Short-Period (GaP1− x N x ) n (GaP1− y As y ) m Superlattices for III-V Solar Cell Integration on Silicon

Abstract (GaP1−xNx)n(GaP1−yAsy)m heterostructures lattice-matched (LM) with Si are interesting for the integration of optoelectronic devices or solar cells (SCs) with standard Si technology. The growth and properties of 50-period (GaP1−xNx)n(GaP1−yAsy)m superlattices that are grown epitaxially on nominally (001)-oriented Si substrates are reported, using gaseous precursors in ultra-high vacuum. These heterostructures are expected to exhibit type-II band alignment because of the addition of N or As to GaP, the former reducing the conduction band energy while the latter increases the valence band energy. Two short-period superlattices with n = 12 and m = 4 monolayers, with different N and As mole fractions are designed and grown, intended to be LM with Si. The results show the high structural quality of these superlattices, with no extended defects such as dislocations, twins or stacking faults observed in the TEM-examined regions. Both samples show intense near-band-edge photoluminescence with room temperature bandgap energies in the range 1.8 to 1.9 eV. The absorption coefficient spectrum exhibits a direct band-like behavior near the absorption edge, approaching to a plateau with values in the range α ∼ 2 × 104 cm−1 above the absorption edge, which are comparable to those obtained for high efficiency SC materials.