C. Gutsche, I. Regolin, F.J. Tegude, W. Prost
D. Stichtenoth, K. Wegener M. Seibt, C. Ronning
Semiconductor nanowire may form building blocks for future nanoscale devices. However, applications in electronics and photonics requires effective and controlled doping which is difficult to realize in the typical vapor-liquid-solid-growth mode. In this contribution, the electrical and structural characterization of nanowires prior and after implantation is presented.
Gallium arsenide (GaAs) nanowires with diameters of
150 nm have been grown via metal-organic vapor deposition on (100) oriented s. i. GaAs substrates. The preferred growth orientation along the <111>B orientations provide an optimum angle for a subsequent ion implantation. Ion implantation of 64 Zn and 32 S was performed at room temperature. Multiple ion energies up to 450 keV and ion fluencies of up to 1•10 15 cm -2 were used, in order to create a homogeneous box-like concentration profile with a projected ion range matching the wire diameter. Structural characterization of the wires prior and after ion implantation has been carried out by
TEM investigations.
After high dose ion implantation the dark-field image of the surface of the nanowires facing the ion beam is amorphous, while a remaining crystallinity preserved on the far side. After annealing in the MOVPE at 800°C under group-V overpressure for 30 minutes, all nanowires are fully recrystallized. However, a dislocation of about i.e. ~ 5•10 9 cm at 1•10 15 cm -2
.
2 is observed in case a of 64 Zn implantation
The electrical properties of the 64 Zn implanted nanowires are presented in Fig. 2. The nanowires were scratched-off the growth substrate and deposited on top of
GaAs substrates covered with a 250 nm thick insulating
Si
3
N
4
layer for electrical isolation. A transmission line pattern is used in order to determine both, the wire and the contact resistance, respectively. The as-grown GaAs nanowires exhibit a resistance of about 0.5 G

. Ion beam doping and subsequent annealing lead to a current flow of about 80

A and a very low resistance of 25 k

The contact resistance of the Pt/Au type contact on GaAs:Zn nanowires is about ~7,5 k

.
The carrier concentration was determined assuming a surface depletion due a GaAs surface potential of V
S
~
0.5 V and a concentration dependent hole mobility. Under these assumption the hole concentration of p ~ 3.5•10 18 cm -3 is calculated for our p-type GaAs:Zn nanowire.
Based on the same model, the carrier concentration for the undoped sample is calculated to N
A
< 2•10 17 cm -3 .
These investigations show that ion implantation is a powerful tool for controlled doping of GaAs nanowires.
Finally, a continued growth of the nanowire after annealing will be presented, proving the high crystalline quality and opening-up new possibilities for heterostructure growth and device fabrication.
80
(c)
Figure 1: Dark field TEM images and corresponding diffraction patterns of selected areas of GaAs nanowires after Zn implantation and prior to annealing.
40
0
-40
-80
(a), (b)
10
-2 -1 0 1 2
(a)
5
0
(b)
-5
-10
-2 -1 0 1 2
Figure 2: I-V characteristics of GaAs nanowires (a) as grown, (b) after annealing, and (c) after ion doping. The upper inset shows the used transmission line pattern.