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