Solid State Communications, Vol. 28, pp. 835-836. 0038-1098/78/1201-0835 $02.00/0 © Pergamon Press Ltd. 1978. Printed in Great Britain.

ELECTROLUMINESCENCE OF ERBIUM-IMPLANTED ZINC SULPHIDE DIODES

C.C. Yu* and F.J. Bryant

Department of Physics, University of Hull, Hull, England

(Received 17 July 1978 by C W. McCombie)

Erbium ions have been implanted into zinc sulphide single crystals which were then each provided with one rectifying contact and one ohmic con- tact. Bright green d.c. electroluminescence is produced in the ZnS : Er diodes when they are operated in reverse bias. The emission is character- istic of Er a* ions.

ELECTROLUMINESCENCE of rare earth doped zinc sulphide films and powders has been reported previously [1 -3 ] . Light emission has also been observed from zinc sulphide diodes when forward biased [4] or when re- verse or forward biased [5]. However, no electrolumi- nescence from zinc sulphide diodes doped or implanted with rare earth ions has yet been reported.

In the present work, boules of zinc sulphide were grown by a Bridgrnan method under an argon gas press- ure o f ~ 7 × 106 Pa. From these boules single crystal chips were cleaved and fired for 200 hr at IO00°C in molten zinc containing 5% aluminium. This treatment reduced the bulk resistivity of the zinc sulphide to 102-103 ~-cm.

Samples were implanted with l~6Er in the first charged state. An implantation fluence of 1 x 10 is ions cm-2 at an ion flux of 0.2/aA cm-2 and an ion beam energy of 25 keV was used. The implantations were carried out with the samples at 77 K.

In order to make ohmic contacts to the zinc sul- phide, freshly cleaved surfaces were wetted first with a mixture of 50% indium and 50% gallium and then more indium was added. After firing in a nitrogen atmos- phere for 3 min at 385°C ohmic contacts were formed. Their ohmicity was proved by the observation of the linearity of the current-voltage characteristics of zinc sulphide dice, each with two indium contacts.

In order to produce a light emitting zinc sulphide diode one ohmic contact was made on the face opposite the implanted surface and then gold was evaporated on to the implanted surface to provide the rectifying con- tact. No post-implantation annealing was necessary to obtain electroluminescence. Uniform bright green emission was readily observed at room temperature

* Permanent address: Kirin Institute of Physics, Changchun, China.

20

.¢C

E 12(Fo ar ) L

l

f

. l - / j t

/,, V0 / .... ./" ~ / / ' ,

10 15 20 Voltage /V

I, (Reverse)

25 30

. t~

" x

oA

o 4--

e,

Fig. 1. Current-voltage and luminance-voltage charac- teristic of erbium-implanted zinc sulphide at room tem- perature; . . . . . . . , forward bias (I1); . . . . , reverse bias (12); , electroluminescence emission in- tensity in reverse bias (L).

from the implanted layer under the gold contacts when a reverse bias was applied (i.e. with the indium contact positive).

For a typical diode the current-voltage and lumi- nance-voltage characteristics are shown in Fig. 1. It was found that for each diode the turning voltage for electroluminescence, VD, depended on the erbium ion beam energy used during implantation. The higher the implantation energy then the greater was VD. This feature allows the possibility of manufacturing diodes with a selected turning voltage for emission.

835

836 ELECTROLUMINESCENCE OF ERBIUM-IMPLANTED ZINC SULPHIDE DIODES Vol. 28, No. 9

Wovenumber /era -~ 25000 2250~, 19000 18000 17000 16000

4G,V'2~41)s/2 4S3 ~ --* 4 I,s/2 2H ~2"* 41,5/2

A*,o, Ax,o , s 6 o ' 660

Wavetength /nm.

15000

4E 41 9/2 ~ s/

6t,0 680

Fig. 2. Electroluminescence emission spectrum of an erbium-implanted zinc sulphide diode in reverse bias at room temperature.

The electroluminescence spectrum of a typical diode is shown in Fig. 2. The emission lines occur at 386.2,412.2,532.8,552.8 and 664.8 nm corresponding respectively to transitions from 4G, u2, 2H9/2, 2H, u2, 4S3/2 and 4F9/2 to the ground level 4I, s/2 of Er 3÷. Most of the emission energy is concentrated in the 530 nm line.

The energy efficiency was estimated to be ~ 2 x 10 -6 . This figure could probably be improved by optimising the implantation and annealing parameters but this work illustrates the values of implantation as a technique in producing light emitting diodes.

REFERENCES

1. CHASE E.W., HEPPLEWHITE R.T., KRUPKA D.C. & KAHNG D., J. Appl. Phys. 40, 2512 (1969).

2. BROWNM.R.,COXA.F.J. ,SHANDW.A.&WlLLIAMSJ.M.,SolidStateCommun. 9, 1 (1971).

3. WAITEM.S.& VECHT A.,AppI. Phys. Lett. 19,471(1971).

4. KUKIMOTO H. & ODA S., J. Luminesc. 12/13,923 (1976).

5. OZSAN M.E. & WOODS J., J. Phys. D. (Appl. Phys.] 10, 1335 (1977).