Theoretical Investigation of Strain-balanced GaP1−xNx/GaAs1−yNy superlattices lattice-matched to Si(001) for 1.5-1.8 eV photonic applications

Abstract

ABSTRACTDilute nitrides alloys of GaP1−x−yAsyNx alloys have attracted much attention since they exhibit a direct bandgap and their lattice constant matches the one of silicon for y=4.7x-0.1. Thus these alloys offer interesting perspectives for the monolithic integration of III-V optoelectronics with the silicon technology. For practically achievable nitrogen composition (x ≤ 0.04), the band gap of GaP1−x−yAsyNx alloys lattice matched to Si is limited to about 1.75 eV. One may attempt to expand the operation wavelength of these dilute nitrides by fabricating a short period strain-balanced GaP1−xNx/GaAs1−yNy superlattices on silicon where ultra-thin layers of GaAs1−yNy (compressively strained) and GaP1−xNx (tensilely strained) are alternated and where the thickness of each layer is maintained to below the onset of the lattice relaxation.In this work we present a theoretical study of the electronic band structure of these strain-balanced (and lattice matched to Si) superlattices in the vicinity of the center of the Brillouin zone (Γ-point). A six-band Kane Hamiltonian modified to account for the strain effect and the band anti-crossing model are used to describe the electronic states of the highly strained zinc blende GaP1−xNx and GaAs1−yNy ternaries. The evolution of the conduction band minima and valence subbands maxima of GaP1−xNx and GaAs1−yNy indicates the occurrence of a type I band alignment for the superlattices involving the mj = ±3/2, ±1/2 valence subbands in the range of compositions of interest.A transfer matrix method has been used to determine the electron and hole minibands of the superlattice structure, predicting the evolution of the band edge transition energies for different nitrogen compositions and alloying/thickness combinations. The results of calculations show the potential to obtain room-temperature photon absorption/emission energies as low as 1.57 eV for a typical nitrogen composition of 5%. The proposed strain balanced structure, thus offers the potential for bandgap engineering ranging from the near IR to visible with host of major applications in silicon-based optoelectronics and multi-bandgap photovoltaics.