Planar contact geometry for far-infrared germanium lasers

We demonstrate operation of $p-Ge$ far-infrared lasers with a planar contact geometry. The smallest laser crystal with this geometry has a maximum pulse length of 22 μs, which is 10% longer than the pulse length of comparably doped lasers with the traditional contact geometry. Calculations of the electric field distribution show that the fraction of active crystal volume for this new geometry is ∼four times larger than that of traditional geometries. Experiments and calculations reveal that in the planar design, the minimum applied voltage necessary for lasing decreases when the crystal geometry approaches a flat planar structure. This is due to a significant increase of the total electric field caused by the Hall effect.