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Journal ofC~stalGrowth 12 5 (1992) 373374 o~CRYSTAL

North-Holland GROWTH

Letter to the Editors

ZnSe blue-light-emitting diode

A.N. Krasnov, Yu.N. Purtov, Yu.F. Vaksman and V.V. Serdyuk

Odessa State Unirersity, 270057, Petra Velikoho Str. 2 , Odessa-57, Ukraine

Received2 7 July 1992

A zinc selenide p n junction diode has been formed b y L i thermal diffusion. Blue electroluminescence has been observedfrom

this structurein forwardbias at roomtemperature. The external quantum efficiencyis about 0.5%.

Because of its wide band gap (of around 2.7 Inversion of the conductivity type was per-

eV at room temperature) zinc selenide is a formed in two steps. At first the compensatedpromisingmaterial for opto-electronic device fab- layer, 5 x iO~~cm thick, was produced on the

rication. Recently, considerable efforts havebeen low-resistive substrate by annealingof the crystalspent in attempting to fabricate blue-light-emit- at 1050 K for 20 h in molten Zn towhich 5% (by

ting diodes (LEDs) fromZnSe. The major obsta- weight) of metallic tin was added. Earlier it has

cle to workin thisarea has beenthe difficultyto been shown [31that tin in ZnSe acts as a deepproduce p-type material. It is well known [1,21 compensating acceptor when substituted on a Se

that p n junction formation in ZnSe by thermal site. Then lithium was introduced into the corn-

diffusion of acceptor dopants such as P, As or Au pensated layer by thermal diffusion at 800 K for

is complicated by self-compensation effect, which 20 m m in a vacuumcamera. This was achieved byoccurs in wide band gap compounds. Moreover, preliminary thermal pulverization of high purityalmost all the ZnSe diodes exhibit yellow or or- metallic Li onto the sample. After this procedure,

ange band emission. the sides were mechanically treated and typicalThe purpose of this paper is to report a new diode dimensions were 0.2 X 0.2 X 0.4 cm. A

method to produce p n junction blue-light-emit- schematic construction of this diode is shown in

tingdiode, fig. 1 .In this study, the LED was fabricated by the

formation of a p-type layer on the n-ZnSe. The

base material usedwassingle crystal grown from Blue light emission

thevapour phase. The resistivityofthe as-grown

n-ZnSe was above 1012 (1 cm due to self-corn- Au

pensation duringcrystal growth. Slices parallel to ~ p-ZnSeSnLI

the (111) plane were cut fromthe boule and then low-resistive

annealedat 1100 K for70 h in molten Zn usinga n-ZnSevacuum-sealedquartz ampoule. The resistivity of

such n-ZnSe was of the order 0.1 1 1 cm. After

this treatment, the samples showed bright ultravi-olet photoluminescence (PL) at room tempera-

ture. Fig. 1 . ZnSeblue-light-emitting diode.

0022-0248/92/105.00 1992 Elsevier Science Publishers B.V. All rights reserved

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374 A.N. Krasnoi ci a l. /ZnSeblue-light-emitting diode

A Electroluminescence(EL)appears at forwardbias

arb.f~. ft ~ ~lrn~a~0~

Q8 / exhibits a bright band centred at 2.65 eV (half-/ width about 12 meV) and a series of weak linesin

/ lot the vicinity of2.532.63 eV separated from each

0 .6 1 2 other by equal distances. They correspond to/~ recombinationthrough shallow levels[41.The PL

04 / spectrum of the ZnSe : Sn : Li layer looks similar./ 1 01 Weassume that the radiative recombinationgoes

/ to p-ZnSc.02/ Above 10 5 K, blue-light emission becomes pre-

dominant. The EL spectrumis characterized by asingle hand at 300 K (fig. 2). However, thebright-

2,60 2b5 ril,eV ness of this EL decreases by about an order ofFig. 2. EL spectrum from p n junction (1) andbrightness magnitude under increasingtemperature from 77

current curve(2) measured at300 K. . . . -

to 360 K. The brightness ts approximately linearwith current at a current density of 10 2