Low Energy Ion Irradiation Effect on Electron Transport in Gaas/Algaas Heterostructures
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1Onim Si-doped GaAs Ion Energy IkeV
60nm Si-doped AIGaAs
20nm undoped A2GaAs
td...o....
--
Si+ Ar'
2DEG0 800nm undoped GaAs
:. 0
S
Fig.1.
5 Depth [nm]
G~eubtae0
10
Fig.2. Distribution profiles of
Schematic view of the
1 keV Si and Ar ions in AlGaAs
calculated using TRIM code.
GaAs/AlGaAs heterostructure sample used in this experiment.
EXPERIMENT The GaAs/AlGaAs heterostructure used in this experiment was grown by MBE, and has a structure as shown schematically in Fig.1. It has a 2DEG at the GaAs/AlGaAs hetero interface 90 nm below the surface. Carrier density and electron mobility of asgrown samples were 2.4 X 1011 cm- 2 and 3.0 x 105 cm 2/Vs, respectively, at 1.5 K in the dark. After the samples were deeply mesa-etched to a Hall bar pattern, and conventional AuGe/Ni/Au Ohmic contacts were formed, a 1 keV unfocused Ar ion beam was irradiated at room temperature on the whole area of the sample surface at doses of 1011, 1012 and 1013 cm-2. As shown in Fig.2., the distribution profiles of 1 keV Ar and Si in AlGaAs, which were estimated by using TRIM code, are almost the same. Although there exists a little difference between them and the chemical effect of these ions in AlGaAs substrates may be different from each other, the ion irradiation-induced damage by collision cascades might be similar. Therefore, we used Ar ions to estimate damage effect. Carrier density and electron mobility of Ar ion irradiated samples were estimated at 1.5 K by Hall resistance and longitudinal resistance measurements before and after annealing at 400 'C for 10 min in an Ar gas ambient. The temperature dependence of those values was also measured for as-grown and for 10i3 cm-2 ion irradiated and subsequently annealed samples. RESULTS AND DISCUSSION Fig.3. shows the dependence of the carrier density and the electron mobility on a (a) 20 eV and (b) 1 keV Ar ion dose before and after annealing. In the case of the 1 keV Ar ion irradiation, the carrier density was almost independent of the ion dose ranging from 10 "1 to 1013 cm- 2 and showed almost the same value as the as-grown sample. The mobility of the as-irradiated (i. e., before annealing) sample was slightly decreased with increasing the ion dose. This decrease in mobility was much less than in the case of the 20 and 300 eV
166
d9-'(a) 20eV Ar+ 10
E C.,~
0
. 105 ý, 102
A.I
01
10 16
1015 Dose (cm -2 )
"..Ib Ml1keV Ar+ o as-irradiated S106 Aannealed at 400 0C, 10 min
E
-e
0
p
•
,
•-
,-
- ,
-
,
--
,
,
105 Cý 101-
E
Fig.3. Dependence of carrier density and electron mobility on (a) 20 eV (from reference 7) and (b) 1 keV Ar ion dose, measured at 1.5 K
a,
0)
10
1 44
10 1
10 ~013
1012 Dose (cm -2)
167
in the dark. Arrows in (b) show the values of the asgrown sample.
".4
Cli-
o
0
io4
A'
E
00
dark condition o & as-grown
o
irradiated
C "
*
4
11
Z
2 rr rr
-0 < 100
10
TEMPERATURE (K) Fig.4. Temperature dependence of carrier density and electron mobility of asgrown and 1 keV 1013 cm- 2 Ar ion irradiated and subsequently anneal
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