BAND-GAP AND HETEROJUNCTION DISCONTINUITIES OF PSEUDOMORPHIC SI1-X-YGEXCY ALLOY LAYERS ON SI(001)

We present a theoretical study of the minimum band gap of the pseudomo rphic Si1-x-yGexCy ([C] less than or equal to 9%) alloy layers grown o n Si(001). We also investigate the valence-band offset and conduction- band offset at the strained Si1-x-yGexCy /Si(001) heterointerfaces, in the framework of the average bond energy theory in conjunction with t he deformation potential method. Self-consistent calculations are base d on the local density functional theory, ab initio pseudopotentials a nd the virtual-crystal approximation. Our results show the correct ten dency and order of magnitude compared with most of the theoretical and experimental data. It is encouraging to find that the tendencies of t he minimum band gap and band offsets with the alloy composition and la ttice mismatch are changed suddenly at the critical point due to the d ifference of the strain properties at the two sides of zero lattice mi smatch. Our results also indicate that it is possible to obtain a larg er conduction-band offset of the Si1-x-yGexCy/Si(001) heterostructure than that of the Si1-xGex/Si(001) heterostructure which offers a new p rospect for the development of heterostructure devices compatible with Si integrated circuit technology. (C) 1998 American Institute of Phys ics. [S0021-8979(98)07715-9].