Temperature Dependence of the Band-Edge Injection Electroluminescence of 3C-SiC pn Structure

A.M. Strel’chuka, А.А. Lebedevb, N.S. Savkina, and A.N. Kuznetsov

A.F.Ioffe Physico-Tekhnical Institute Russian Academy of Science, Politekhnicheskaya 26, St. Petersburg 194021, Russia

e-mail: aanatoly.strelchuk@mail.ioffe.ru, bshura.lebe@ioffe.mail.ru

Keywords: 3C-SiC, pn Structure, Sublimation heteroepitaxy, Band-edge electroluminescence.

Abstract. We present the injection electroluminescence spectra in the temperature range 290-760 K

of 3C-SiC pn structure, which was fabricated by sublimation epitaxy in vacuum on 6H-SiC

substrate. The dominant emission band of injection electroluminescence (IEL) spectrum was

observed in the green region; at room temperature the IEL intensity outside the region of hν ≈ 2.0-

2.5 eV was less than 3% of that of the green peak. The peak parameters at room temperature are:

hνmax ≈ 2.32 eV, full width at half maximum w ≈ 100 meV. The green peak shifted in the long-

wave direction with increasing temperature; the hνmax (T) dependence was linear with the slope of -

1.3x10-4 eV/K. Both the IEL intensity of the green peak at hνmax and band width w increased upon

heating. The w(T) dependence was linear with the slope of 4.6x10-4 eV/K; intensity increased with

the activation energy of 70 meV. The green IEL band can be considered to be due to the free

exciton annihilation or to the band-band recombination and edge IEL increasing with rising

temperature can be explained by the nonequilibrium charge carriers lifetime increasing.

Introduction

Band-edge injection electroluminescence (IEL) of pn structures based on different SiC polytypes is

not usually a dominant one. Often, it is even hard to detect. Presence of noticeable band-edge IEL

manifests high quality of the pn junction and indicates low level of defects and impurities, which

usually act as rival recombination centers. In low-dimensional structures the parameters of the

band-edge IEL give important information about quality and parameters of the structure.

Fabrication of the heterostructures using different SiC polytypes attracts significant attention to the

3C-SiC polytype, which has the narrowest bandgap. Even though some features of band-edge IEL

in 3C-SiC pn structures are already determined [1,2], nevertheless the properties of this band and

their interpretation are still debatable. Moreover, some basic parameters of 3C-SiC also are

debatable (for example, the value of a linear variation of the energy gap varies from -5.8x10-4 eV/K

[3] to - 3.3x 10-4 eV/K [4] at high temperatures and value of exciton binding energy varies from

13.5 meV [5] to 27 meV [6]).

Earlier we reported the current-voltage characteristics and current dependence of the intensity of

IEL in high-quality 3C-SiC pn structures, which were fabricated by sublimation epitaxy (SE) on

6H-SiC substrate [7]. The aim of the present study is to investigate the temperature dependence of

the band-edge IEL of high-quality 3C-SiC pn structure with most intensive and uniform green IEL.

Experimental results and discussion

The pn structures were fabricated by SE in vacuum on 6H-SiC (0001) substrate produced by Lely

method. In the initial stage of epitaxial growth on the 6H SiC substrate, a buffer n-6H SiC layer of

thickness ~1.5 µm was formed; then a polytype transformation and growth of an n-3C-SiC epilayer

took place (4.5 µm thick, Nd-Na∼2x1017 cm

-3, hole diffusion length is about ~1.5 µm) [7]. The pn

junction was formed by SE growth of a p+(Al) - 3C-SiC epilayer (Fig. 1).

Materials Science Forum Vols. 556-557 (2007) pp 427-430Online available since 2007/Sep/15 at www.scientific.net© (2007) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/MSF.556-557.427

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 129.187.254.46, Technische Universitaet Muenchen , Muenchen-12/11/14,00:18:03)

An ohmic contact to the p-type region was formed by deposition of Al and Ti layers followed

by their annealing in vacuum at 1100oC. Mesa structures of 10

-4 cm

2 area were fabricated by

reactive ion-plasma etching to a depth of about 3 µm.

Small-area diodes characterized by a uniform green IEL over the diode area were selected. The

results of an investigation of IEL spectra at room temperature and in the temperature range 290-

760 K are presented in Fig. 2 and Fig. 3. The emission band in the green region is a dominant

feature of the spectrum; at room temperature (RT) the IEL intensity outside the region of hν ≈ 2.0-

2.5 eV is less than 3% of that of the green peak. The peak parameters at RT are: hνmax ≈ 2.32 eV,

full width at half maximum (w) is about 100 meV; the red part of the spectrum has kink at hν ≈

2.15-2.25 eV.

On heating the pn structure the peak of green IEL is shifted in the long-wave direction; the

hνmax (T) dependence is linear with slope of about -1.3x10-4 eV/K (Fig. 4a). Both the IEL intensity

of the green peak at hνmax and band width w increases on heating. The w(T) dependence is linear

with slope of about 4.6x10-4 eV/K (Fig. 5a) and intensity is increases with activation energy of

about 70 meV (Fig. 5b).

The small width of the green peak and observed earlier [7] super linear dependence of the IEL

intensity versus current, emission enhancement with rising temperature are distinctions of the IEL

observed from the so-called “defect” emission in 6H-SiC at a close energy of the intensity

maximum. The defect IEL band in 6H-SiC pn structures is much wider (curve 2 in Fig. 2), saturated

with current increasing [8] and quenched with rising temperature above room temperature [9]. The

1.6 2 2.4 2.8 3.2

Photon energy [eV]

0

0.2

0.4

0.6

0.8

1

EL intensity L [arb.un.]

