Highly Enriched 28Si – new frontiers in semiconductor spectroscopy
M. L. W. Thewalt , A. Yang, M. Steger, T. Sekiguchi, K. Saeedi,
Dept. of Physics, Simon Fraser University, Burnaby BC, Canada V5A 1S6
T. D. Ladd, E. L. Ginzton Laboratory, Stanford University, Stanford CA, USA (now HRL)
K. M. Itoh, Keio University, Yokohama, Japan
H. Riemann, N. V. Abrosimov, IKZ, Berlin, Germany
Avogadro
Project
A. V. Gusev, A. D. Bulanov, ICHPS, Nizhny Novgorod, Russia
A. K. Kaliteevskii, O. N. Godisov, “Centrotech-ECP”, St Petersburg, Russia
P. Becker, PTB, Braunschweig, Germany
H.J. Pohl, VITCON Projectconsult GmbH, Jena, Germany
J. J. L. Morton, Oxford, UK
S. A. Lyon, Princeton, USA
SILICON – 2010
Nizhny Novgorod
Natural Si:
92.2% 28Si + 4.7% 29Si + 3.1% 30Si
I=0
I=½
I=0
Why does the isotopic composition affect electronic and optical properties?
the electron-phonon interaction
E
bare EG
ΔE
actual
EG
~62 meV for natSi
The renormalization goes as M -1/2
EG depends
recent review:
on M due to
Cardona and Thewalt
zero point
motion
0
T
Reviews of Modern Physics 77,
1173 (2005)
R.T.
Eg(0) increases by ~2 meV from 28Si to 30Si
The spectroscopic challenge of highly enriched 28Si
D. Karaiskaj et al., Phys. Rev. Lett. 86, 6010 (2001) [ FWHM < 0.005 cm-1 ]
Boron BE
B
1
1
a
Photoluminescence Intensity
PNPBE
NP
T=1.3 K
natural Si
28
Si
9275.0
9280
9281
-1
Photon Energy for natural Si (cm )
( 8 cm-1 ~ 1 meV )
Boron BE
200 neV !
Improved shallow bound exciton linewidths – observation of the 31P
ground state hyperfine splitting in the donor bound exciton transition.
Phys. Rev. Lett. 97, 227401 (2006). Nuclear and electron spin readout…
31P
prime Si
qubit
candidate
a
can we use
this to
polarize the
spins?
Initialization
problem
Hyperpolarization
using optical pumping
Phys. Rev. Lett.
102, 257401 (2009)
Almost zero equilibrium
polarization
Resolved bound exciton hyperfine spectroscopy gives the populations
of all four donor hyperfine levels in a single measurement
Nuclear polarization of 76% and electronic polarization of 90% are
achieved simultaneously – in less than 1 second!
Higher polarization should be possible with reduced linewidths
New experiments: NMR on dilute 31P in 28Si using optical polarization
and optical nuclear spin readout
CW NMR
PL intensity
pump 8, probe 10
RF power: -75dBm (40 µV)
B = 844.77 G
FWHM = 24 Hz
55,846,700
RF frequency (Hz)
55,846,750
Why 845 Gauss?
Schematic energy diagram
e, 31P
Energy (nonlinear)
844.9G
34,043G


Max.
55.85 MHz
A
A = 117.53 MHz
Min.
61.68 MHz


Magnetic field (nonlinear)
ge =
1.99850
g31P =
2.26320
Magnetic Field Dependence
61,677.25
f0=61,677.172 kHz
B0=844.85 G
RF frequency (kHz)
61,677.20
e: probe 4, pump 6
RF: -75 dBm (40 µV)
61,677.15
55,846.75
e: probe 10, pump 8
RF: -75 dBm (40 µV)
55,846.70
f0=55,846.712 kHz
55,846.65
B0=844.89 G
840
845
Magnetic field (Gauss)
850
transient NMR - Rabi Oscillations
PL Intensity
RF: CW 15 dBm (1.26V) at 55,846,714 Hz
pump 8, probe 10
lasers always on
0.0
0.5
1.0
Time (ms)
1.5
2.0
First pulsed NMR Ramsey Fringe Experiment
signal
on (polarizing)
measurement
Lasers
off
on
p/2
p/2
RF pulses
off
t
RF freq. = Resonance freq. +/– 1 kHz  fringes of 1 kHz
Ramsey Fringes
Temperature (Pressure) dependence
PL intensity
Pump 8(), Probe
10(), ; RF Hz
= 55,847,712 Hz;
RF=55,847,712

T=4.2K (P=1atm)
fRamsey = 2,453.6 Hz, T2* = 21.0 ms
RF

pump


T=1.3K (P=1.0Torr)
fRamsey = 975.4 Hz, T2* = 16.4 ms
0
10
20
t (ms)
30
probe
31P
Donor Hyperfine Constant
 At T=1.3K (P=1.0Torr)
me


RF freq.
(Hz)
Fringe freq.
(Hz)
55,845,712.0
1,024.9
55,847,712.0
975.4
Σ = 2,000.3
61,676,172.0
1,027.2
61,678,172.0
972.9
Σ = 2,000.1
NMR freq.
(Hz)
55,846,736.8(1)
61,677,199.1(1)
 Hyperfine constant A = 117.523 935 9(2) MHz at T=1.3K
[existing value 117.53(2) MHz]
 At 4.2 K and 1 atm, A is 3.116 kHz (26.5 ppm) lower!
Why?
Pulsed NMR
—Hahn echo method—
PL signal
on
measurement
(initialization)
Lasers
(Pump&Probe)
off
on
p/2
p/2
p
rotation for optical readout
RF pulses
off
t
t
refocusing
fRF = fNMR
Signal decay with 2t  measurement of T2
T2 from Hahn Echo Method
Pump
6(),
Probe 4(); RF = 61,677,199 Hz;
Hahn
echo
result:
B =pump
845.3
G, T =4,1.3
(P =G,
1.0
Torr)
61,677,199 Hz,
845.3
G,
= 1.3
1.3 K
K (P
(P == 1.0
1.0 Torr)
Torr)
6, probe
B =K845.3
TT =
1000
intensity
PLamplitude
T22 =
= 250
250 ms
ms
T


pump
100
probe

10
0
500
(ms)
22t tau
(ms)
1000
1000

RF
Highly Enriched 28Si – new frontiers in
semiconductor spectroscopy
Resolved donor bound exciton hyperfine structure:
- optical readout of 31P electron and nuclear spin
- fast optical hyperpolarization of electron and nuclear spin
- possibility of single donor readout
- promising new approaches to silicon quantum computing
- have begun NMR of 31P in 28Si combining optical readout and
optical hyperpolarization
Studies which were thought to be limited to isolated single atoms and ions
in vacuum are now becoming possible in semiconductors.