| A far-infrared p-type germanium laser prepared by neutron transmutation doping was demonstrated for the first time. Ultra pure single-crystal Ge was prepared into laser rods and neutron irradiated inside a nuclear reactor. Annealing removed lattice damage and brought majority hole concentrations to useful levels. Lasing thresholds are comparable with those of typical melt-grown laser rods, although measured compensation (determined by Neutron Activation Analysis) is higher and hole concentration (determined from resistivity measurements) is significantly lower. These are evidence of higher average gain cross section, which results from more uniform acceptor distribution achieved by neutron transmutation doping. The better doping uniformity is confirmed by current saturation behavior. Hence, neutron transmutation doping is a useful method of producing good, and potentially superior, p-Ge lasers with superior yield from the starting material. Gain improvements will be useful in miniaturizing the active medium to improve heat extraction and increasing laser duty cycle. The effects of multiple intracavity interfaces, as would be present in a proposed active-medium miniaturization and heat management scheme, were also studied. |
