Infrared properties of a highly compensated germanium doped with shallow donors and acceptors below the Mott transition

Highly compensated germanium crystals doped closely to the partial Mott transitions of donors and acceptors have been produced and investigated by conventional analytics to determine concentration of electrically and optically active charge centers at various temperatures. Electric measurements reveal the net active concentration in compensated, gradient-doped n -type and p -type germanium crystals, co-doped with a targeted antimony and gallium along the growth axis. Infrared absorption spectroscopy shows gradual changes in far-infrared absorption depending on the degree of compensation and the lattice temperature. This absorption can be modulated by an external light source, whose photons provide photoionization across the band gap. At lattice temperatures, corresponding to the freeze-out of free charge carriers onto Coulomb impurity centers, far-infrared absorption increases within a broad spectral band, with a maximum at approximately at the binding energy of the dopant. Such materials are suitable for a wide range of applications requiring control over of concentration, capture rates and optical absorption of free charge carriers in semiconductors.