Amplification of terahertz radiation in delta-doped germanium thin films

A new geometry for the intersubband THz laser on delta-doped multi-layer Ge thin films with in-plane transport of carriers in crossed electric and magnetic fields is proposed. A remarkable increase of the gain compared to existing bulk p-Ge lasers is based on spatial separation of light and heavy hole streams, which helps to eliminate scattering of light holes on ionized impurities and the majority of heavy holes. Inversion population and the gain have been studied using Monte-Carlo simulation. The terahertz transparency of a CVD-grown delta-doped Ge test structure has been experimentally studied by intracavity laser absorption spectroscopy using a bulk p-Ge laser. A practical goal of this study is development of a widely tunable (2-4 THz) laser based on intersubband hole transitions in thin germanium films with the gain sufficient to operate at liquid nitrogen temperatures.