The growth and characterization of III-V semiconductor nanowire arrays by selective area metalorganic chemical vapor deposition.

摘要

The interesting properties and potential applications of semiconductor nanowires have received significant attention. Nanoscale selective area growth using MOCVD (NS-SAG) has been demonstrated as an attractive growth technique for compound semiconductor nanowires. With this technique, the diameter and location of wires can be controlled, and no unwanted metal incorporation occurs. This technique is also suitable for large scale uniform nanowire arrays.;Electron beam lithography conditions are optimized to define nano opening arrays for NS-SAG. From this optimization, 25 nm minimum opening diameter and 80 nm center to center spacing features are achieved. InP, GaP, GaAs, and InP nanowire arrays are grown on nano patterned InP (111) and GaAs (111) substrates using NS-SAG. Vertical and uniform InP nanowire arrays are demonstrated on InP (111)A substrates; however, uniform nanowire arrays of GaAs and InAs are achievable only on GaAs and InP (111)B substrates. The surface morphology of InP nanowires is strongly affected by the effective precursor concentration. Enhanced growth in non-polar directions under high precursor concentration disturbs InP nanowire formation. GaAs and InAs NS-SAGs are affected by heterogeneous pyrolysis of arsine and surface diffusion on the sidewalls. The excessive As supply by heterogeneous pyrolysis causes epitaxial burial of nanowires in dense GaAs nanowire arrays and growth rate fluctuations in InAs nanowire arrays. InP nanowires grown in the [111]A direction are in the wurtzite structure at diameters greater than the thermodynamic estimation of the structural transition in diameter. GaAs, InAs, and InP nanowires grown in [111]B direction are in the zincblende structure with rapid stacking fault generation. InAsP and InP/InAs heterostructure nanowire NS-SAG shows the conflict in the preferred growth direction for each binary compound.;A diffusion theory based NS-SAG model is proposed. To reduce the huge computational cost of a vapor phase diffusion simulation of NS-SAG, an average adsorption approximation is proposed. The surface diffusion term is also included to describe the strong diffusion effect induced by the sidewalls. The model predicts the growth rate well, with an average error of 9%, and also predicts a strong surface diffusion effect in GaAs NS-SAG which is consistent with experimental results. The difference of the preferred growth direction, crystal structure transition and stacking fault generation are explained by surface reconstruction of {111} surfaces and the bond strength of III-V and V-V bonds. The presence of the mask and phosphorus trimers, enhances wurtzite stacking of InP nanowires on InP (111)A substrates. GaAs and InAs are prone to grow in [111]B direction because As trimers can be easily dissociated due to weak As-As bonds. Stacking fault generation is also explained by the interaction between surface trimers and adatoms.;Strong artifacts and induced bundling are observed in scanning electron microscopy. By single spot electron beam projection, it is found that the electron beam can pass through the nanowire easily and bundling can propagate along the electron beam path. This induced bundling is explained by attraction between positive charges generated by secondary electron emission and negative charges from the electron beam. From this observation, controlled bundling is demonstrated.