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Research On Doping Of ?-? Semiconductor Nanowires And Their Applications In Photodetectors

Posted on:2017-09-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:J S LiFull Text:PDF
GTID:1318330518996009Subject:Electronic Science and Technology
Abstract/Summary:PDF Full Text Request
In recent years, semiconductor nanowires as a whole have become a hot topic in information materials due to their tiny radial size, structure induced large tolerance in hetero-integration, and novel physical properties. III-V nanowires are promising in novel low-consumption,high-speed, high-sensitivity, and high integration nano optoelectronic devices due to their advantages of direct bandgap and high electron mobilities compare to traditional material, Si, used in integrated electronics. The present thesis focuses on key fabrication technologies of nanowire optoelectronic devices. The main contributions are as follows:(1) Si and Zn are used as donor and acceptor impurities to realize insitu n-type and p-type doping of GaAs nanowires during growth via metal organic chemical vapor deposition (MOCVD). It is found that the incorporation of Si barely affects the growth rate or structure of GaAs nano wires. The incorporation of Zn slightly enhances the growth rate of GaAs nanowire, while excess Zn causes cracking of the Au-Ga alloy drops which acts as catalyst and kinking of nanowires. Effective p-type doping GaAs nanowires can be realized by the incorporation of Zn, and a high doping density of 1019 cm-3 can be achieved with a II/III ratio of 0.012. On the contrary, the incorporation of Si can hardly realize n-type doping of GaAs nano wires since Si acts as both donor and acceptor in GaAs. For example, under a high IV/III ratio of 1.377, the doping density is only 1017cm-3 . As excess impurities would significantly degrade the carrier mobility, other elements should be considered as donor dopant instead of Si.(2) The fabrication technologies of a single n-type GaAs nanowire photoconducor are explored. A single n-type GaAs nanowire ohmic photodetector is fabricatedvia choosing Ti as the contact material, which has a proper Fermi energy, and passivating the contact area to improve the contact performance. The responsivity firstly increases and then decreases as the illumination intensity increases, and the highest responsivity is 1.58×10-3 A/W under 2000 W/cm~2 illumination of a 532 nm laser at 5 V bias.(3) Unintensionally-doped tapering InAs nano wires are grown by Au-catalyzed MOCVD, and a single InAs nanowire photodetector is fabricated. The device exhibits an anomalous photoconductive property.Under low-power illumination, the current is smaller than the dark current, and monotonously decreases as the excitation power increases.When the excitation power is high enough, the current starts to increase.The negative photoconductive property is attributed to the difference in carrier mobilities along the nanowire radius due to the surface states. As the illumination increases,the "core current" quickly decreases and the"shell current" slowly increases, resulting in a first decrease and then increase phenomenon of whole current.(4) Axial and radial GaAs nanowire pn junctions are grown based on the research on n-type and p-type doping of GaAs nano wires. GaAs nanowire array diodes are fabricated based on the pn junctions, which exhibit obviously rectified behavior. A prototype solar cell is fabricated based on the radial nanowire pn diodes, which exhibits obviously photovoltaic properties. However, the performance of the cell is not ideal due to the low doping density of n-type GaAs nanowires as well as the incomplete contact between the electrode and nanowires.
Keywords/Search Tags:nanowire, Metal Organic Chemical Vapor Deposition (MOCVD), doping, photodetector, solarcell
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