Role of surface energy on the morphology and optical properties of GaP micro & nano structures grown on polar and non-polar substrates

• Published in: Applied surface science 2017-10, Vol.419, p.957-967
• Main Authors: Roychowdhury, R., Kumar, Shailendra, Wadikar, A., Mukherjee, C., Rajiv, K., Sharma, T.K., Dixit, V.K.
• Format: Article
• Language: English
• Subjects: GaP micro & nano structures; High resolution x-ray diffraction; Polar and non-polar substrates; Surface energy; Ultraviolet photoelectron spectroscopy; Valence electron plasmon
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.05.026

[Display omitted] Epitaxial structures of III-V and III-V-N compound semiconductors on Si and Ge has been the focus of extensive research because of their numerous applications. Among all the III–V semiconductors GaP having a wide band gap and low lattice mismatch with Si is considered to be one of the prime candidates for high efficiency multi-junction solar cells. However, formation of micro-twins and anti-phase boundary hinders the integration of high device quality of GaP epilayer on Si. In this work the role of surface energy on the morphology, crystalline quality, electronic structure and optical properties of GaP layer grown on Si (001), Si (111), Ge (111) and GaAs (001) is investigated. GaP layers are grown on polar and non polar substrates under identical growth kinetics by MOVPE. The AFM images show that GaP layer completely covers the surface of GaAs substrate. On the other hand, the surface of Si (001), Si (111), and Ge (111) substrates is partially covered with crystallographically morphed GaP island type micro and nano-structures leading to surface modifications. Origin of these surface modifications is explained by the theoretical calculation of surface energy of the layer and corresponding substrates respectively. The nature of GaP island type micro and nano-structures and layers are single crystalline with existence of rotational twin on Si(111) substrate which is confirmed by the phi, omega and omega/2theta scans of high resolution x-ray diffraction. The electronic valence band offsets between the GaP and substrates with their corresponding band alignment has been determined from the valence band spectra of photoelectron spectroscopy. Effects of the surface morphology on the valence electron plasmon are investigated by studying the energy values of core level loss peaks in the energy dependent photoelectron spectra. The peak observed within the range of 3–6eV from the Ga (3d) core level in the photoelectron spectra of GaP are related to inter band transitions and their significance is also observed in the energy dependent pseudo dielectric function estimated from the spectroscopic ellipsometry. The bandgap of micro and nano structures are also estimated from the onset of the loss peak of Ga (3d) associated with interband transition of GaP. •Crystallographically morphed GaP micro & nano-structures and layer are grown on polar and non polar substrates under identical conditions by using MOVPE.•The topological variations of the epitaxial str