spectroscopy and capacitance measurementft lits of ... and capacitance measurementft lits of...
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Spectroscopy and capacitance t f t limeasurements of tunneling
resonances in an Sb-implanted ppoint contact
Nathan Bishop,Sandia National Laboratories
Funded by the Laboratory Directed Research and Development program.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National
Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2010-5581C
Outline• Our design and relation to previous work
Silicon MOS q ant m dots as sensiti e• Silicon MOS quantum dots as sensitive charge sensors
• Donor transport device structure• Comparison between experiment and
capacitive model• Future work – excited state spectroscopyFuture work excited state spectroscopy
and charge sensing• Conclusion• Conclusion
Some previous workTan et al., Nano Lett. 2010
Morello et al., arxiv 2010
Si MOS quantum dots as charge sensorscharge sensors
560400
(Nordberg)
480
520
300
nt (p
A)
curr
ent (
pA)(Nordberg)
400
440
100
200
Dot
cur
ren
oint
con
tact
c
400μV SD
-0.3 -0.2 -0.1 0.0 0.1 0.2360 0
Point contact gate voltage (V)
Po400μV SD
1mV SD
• Reverse normal usage: use a quantum dot to sense changes in a point contact.
• Can be used to sense the spin state of a donor embedded in the point contact.
Si MOS process flowp• Oxide growth• Polysilicon deposition
and patterningOh i t t i l t• Ohmic contact implant and anneal
• Nitride and pre-metal dielectric dep.Sili id d lli i• Silicide and metallization
• E-beam litho and polysilicon patterning
• More EBL and Sb implantation
• Strip metal and re-oxidize polysilicon
• Second dielectric (ALD Al2O3) dep.Al2O3) dep.
• Final metallization
Control sample: Silicon implantp pNo implant
40 keV silicon implant4 x 1011 cm-2 dose
V d
c)
V d
c)X X
bias
(mV
bias
(mVS D
rce-
drai
n
rce-
drai
n
S D
Sou
r
Sou
rS D
Depletion gate voltage (V)Depletion gate voltage (V)
Control vs. implanted_
150nmHAntimony allows
high temperaturepost implant
Sample type Qfb(q/cm2)
Dit(q/cm2eV)
Normal process + 5 x 1010 1 x 1010
Not implantedA G
post-implantprocessing.
100 keV antimony
p
Silicon implant + RTA (Donor device equivalent dose) + 3 x 1011 2 x 1011
Silicon implant + reoxidation + 1 x 1011 1 x 1010
100
2
10-1
Not implanted
BC D E
F
y4 x 1011 cm-2 dose
Silicon implant + reoxidation + 1 x 10 1 x 10
10-2
10-1
ance
(e2 /
h)
10-3
10-2
ance
(e2 /
h)
C D E
10-3
10C
ondu
cta
10-5
10-4
Con
duct
a
-0.8 -0.6 -0.4 -0.2 0.010-4
Depletion gate bias (V)
-0.30 -0.24 -0.18 -0.12 -0.06 0.0010 5
Depletion gate bias (V) T ~ 250mKVsd = 0.5 mVrms
Tunneling spectroscopy-0.30 -0.28 -0.26 -0.24 -0.22 -0.20
Depletion gate bias (V)
dI / dV(S)
H10
52 1E 07
1.0E-06
ias
(mV
) (S)
A G
0
-54.5E-08
2.1E-07
ce d
rain
bi
BC D E
F5
-10
2.0E-09
9.5E-09
Sou
rc
10-2
10-1
/ h)
C D E
Vsd = 50 Vrms 2.0E 09
10-4
10-3
ondu
ctan
ce (e
2
Relevant features:1. Aliasing – nearby charge environment2. Excited states – structure of donors / dots
-0.30 -0.24 -0.18 -0.12 -0.06 0.0010-5
Co
Depletion gate bias (V)
2. Excited states structure of donors / dots3. Slope of lines – capacitance
Capacitive model
Aluminum gate
Si
2DEG
Oxide
SiO2
Polysilicon
2DEG
Al2O3
Harold Stalford, Ralph Young
0.035 Experiment (A or B)
Triangulation of Resonances
0 025
0.030
R=15 nm
R=12.5 nm
Experiment (A or B)Simulated dots (R = 12.5, 15, 18 nm)Simulated donors (depths = 5, 10, 20 nm)
Only dots?
2DEGImplant window
0.020
0.025
1815
R=28 nm
5 to 20 nm donor depth
Top/C
Tota
l Only donors?
Donor atom
0.010
0.015donor depth
40 nm barrier
CT
60 nm barrier
2DEG
0.3 0.4 0.5 0.6 0.70.005
30 nm barrier
CWire+QPC/CS or D H. StalfordP iti d i d t i tiPosition and size determination1. Capacitance ratios are sensitive to small differences
in geometry2. Top gate, S/D and lateral gates cover all three spatial p g , g p
directions- Is resonance below the surface?- Still in progress
Spectroscopy: Sb in SiDeeply buried donor Donor near interface
Ene
rgy
nerg
yRajib Rahman oxide silicon
Position
En
Position
Spectroscopy: excited states9
66
3
mV
)
0
0
C b
ias
(m
Bg B-3 D
C
-6
-9
Bg B21
9-0.22-0.24-0.26-0.28
Depletion gate bias (V)
Conclusions• Fabricated unique device which enables a
id i t f ibl i twide variety of possible experiments.• Identified tunneling resonances in
implanted point contacts, which are rare in clean controls.
