Seeded growth in a soft lined crucible: Application to phosphorus doped optical germanium single crystals

Abstract

Abstract Phosphorus doped (n-type) germanium crystals have been grown by a seeded vertical gradient freeze method using a graphite crucible lined with soft graphite felt. The axial dopant distribution has been determined using the electrical resistivity and Hall effect measurements and found to deviate significantly from the normal freezing behaviour. This indicates that mixing in the melt is reduced due to the low temperature gradients in the growth system. As a result an EPD of 5 X 102 to 103 cm-2 on the (111) surface was found, which is almost by an order of magnitude lower than that of large diameter CZ pulled crystals. The homogeneity of the refractive index at 10.6 μm and the optical imaging quality (estimated from the dispersion of the Modulation Transfer Function) have been found comparable to the best CZ crystals. Further improvement of the growth method and its use for other materials is also suggested.