Band structure and absorption properties of (Ga, In)/(P, As, N) symmetric and asymmetric quantum wells and super-lattice structures: Towards lattice-matched III-V/Si tandem

Abstract

Quaternary dilute nitride compound semiconductors like GaAsyP1−x−yNx and Ga1−zInzP1−xNx are lattice matched with silicon when y = 4.7 * x − 0.1 and z = 2.2 * x − 0.044 and also have direct bandgaps (with N > 0.6%), thus allowing for monolithic integration of III-V optoelectronics with silicon technology as well as III-V/Si tandem junction solar cells. By applying an eight-band k.p strained (tensile or compressive) Hamiltonian and a Band Anti-crossing model (to account for small amounts of nitrogen impurities) to the conduction band, the electronic band structure and the dispersion relation of these alloys can be determined near the center of Brillouin Zone. In this work, by minimizing the total mechanical energy of the stack of alternating layers of GaP1−xNx and GaAs1−xNx, we have evaluated the ratio of thickness of the respective layers for a strain-balanced superlattice GaAs1−xNx/GaP1−xNx structure on silicon. We calculated the confinement energies and the corresponding states of the respective carriers inside a quantum well (with and without resonantly coupled) or in the miniband of a superlattice structure as a function of the nitrogen composition using a transfer matrix approach under the envelope function approximation. Incorporating only a small amount of nitrogen (<5%), the bandgap of these lattice matched structures fulfils the optimum bandgap requirement of (1.65–1.8) eV for III-V/Si tandem solar cells and optoelectronic devices. The optical-absorption coefficient, in both symmetric and asymmetric quantum wells, is then evaluated with respect to nitrogen composition and temperature by using the Fermi-golden rule for both TE and TM polarization of incident light, including the effect of excitons and thermal broadening.