Selective area epitaxy of GaP nanowire array on Si (111) by MOCVD

Because of its indirect bandgap nature, Gallium phosphide (GaP) in its conventional zinc blende crystal structure, has only limited optoelectronic applications in the visible light spectrum. The WZ structured GaP, on the other hand, has a direct band gap between 2.18 and 2.25 eV, ideal for a green-yellow spectral range light emitting devices. It is well known that the crystal structure of the III-V materials can be modulated when they are grown in nanowire (NW) form via the VLS/SAE mechanism so that either a ZB, WZ, or an intermixing of the ZB and WZ structured III-V NWs can be achieved. The realization of WZ GaP NWs were experimentally verified but the mechanism of selecting a crystal structure while NW is grown are still controversial. However, a common factor that promotes the realization of WZ structured NW is the suppression of the lateral overgrowth, because the ZB structure has the lowest surface energy at {11
^-
0} side facets of the hexagonal NW. On the other hand, the nucleation at side {11
^-
00} facets of WZ NW is difficult so that the hexagonal WZ NWs tend to grow more vertically with less lateral overgrowth. Understanding, developing, and controlling the growth condition of GaP NWs to form WZ structures would be crucial to practical applications of this highly promising material system. In addition, integrating GaP on silicon is also challenging. Recently, GaP nanowire (NW) heteroepitaxial growth have been demonstrated on Si (111) and Si (100) substrates using the VLS method. However, selective area epitaxy (SAE) of GaP NWs on Si (111) substrate or even on the GaP (111) substrate have not been well developed yet.