Infrared Nonlinear Optics

Contains report on one research project.U.S. Air Force - Office of Scientific Research (Contract F49620-80-C-0008

Tetrahedrally bonded ternary amorphous semiconductor alloys

The properties of tetrahedrally bonded ternary amorphous semiconductors a-CSiSn:H and a-CSiGe:H are reviewed with particular emphasis on the temperature dependence of dark conductivity and the coordination in random networks. It is shown here that the dark conductivity as a function of the temperature strongly depends on the carbon content and, more precisely, on the proportion of sp3 and sp2 sites in the carbon. Ternary alloys with different carbon contents are compared to binary alloys using the average coordination number. The ternary alloys have an average coordination number close to the optimal value predicted for amorphous covalent networks

NEW AMORPHOUS ALLOY SEMICONDUCTORS : a-Si1-xSnx

New amorphous Si1-xSnx alloys have been prepared using a dc cathodic sputtering technic for 0 < x < 0.12. Routine characterization measurements were performed, leading to establish for the first time the existence of these new amorphous semiconductors. Both the average and optical gaps decrease with increasing Sn content, with the latter extrapolating to 0 at x ~ 0.5. The high sensibility of a-Si electronic structure to Sn substitution is discussed in the framework of the tight binding approach, stressing the importance of the atomic relativiste corrections

ELECTRONIC PROPERTIES OF HgCr2S4 IN CONNECTION WITH DEPARTURE FROM STOICHIOMETRY

Des monocristaux du semiconducteur ferromagnétique HgCr2Se4 on été élaborés par transport en phase vapeur. Les monocristaux ainsi obtenus, ou recuits sous Se sont de type p à 300K. Un recuit sous atmosphère de mercure change de manière drastique les propriétés de transport, les échantillons deviennent de type n, le nombre de porteurs et la mobilité augmentent avec la pression de Hg lors du recuit. Ces résultats s'interprètent en admettant que les lacunes de sélénium et de mercure agissent comme donneurs et accepteurs respectivement.Single crystals of the ferromagnetic semiconductor HgCr2 Se4 were grown from the vapor. As grown and Se annealed crystals are p type at 300K. A drastic change of the transport properties appears after Hg annealing, the samples become n type, the number of carriers and the mobility increase with increasing pressure of Hg annealing. The results are understood assuming that Se vacancies act as two charged donors, whereas Hg vacancies atc as acceptors