Semiconductors: a SR approach - ISIS neutron source · Rui Vilão – University of Coimbra...

Rui Vilão – University of Coimbra

Semiconductors: a μSR approach

ISIS muon spectroscopy training school

March/2012

Semiconductors: a SR approach




March/2012

Outline

• What’s the point? H in semiconductors

• Muonium/Hydrogen: the basic Si story

• Beyond Si: Levels, levels, levels

• Other Mu/H related stuff




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Semiconductors: materials with extreme sensibility to the

presence of impurities and defects




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H – common (unavoidable impurity)

Mostly passivating other impurities... ...rarely activating




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When isolated, H is most commonly a compensating impurity




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...but it can be electrically active in some cases




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Muonium: a privileged tool to investigate isolated

hydrogen and, ocasionally, hydrogen complexes

Mu – light pseudo-isotope of H

Not for weak-hearted

particle physicists!




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Isotropic Mu first observed in quartz and germanium...

2-FREQUENCY PRECESSION OF MUONIUM IN A MAGNETIC FIELD

GUREVICH, II; IVANTER, IG; MELESHKO, EA, et al.

SOVIET PHYSICS JETP-USSR 33, 253 (1971)

...and then in silicon

https://webvpn.uc.pt/http/0/apps.isiknowledge.com/full_record.do?product=UA&search_mode=OneClickSearch&qid=5&SID=V1cf7ljDjfeAJHL1ED1&page=1&doc=2&colname=WOS






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10-5

10-4

10-3

10-2

10-1

100

101

102

0,0

0,1

0,2

0,3

0,4

0,5

a23

and a14

a12

and a34

A = 3454.26 M H z

Pre

cess

ion

am

pli

tud

es

B (T )




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Muonium was first identified in Si by longitudinal-field quenching

The spectroscopic measurements had a surprise:




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We now have a rather complete model for Mu/H in Si

For further developments:




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S. F. J. Cox

ISIS Muon Training

Course 2008

Getting the levels…




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Simple ways for determining

the levels

1. Phenomenological Boltzmann functions




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2. Conversion between Mu states: a simple approach




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3. Spin-charge exchange dynamics probed in longitudinal fields




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H/Mu in silicon – a compensating impurity




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…also in Ge and SiGe,…




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…and diamond…




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... and in GaAs, ZnSe, ZnS




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However, in CdS, an hydrogenic state is observed




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...and in ZnO




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ZnO

ZnSe

(+/-)

H behaving as a dopant

(donor)

H behaving as a compensating

centre (amphoteric impurity

always contradicting

conductivity) CG Van de Walle, Phys Stat Solidi (b) 229 (2002) 221




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(+/-) predicted to be

constant

A key to the problem: band line-ups!




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Hydrogen as a source

of conductivity in

oxides

+/- pinning level at 3.0 0.4 eV




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Deep acceptors No muonium is seen Shallow donors

(also In2O3, Ga2O3)

? ? ? Deep donors (Ag2O and

HgO, not represented)

? ?




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Shallow donor hydrogen in

transparent conductive oxides




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Oxides: the devil hides in the details




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Oxides: the devil hides in the details

Y2O3 E. Silva et al.,

arXiv:1106.5032v1 [cond-mat.mtrl-sci], 2011.




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Other stuff: I. Muon diffusion and defect/impurities passivation




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Other stuff: II. An organic glimpse




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Other stuff: III. Electron spin polarization




March/2012

Semiconductors: a SR approach - ISIS neutron source · Rui Vilão – University of Coimbra...

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