2

1

Fig. 2. Room temperature injection

electroluminescence spectra of 3C-SiC

pn structure created by SE (curve 1,

current 10mA, S=10-4 cm

2) and 6H-

SiC pn structure created by ion

implantation of Al (curve 2, current

2mA, S = 7×10-4 cm

2).

Fig. 1. Coordinate dependencies of

secondary electrons (curve 1) and

electron beam induced current

(curve 2) signals obtained in

scanning of the cross-sectional

surface of diode ([7]).

0 2 4 6 8 10 120,0

0,2

0,4

0,6

0,8

1,0 Current, arb.un.

6H-SiC (Lely)

(n+)

6H-SiC

(n)3C-SiC

(n)3C-SiC

(p+)

2

1

x, µµµµm

X [microns]

Current [arb.un.]

428 Silicon Carbide and Related Materials 2006

1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7

0

100

200

300

400

500EL intensity [arb.un.]

Photon energy [eV]

T, K

289K

337K

392K

441K

497K

557K

605K

654K

704K

764K

Fig. 3. Spectra at various temperatures of the band-edge injection electro-luminescence of a 3C-

SiC pn structure grown by sublimation epitaxy on a 6H-SiC substrate at a forward current 5 mA

(50 A/cm2).

green (band-edge for 3C-SiC) IEL band is usually considered to be due to the free exciton

annihilation [1]. In our case difference between Egx and hνmax is roughly proportional to (-2kT)

(Fig. 4b) that is characteristic feature for band-band recombination, however we should point out an

ambiguity in the data on Egx in the region of the linear dependence of Egx on the temperature. The

similar edge IEL increasing with rising temperature was observed earlier in 6H- and 4H-SiC pn

structures [8] and explained by the charge carriers lifetime increasing.

200 300 400 500 600 700 800

2.24

2.25

2.26

2.27

2.28

2.29

2.30

2.31

2.32

2.33

hνmax [eV]

Temperature [K]

200 300 400 500 600 700 800

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Egx-hνmax [eV]

Temperature [K]

Fig. 4. Temperature dependence of the a) peak position hνmax and b) difference between Egx

according to [4] and hνmax.

a b

Materials Science Forum Vols. 556-557 429

300 400 500 600 700 800

0.10

0.15

0.20

0.25

0.30

w [eV]

Temperature [K]

0.0010 0.0015 0.0020 0.0025 0.0030 0.0035

10

20

40

60

80

200

F [arb.un.]

1/T [1/K]

Fig. 5. Temperature dependence of the a) full width at half maximum (w) and b) intensity F of

the electroluminescence calculated as the area under the band-edge peak.

Summary

The injection electroluminescence characteristics in the temperature range 290-760 K of 3C-SiC pn

structure, which was fabricated by sublimation epitaxy in vacuum on 6H-SiC substrate are

presented. The dominant emission band of injection electroluminescence (IEL) spectrum was

observed in the green region (band-edge for 3C-SiC). The peak parameters at room temperature are:

hνmax ≈ 2.32 eV, full width at half maximum w ≈ 100 meV. The green peak shifted in the long-

wave direction with increasing temperature; the hνmax (T) dependence was linear with the slope of -

1.3x10-4 eV/K. Both the IEL intensity of the green peak at hνmax and band width w increased upon

heating. The w(T) dependence was linear with the slope of 4.6x10-4 eV/K; intensity increased with

the activation energy of 70 meV. The green IEL band can be considered to be due to the free

exciton annihilation or to the band-band recombination and edge IEL increasing with rising

temperature can be explained by the nonequilibrium charge carriers lifetime increasing.

Acknowledgement This work was supported in part by the RFBR (grant N 04-02-16632a).

References

1. Yu.M.Altaiskii et al.: Sov.Phys.Semicond. Vol. 13 (1979), p. 1152.

2. M.Ikeda et al.: J.Appl.Phys. Vol. 50 (1979), p. 8215.

3. R.Dalven: J.Phys.Chem.Solids Vol. 26 (1965), p. 439.

4. W.J.Choyke: Mat.Res.Bull. Vol. 4 (1969), p. S141.

5. D.S.Nedzvetskii et al.: Sov.Phys.Semicond. Vol. 2 (1969), p. 914.

6. R.G.Humphreys et al.: J.Phys.Soc.Jpn.Vol. 49 Suppl.A (1980), p. 519.

7. A.M.Strel’chuk et al.: Mater. Science Forum Vol. 457-460 (2004), p. 1057.

8. M.M.Anikin et al.: Semiconductors Vol. 28 (1994), p. 171.

9. M.M.Anikin et al. in: Semiconductor interfaces and microstructures, edited by Z.C.Feng, World

Scientific, Singapore, New Jersey, London, Hong Kong, p.280-311 (1992).

a b

430 Silicon Carbide and Related Materials 2006

Silicon Carbide and Related Materials 2006 10.4028/www.scientific.net/MSF.556-557 Temperature Dependence of the Band-Edge Injection Electroluminescence of 3C-SiC pn Structure 10.4028/www.scientific.net/MSF.556-557.427

DOI References

[8] M.M.Anikin et al.: Semiconductors Vol. 28 (1994), p. 171.

doi:10.1097/00006454-199405000-00031