (Etch-Pit Density (EPD
) < 500 cm(-2)) and Si-doping (<approximate to> 10(18) cm(-3)) are required
for the epitaxial production of high-power diode-lasers. Large-size wafers
(greater than or equal to 3 in) are needed for reducing the manufacturing
costs. These requirements can be fulfilled by the Vertical Bridgman (VB) an
d Vertical Gradient Freeze (VGF) techniques. For that purpose we have devel
oped proper VB/VGF furnaces and optimized the thermal as well as the physic
o-chemical process conditions. This was strongly supported by extensive num
erical process simulation. The modeling of the VGF furnaces and processes w
as made by using a new computer code called CrysVUN++, which was recently d
eveloped in the Crystal Growth Laboratory in Erlangen.
GaAs crystals with diameters of 2 and 3 in were grown in pyrolytic Boron Ni
tride (pBN) crucibles having a small-diameter seed section and a conical pa
rt. Boric oxide was used to fully encapsulate the crystal and the melt. An
initial silicon content in the GaAs melt of C(Si-melt) = 3 x 10(19) cm(-3)
has to be used in order to achieve a carrier concentration of n = (0.8-2) x
10(18) cm(-3), which is the substrate specification of the device manufact
urer of the diode-laser. The EPD could be reduced to values between 500 cm(
-2) and 50 cm(-2) with a Si-doping level of 8 x 10(17) to 1 x 10(18) cm(-3)
. Even the 3 in wafers have rather large dislocation-free areas. The lowest
EPDs (< 100 cm(-2)) are achieved for long seed wells of the crucible.