• Capacitive measurements locate the resonant states in the point contact, and p ,are consistent with donors as the source.
• Charge sensing measurements ongoingCharge sensing measurements ongoing.
AcknowledgementsQuantum Team:Ed BielejecMalcolm Carroll
Quantum team cont’d:Denise TibbettsLisa Tracy
Kent ChildsKevin EngRobert GrubbsPaul Hines
yJoel WendtWayne WitzelRalph Young
Paul HinesMike LillyJoel MeansRick Muller
Australian collaborators:
Susan AngusEric NordbergTammy PluymRajib RahmanBev Silva
Andrew DzurakWilliam LeeAndrea MorelloMichelle SimmonsBev Silva
Harold StalfordJeff StevensTom Tarman
Michelle SimmonsDan Tomlinson
Greg Ten Eyck
Extracting capacitance-0.20-0.22-0.24-0.26-0.28-0.30
5
Depletion gate bias (V)
4
3
as (m
V)
2
1
rce
drai
n bi
a
0
-1
Sou
r
B A
B peak slopes:-0.2810 417
A peak slopes:-0.2490 277Vsd 0.417 0.277
S D
Vsd
Donor distribution1E21 150 keV Sb implant
SIMS, 121Sb SIMS, 123Sb
1E20 SRIM, 150 keV
n (c
m-3)
1E18
1E19
entra
tion
1E17
1E18
b co
nce
0 300 600 900 1200 15001E16
S
oxide
0 300 600 900 1200 1500
Depth (Å)SIMS by Tony Ohlhausen, SNL
Ion implantation
• E-beam litho and polysilicon patterningSb+
Back end
E beam litho and polysilicon patterning• More EBL and ion implantation• Strip metal and re-oxidize polysilicon• Second dielectric (ALD Al2O3) dep.
i l lli i• Final metallization
Lever arm analysis
measuredBBMAX TkVV
TkE
GG
2cosh
402
eC3.0x10-3 TMC = 19 mK
VSD = 15 Vrms
(e /
h) ModelQuantumlimit (User)
Equationy = A + B * (cosh((x - xc)/ (2*C))) (̂-2)
Reduced Chi-Sqr
2.04899E-9
CeCG
2.0x10-3
ucta
nce
(
Adj. R-Square 0.99476Value Standard Error
West QPC cond A -2.78813E-5 3.98619E-6West QPC cond B 0.00325 2.50309E-5West QPC cond C 0.00227 2.17905E-5West QPC cond xc -0.4295 3.17039E-5
1.0x10-3
nel c
ondu
VTk measuredB
2
-0.50 -0.45 -0.40 -0.350.0
Tunn
0.50 0.45 0.40 0.35
Depletion gate bias (V)Kouwenhoven et al., Electron transport in quantum dots, NATO ASI 1997
Lever arm analysis
A peak ( = 0.0167)
0.8
1.0
ure
(K)
A peak ( 0.0167) B peak ( = 0.0111) Perfect scaling Vds limit = 0.174 K
0.6
mpe
ratu
0.4
sure
d te
m
0.0
0.2
Mea
s
0.0 0.2 0.4 0.6 0.8 1.0
Mixing chamber thermometer (K)
Poor scaling due to high Vdsds
1.8
1 2
1.5
re (K
)
0.9
1.2
mpe
ratu
0.6
aled
tem
A peak ( = 0.165)
0.0
0.3Sca B peak ( = 0.135)
Perfect scaling Vsd limit = 1.16K
0.0 0.2 0.4 0.6 0.8 1.0Mixing chamber thermometer (K)
Top gate lever arm
1.2x10-7
S)A
6.0x10-8
9.0x10-8
ucta
nce
(S
A slope:dVPoly / dVTG = -0.639
B l
0 0
3.0x10-8
6.0x10
Con
d
B
B slope:dVPoly / dVTG = -0.625
H0.0
18.0
18 7 A G
H
-1.5 -1.2 -0.9 -0.6 -0.3Depletion gate bias (V)
18.7 A
B
G
FC D E
Top gate lever arm
Depletion gate bias (V)-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4
18.0
18 1B A
A and B have nearlyidentical top gate lever
18.1
18.2
(V)
arm.There is a disorder dotthat does have a largerlever arm.
18.3
18.4ate
bias
Disorder dot!
18.5
18 6 Top
ga
18.6
18.7
Ion implant damage45 keV silicon implant, equivalent to 100 keV antimony implant
900 C furnace anneal, 24 minutes in O2
Threshold difference
10-4 Leads Control Implanted
10-5
e (S
)
_150nm H
10-7
10-6
nduc
tanc
e
A G
10-8
10 7C
on
BC D E
F
0 3 6 9 12 15 18Accumulation gate bias (V)
C D E
Implant damage increases interface trap density and fixed charge, butp g p y gmostly repaired after high temperature processing.
CV measurements of Dit and Qf by Greg Ten Eyck