Effect of Sb on the Prope

GaInP Top Cells

J.M. Olson, W.E. McMahon, and Sarah 

•Background

–Efficiency of GaInP/GaAs tandem 

effect of top cell band gap

–Why Sb?

•Result

–Properties of Sb:GaInP–Sb:GaInP top cells–Sb:GaInP/GaAs tandem cells

•Summary

NREL/PR-520-39859Presented at the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WC

in Waikoloa, Hawaii.
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A Bit of History

• In 1984 - invention of GaInP/GaAs

tandem cell. (Olson)

• In 1989 - 27.3% (Olson et al.)• In 1993 - 29.5% (Bertness et al.)• In 1996 - production of first 

commercial GaInP/GaAs cell (Spectrolab, et al.)

– Space applications, Mars rovers– Terrestrial concentrator applications

• In 1997 - 30.3% AM1.5G 

(Takamoto et al.)

npnp
GaInP/GaAs tandem 

• Ideal top cell band gap for a 

GaAs bottom cell is ~1.9eV (~2eV AM0).

• Typical band gap of GaInP is 

~1.8eV which reduces the ultimate efficiency by about 1 point.

npnp
Ordering in GaInP

• Band gap shift 

– caused by CuPt ordering of 

Ga and In on the Group III sublattice.

• Order parameter and band 

gap energy varies with 

– growth temperature– growth rate, – PH

3 partial pressure, 

– substrate orientation– Type and concentration of 

shallow dopants. 

(Kurtz el al. JEM 1994)

1.881.871.861.851.841.831.82

Band gap [eV]

620 640 6

Gro

Ga 
Effect of Sb on the Bandgap 

• Addition of Sb (TESb) 

during growth can hinder the ordering process and increase the band gap*

• Effect controlled by ratio 

of TESb to PH

3 (Sb/P)

• Effect is largest for 

– B-miscut substrates– Tg ~ 625 ̊C

*Shurtleff et al. APL (1999)

1.881.861.841.821.80

Band gap energy [ev]

0 10 
Sb incorporation vs 

• Under conditions used for top cell, CSb = ~• Activation energy ~4eV, comparable to tha

68

1017

2468

1018

2

Sb concentration [cm-3]

1.14x10-3 1.10 1.12

1/T [K]

644ÞC 620 597

PB880

Sb/P = 25 ppmE

A=4 eV
Surface Concentration 

ΘSb on 

• The 1/e decay length L=23nm• Surface segregation coefficient R = exp(-a

0/L) = 

• Sb surface concentration 

θSb

∝

CSb/(1-R),

θSb = 

• Implies (001) terrace not occupied with Sb-Sb d• Theoretical work - preferred Sb attachment at B

PRL 2005)

10151016101710181019

CSb in GaInP [atoms/cm3]

2.8 3.0 3.2 3.4 

De

pth [μ

m]

Sb/P=0 33 ppm 0 ppm 

V/III=225Rg=4μm/hrTg=625

ū

C

6

ū

B
Ordered domain struc

• Tilted domain boundaries result from ste

et al PRB 51 p9707)

0.25 μm

Sb/P = 6 ppm Sb/P = 12 ppm Sb

1/2113DF
Surface morphologies of Sb:Ga

singular GaAs(100)

Sb/P = 34 ppm 

• For intermediate Sb, surface composed 

of asymmetric hillocks, 5 to 7nm high, 

bounded by low angle B-type facets, Friedman et al APL (1993).

• For higher Sb, s

terraces separa

• This implies tha

type steps on G
Effect of Sb on Se incorp

• Sb, P and Se compete for group V lattice • CSe ∝ α

FSe/(1+

α

FSe

+

β

FSb

+

γ

F

P

)

1000

900800700600

Sheet resistance [ohms/ 500]

0 10 20 30 40 50

Sb/P [ppm]
Effect of Sb on Group I

Occupations

Mechanism?

789

1017

2

Hole concentration [cm-3]

0 10 20 30 40 50

Sb/P [ppm]

0.530.520.510.50

Ga concentration x in GaxIn1-xP

0

5 

6ÞA

15ÞA
Sb-doped GaInP top c

• The base/emitter/window thicknesses are 2μm, 0.

respectively

• The base p varies from 7e16 to ~2e17 cm-3• The emitter sheet resistance varies from 500 to 10

-14-12-10

-8-6-4-2

0

J [mA/cm2

]

0.0 0.5 1.0 1.5

Voltage [V]

Sb/P [ppm]

02550

1.00.80.60.40.20.0

Internal QE

2.0 

Pho

S
Top cell device parameter

• Internal Jsc decreases with E

g slower th

• Voc increases more slowly than E

g.

1.881.861.841.821.80

Band gap energy [ev]

0 10 20 

Sb

17.517.016.516.015.515.014.5

 Jsc [mAcm-2]

1.80 1.82 1.84 1.86 1.88

Band gap energy [eV]

 Theoretical Jsc Internal Jsc
Sb-doped GaInP/Ga

tandem cells

• T

TotJsc Voc 

Ff = Eff 

-16-14-12-10

-8-6-4-2

0

Current mA/cm2

0.0 0.5 1.0 1.5 2.0 2.5

Voltage (V)

Active Area, AM1.5GOne Sun estimated IVs

 Tandem Top Bottom

pc327n5_CJtop=14.81(1.46)Jbot=14.91(1.02)For TandemJ=14.838V=2.4806FF=87.884 %Eff.=32.348 %
Summary

• Sb can be used to increase Voc o

top cell.

• The photovoltaic quality of GaInP 

unaffected by the presence of Sb

• Sb-doped GaInP/GaAs tandem c

promise for achieving efficiencies 
Acknowledgement

• Andrew Norman• Jiang Chun-Sheng• Michelle Young• Alan Kibbler• Bob Reedy• Tom Moriarty