Semiconductor nanowires (NWs) have attracted intensive attention due to both the fundamental physics and their potential applications in optoelectronic devices. GaAs NWs grown by metalorganic chemical vapor deposition (MOCVD) often exhibit tapered and kinked morphologies, depending on growth temperature. However, straight NWs of uniform diameter are preferred for device applications. We have developed a two-temperature growth procedure using MOCVD to simultaneously minimize adatom diffusion, tapering and kinking. GaAs NWs grown by this procedure have shown no planar defects and smooth sidewalls.
Compared with a large amount of studies on GaAs, InP and GaN based III-V NWs, the antimonide III-V NWs have received little attention, despite their great potential for near- and mid-infrared device applications. Very recently, GaSb subwavelength-wire lasers emitting near 1.55 µm have been demonstrated which opened the possibility to use NWs for telecommunications. We report here a successful growth of GaSb/GaAs heterostructure NWs on GaAs (111)B substrate by MOCVD. No misfit dislocations can be observed in the GaSb NW part from HRTEM, which suggests a complete strain relaxation of the GaSb NW on the GaAs NW.
In this talk, I will also talk about the influence of surface passivation on ultrafast carrrier dynamics and terahertz (THz) radiation of GaAs. Since THz emission highly depends on the surface field of the material, surface passivation method was used to prevent the forming of defect states within the semiconductor’s bandgap thus to improve THz related performance. We used 30% (NH4)2S solution to passivate the GaAs sample after the removal of the surface oxide layer. By performing THz spectroscopy and optical-pump terahertz-probe spectroscopy, we observed that the surface electric field of GaAs was reversed after passivation and the conductivity of photoexcited electrons was doubled. Further, the power of the THz emission from large-area photoconductive switches fabricated on passivated GaAs was also enhanced nearly twice. It demonstrates that passivation significantly reduces the surface state density and surface recombination velocity of GaAs, making great influence on the performance of ultrafast THz photonic devices.
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