GaAs substrates for high-power diode lasers

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.