| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
J8, Electrical Properties of Axial and Radial Nanowire pn-Junctions – A Comparison
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| Author(s) |
Christoph Gutsche, Andrey Lysov, Ingo Regolin, Werner Prost, Franz-Josef Tegude |
| On-Site Speaker (Planned) |
Christoph Gutsche |
| Abstract Scope |
III-V semiconductor nanowires hold the promise to act as key element e.g. in next generation photovaltic (PV) devices due to their possible higher conversion efficiencies compared to thin film devices combined with the ability to use relatively inexpensive silicon substrate material. Currently, it is under discussion whether axial or radial pn-junctions are more target-aimed. The latter allows an optimal light absorption and an effective light collection but the shell growth is restricted to the similar strain considerations as thin films. In contrast the first enables the creation of multijunction PV with a relative small absorption area.
Here we will present and compare the electrical properties of axial and radial nanowire pn-junctions. Both, axial and radial junctions are formed by Au assisted vapour-liquid-solid MOVPE growth on (111)B GaAs substrates. Radial pn-diodes were formed between n-doped GaAs nanowire core (n ~ 1•10<SUP>18</SUP> cm<SUP>-3</SUP>) with a diameter of 100 nm and 100 nm thick p-doped GaAs shell (p ~ 3•10<SUP>18</SUP> cm<SUP>-3</SUP>). An additional 30 nm thick nominally undoped InGaP region was inserted into the structure to allow selective wet etching of the outer shell. Details of axial GaAs pn-junction growth can be found elsewhere. The as-grown structures were transferred to special pre-patterned carriers and finally contacted by electron beam lithography and lift-off technique. Ohmic contacts were obtained using Ge/Pd/Au as n-contact system and Pt/Ti/Pt/Au as p-contact system, followed by subsequent rapid thermal annealing for 30 s at 280°C and 360°C, respectively. The growth, basic process scheme, doping profiles, and electronic properties of both diode types will be presented, compared and discussed with respect to possible applications. The unique strength of axial pn-junctions is the ultra-low reverse current giving rise to an on/off ratio of about 10<SUP>6</SUP>. Radial nanowire diodes exhibit a worse reverse current and higher forward current because of the larger area of the junction region. The lower diffusion voltage of radial pn-junctions as compared with axial structures (0.5 V and 1 V respectively) is also observed in other works and fits to first numerical simulations of other groups. It is attributed to defect states at the contact/semiconductor interface as well as between the nanowire shells.
In conclusion, radial as well as axial high current single GaAs nanowire pn-diodes are demonstrated. The comparison shows that there is high potential for device optimisation in terms of doping profiles, junction abruptness and surface passivation. |
| Proceedings Inclusion? |
Undecided |