13:15 〜 13:30
▲ [15p-421-1] Novel crystalline behaviors of self-catalyst GaAs nanowires on GaAs(001) substrates with thin film masks by molecular beam epitaxy
キーワード：One-dimensional GaAs semiconductor, molecular beam epitaxy growth
One-Dimensional (1D) semiconductors have been developed over the last two decades into a large field and they are believed to be building blocks for wide range of applications. III-V group semiconductors are well-known materials with high electron mobility and conductivity that are important for future high-speed and low-power nanoelectronics [1]. Here we present in detail of self-catalyst GaAs nanowire (NW) growth on hydrogen silsesquioxane (HSQ)-coated GaAs(001) substrate using molecular beam epitaxy (MBE).
After coating and annealing of HSQ in the air, substrate surfaces were uniformly covered with 20-nm-thick SiOx which could open pin-holes at the beginning of the growth [2]. Surface treatment is particularly important for NW growth and usually follows complicated procedures. In this work, Ga exposure in 20 s on HSQ-coated substrates without As flux was performed to create NW nucleation sites i.e. Ga nanoparticles. The typical growth condition is as follows; Ga beam equivalent pressure (BEP) of 5.4x10-8 Torr (growth rate of 0.04 ML/s on planar), As BEP of 1.0x10-6 Torr (V/III ratio of 18.5), and growth temperature of 620 oC.
Figure 1(a) shows top-view scanning electron microscope (SEM) image of NWs after 4-hour growth. To remove Ga nanoparticles at top of NWs, the NWs were kept in As flux of 2.0´10-6 Torr at 500 oC for 1 hour without Ga flux. The obtained NWs were found to project on substrate to form approximately 35o and 73o with their own projections <1-10> and <110>, as shown in Figs. 1(b) and 1(c). We also observe that the NWs’ cross sections of the all directions show hexagonal shape indicating <111> orientations. 35o NWs along <1-10> are observed to be predominant and attributed to <1-11>B orientations. 35o NWs pointing along <110> is also evaluated to be <1-11>B derived from inverse polarity of crystal through thin and non-polar native oxide layer on substrate. 73o NWs were observed to be <1-11>B which are formed through on-substrate rotation of <1-11>B by 60o around <111>A. The tendency for 60o rotation around <111> on single NW was observed through TEM analysis which enables twin plane formation.
After coating and annealing of HSQ in the air, substrate surfaces were uniformly covered with 20-nm-thick SiOx which could open pin-holes at the beginning of the growth [2]. Surface treatment is particularly important for NW growth and usually follows complicated procedures. In this work, Ga exposure in 20 s on HSQ-coated substrates without As flux was performed to create NW nucleation sites i.e. Ga nanoparticles. The typical growth condition is as follows; Ga beam equivalent pressure (BEP) of 5.4x10-8 Torr (growth rate of 0.04 ML/s on planar), As BEP of 1.0x10-6 Torr (V/III ratio of 18.5), and growth temperature of 620 oC.
Figure 1(a) shows top-view scanning electron microscope (SEM) image of NWs after 4-hour growth. To remove Ga nanoparticles at top of NWs, the NWs were kept in As flux of 2.0´10-6 Torr at 500 oC for 1 hour without Ga flux. The obtained NWs were found to project on substrate to form approximately 35o and 73o with their own projections <1-10> and <110>, as shown in Figs. 1(b) and 1(c). We also observe that the NWs’ cross sections of the all directions show hexagonal shape indicating <111> orientations. 35o NWs along <1-10> are observed to be predominant and attributed to <1-11>B orientations. 35o NWs pointing along <110> is also evaluated to be <1-11>B derived from inverse polarity of crystal through thin and non-polar native oxide layer on substrate. 73o NWs were observed to be <1-11>B which are formed through on-substrate rotation of <1-11>B by 60o around <111>A. The tendency for 60o rotation around <111> on single NW was observed through TEM analysis which enables twin plane formation.