the role of n-h complexes in the control of localized center...

Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html

The role of N-H complexes in the control

of localized center recombination in

hydrogenated GaInNAsN. J. Estes1, M. Fukuda1, V. R. Whiteside1, B. Wang2 , C. R. Brown1,

K Hossain3, T. D. Golding3, M. Leroux4, M. Al Khalfioui4, J. G.

Tischler5, C. T. Ellis5, E. R. Glaser5, and I. R. Sellers1

1 Department of Physics & Astronomy, University of Oklahoma, Norman, OK 73019, USA2 School of Biological, Chemical, and Materials Engineering, University of Oklahoma, OK 73019, USA

3 Amethyst Research Inc., 123 Case Circle, Ardmore, OK 73401, USA 4 CRHEA-CNRS, Rue Bernard Gregory, Valbonne 06560, France

5 US Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375, USA


Multijunction Solar Cells:

Divide and Conquer

• Three junctions: 44% efficient

• Four junctions: Up to 52% efficient

• Power wasted by Ge due to poor current matching

We need a material with 1eV band gap,

correct lattice spacing

http://www.pvmeasurements.com/

J.F. Geisz and D.J.Freidman, Semiconductor Science and Technology 17, 769 (2002)


GaInNAs is a Promising but Problematic

Candidate for the Fourth Junction

Growth Problems:

• High temperature--

phase separation,

clustering

• Low temperature--

defect formation,

low nitrogen inclusion

Regardless of sample quality, substitutional N is

locally different electrically than As, causing low

diffusion lengths.

J. S. Harris, Semicond. Sci. Technol. 17, 880 (2002)


Effects of Annealing

Post – growth annealing improves material quality

• Ga-vacancies removed

• N – As exchange increase nitrogen incorporation

• Low temperature PL dominated by localization centers

Effects observed in the performance of GaInNAs solar cells

1060 1080 1100 1120 1140 1160

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As-Grown

Inte

nsit

y (

arb

. u

)

Wavelength (nm)

RTA 830°C


Hydrogenation Has Shown Passivation

of Substitutional Nitrogen

• Restoration of original band gap

• Process reversible through

annealing

• Favorable due to small,

electronegative nitrogen

Polimeni et al. Semi. Sci Tech. 797, (2002)

Bissiri et al. Phys. Rev. B. 65, 235210 (2002)

Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html 6

Selective Defects Passivation

in Solar Cell Materials

PUMP

Lamp 1

Lamp 2

Loadlock

• UV-activated hydrogenation – Deuterium based

• Typical 100 °C – 350 ° C

• Pressures ranging from 10-6 – 105 Torr


Passivation in Solar Cell

0 60 120 180 240 300

1.12

1.14

1.16

1.18

Reference

Peak E

nerg

y (

eV

)

Temperature (K)0 60 120 180 240 300

1.12

1.14

1.16

1.18

Lowest Hydrogenation

Peak E

nerg

y (

eV

)

Temperature (K)0 60 120 180 240 300

1.12

1.14

1.16

1.18

Highest Hydrogenation

Peak E

nerg

y (

eV

)

Temperature (K)

1040 1060 1080 1100 1120

1050 1075 1100 1125

Reference

Inte

nsit

y (

arb

.u.)

Wavelength (nm)

170K --> 290K

1040 1060 1080 1100 1120

1050 1075 1100 1125

Lowest Hydrogenation

Inte

nsit

y (

arb

.u.)

Wavelength (nm)

170K --> 290K

1040 1060 1080 1100 1120

1050 1075 1100 1125

Highest Hydrogenation

Inte

nsit

y (

arb

.u.)

Wavelength (nm)

170K --> 290K

Proc. 40th IEEE PV Specialists, Denver 2014


Solar Cell Characterization

• Increase in performance of the solar cell after hydrogenation

• No visible effect on the substitutional Nitrogen – selective passivation

Fukuda et al. Applied Physics Letters 106, 141904 (2015)


Samples Used

-Bulk Ga0.91In0.09N0.028As0.972

grown via MBE using RF plasma

source for nitrogen

-annealed at

800°C for 30s

UV-Activated

hydrogenation,

2 μm penetration

Three samples:

• Reference – Unhydrogenated

• #9 – Intermediate hydrogenation

• #8 – High hydrogenation


Hydrogenation of GaInNAs Mitigates

Localization Effects, Retains Band Gap

Reduction in intensity of low-energy “shoulder”

Localized

Exciton emissionBand GapLocalized

Exciton emission

Band Gap


Hydrogenation of GaInNAs Mitigates

Localization Effects, Retains Band Gap

Peak now has reduced ‘s-shape’ with temperature

1000 1050 1100 1150 1200

Reference PL by T

Inte

nsit

y (

Arb

. U

.)

Wavelength (nm)

1000 1050 1100 1150 1200

Hydrogenated (#8) PL vs T

Inte

nsit

y (

Arb

. U

.)

Wavelength (nm)


•Individual Peaks EG, EL, and ED are tracked and intensities are fitted

•k(I α Pk)

•k < 1 - Defect/localized states

•1 < k < 2 - Band to band recombination


Selective Passivation: Effect of excitation

intensity

Reference - unhydrogenated Hydrogenated – 1 x1015 cm-2

Acknowledgement: Joseph Tischler and Chase Ellis


• Supercell of 64 atoms used

• 29 Ga, 32 As, 3 In

• 1 N replaces an As atom for

GaInNAs, giving 3% Nitrogen

• As Hydrogen concentration

increases Ga-H2-N complexes form.

The feature related to nitrogen is

pushed into the continuum.

However the scattering center still

remains.

Density Functional Theory Results

Acknowledgement: Dr. Bin Wang – CBME, University of Oklahoma


Further Testing of Samples is Needed

• Annealing at different temperatures breaks certain N-H

complexes, may be used to identify hydrogenation type

• Hall measurements will more directly ascertain effects of

centers on carriers

• Thermopower measurements will qualitatively ascertain

degree of doping change due to hydrogenation

• Transport Measurements

• Electrical Characterization - DLTS


Summary

• The hydrogenated samples exhibit lessened effects of

localization centers while retaining substitutional nitrogen

• Further studies will be conducted to verify which N-H

complexes are forming and to analyze their effect on the

band structure and carriers.

Acknowledgements

OCAST OARS 12.2-040

DFT calculations performed at OSCER at the University of Oklahoma

the role of n-h complexes in the control of localized center...

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