Growth of Mercury-Based Films and Quantum Well Structures by Molecular Beam Epitaxy.

Molecular beam epitaxial (MBE) growth of selected Hg-based semiconductors and superlattices was studied. An MBE system specifically designed for growing Hg-based thin films and multilayer structures was constructed. It consists of a preparation and analysis chamber, a main MBE growth chamber, and a load lock for introducing or retrieving samples from either chamber. The high vapor pressure and low sticking coefficient of Hg necessitated design considerations for Hg usage. The design of the system considered such things as the ultra high vacuum pumping system, the Hg source, Hg containment, and Hg removal. The MBE system has been used to grow CdTe, HgCdTe, HgTe, and HgMnTe thin films. The optical, electrical, and structural properties of the thin films were studied. HgTe is a negative band gap semiconductor. This property gives rise to interesting physical properties in alloys of Hg _{rm 1-x}Cd _{rm x}Te and Hg _{rm 1-x}Mn_ {rm x}Te including variation of the band gap over most of the infrared spectral region by varying the mole fraction x. The addition of Mn to the lattice leads to many interesting magnetic effects. The MBE system was employed to grow HgTe-CdTe and HgMnTe-HgTe superlattice structures. These structures also possess variable band gaps over the infrared spectral region. However, this is accomplished by varying the thickness ratio of the constituent layers. The band gap arises from quantum mechanical effects. Because HgTe has a negative band gap, the physical properties of these superlattices are different from those of III-V superlattices. The interest in these materials is considerable. This interest stems from the potential use of device quality Hg-based materials as intrinsic infrared detectors in infrared imaging and communication systems.