The main lines in the photoluminescence spectra of Zn1Cd1-xTe single crystals grown by a modified Bridgman method in the compositional range of 0≤X≤0.25 have been identified. All crystals show only near-band-edge emission. To assist in the identification, various samples with different compositions were annealed under a Cd atmosphere. In the pure crystals, the prominent (A°, X) bound exciton line, as well as the doublet at longer wavelengths, disappear after the annealing. In contrast, the treatments do not change significantly the PL spectra of the mixed crystals

Allred, David D.

Allred, Worth P.

González-Hernández, Jesus

López-Cruz, Elías

Reyes-Mena, A.

BYU ScholarsArchive (Brigham Young University)

Brigham Young University BYU ScholarsArchive Faculty Publications 1990-01-01 Annealing Behavior of the Photoluminescence Lines in CdTe and Znx Cd1-x Te Single Crystals David D. Allred allred@byu.edu A. Reyes-Mena Jesus González-Hernández Elías López-Cruz Worth P. Allred Follow this and additional works at: https://scholarsarchive.byu.edu/facpub  Part of the Astrophysics and Astronomy Commons, and the Physics Commons Original Publication Citation J. González-Hernández, A. Reyes-Mena, D.D. Allred, Elías López-Cruz, and W.P. Allred, "Annealing Behavior of Photoluminescence lines in CdTe and ZnxCd1xTe Single Crystals," in Properties of II VI Semiconductors: Bulk Crystals, Epitaxial Films, Quantum Well Structures, and Dilute Magnetic Systems, Materials Research Society Symposium Proceedings Series, 161, 33-38, (199). [http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8111114&fulltextType=RA&fileId=S1946427436218][http://dx.doi.org/1.1557/PROC-161-33]. BYU ScholarsArchive Citation Allred, David D.; Reyes-Mena, A.; González-Hernández, Jesus; López-Cruz, Elías; and Allred, Worth P., "Annealing Behavior of the Photoluminescence Lines in CdTe and Znx Cd1-x Te Single Crystals" (1990). Faculty Publications. 1191. https://scholarsarchive.byu.edu/facpub/1191 This Peer-Reviewed Article is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Faculty Publications by an authorized administrator of BYU ScholarsArchive. For more information, please contact ellen_amatangelo@byu.edu. ANNEALING BEHAVIOR OF THE PHOTOLUMINESCENCE LINES IN CdTe AND Zn~ Cdl_~ Te SINGLE CRYSTALS J . GONZALEZ-HERNANDEt. A. REYES-MENA*. ELIAS LOPEZ-CRUZ·, 0. 0. ALLRED' AND WORTH P. ALLREO& ·Depllrt~mento de Fisic~ . Centro de Investig~ci6n y de Estudios Av~nlados del IPN . Apdo. Postlll 14-740, 07000 Hhico. O. F. +Dep~rt~mento de Fisicll del Instituto de Cienchs, Universldlld Aut6nomll de Puebh, Apdo . Poshl J - 48, Puebl~ 72570. Pue . Mhico. 'Physics lind Astronomy Oepllrtment, Brigh~m Young University, Provo, UT. &Galtech Semiconductor Haterials Corp. , Ht . Plellsent, UT . ABSTRACT The main lines in the photoluminescence spectra of ZnlCdl_~Te single crystals grown by II modified Brid<}'llan method in the cOGlpositlonal r~nge of Og~0. 25 have been identHied. All crystals show only near-band-edge emission. To IIssist in the identifintion , vllrious ulllples with different CQIIIPositions were annealed under II Cd IItmosphere . In the pure crystals, He pr_lnent (A",X) bound exciton line . as well lIS the doublet at longer wavelengths , disappear after the annell11ng . In contrut . the treet..ents do not change significantly the Pl spectra of the mixed crystals . INTI!QOUCTION large ern c<lIdllium telluride (CdTe) and zinc no-iull telluride (Zn Cd 1_X Te) single crystal substrates hllve fllllny potenthl IIpplications iA the fabrication of electroniC and optoelectronic devices II]. Interest in this wide-gap ~teri."l has also developed due to its chemical compatibi-lity and close lattice match to the I.portant infrared detector material HgCdTe . HO'olever , the understanding of the native defects and their complex 'oIith residual impurities is important in order to have a better contr ol of both their optical <lind electric."l properties . In the last fe'ol years numerous studies on the photoluminescent (PL) properties of CdTe cryshls have been reported 12-5) and only few on ZnxCd1_xTe (5-8] . In the present paper we r eport on the PL f r om lIS-prepared and Cd vapor ~nnealed Zn)(Cdl_~Te (OSX~. 2S) single cr ystals , For .,,11 the inves-tigated values of x, the prominent emission lines occur In the e~citon region indicating", high cryshlline qu""l1ty. In pure CdTe cr ystals , the 15K PL spectr "" uhibit t'olO m",in lines In this region at 778. 2 nm (1.S934eV) and 779. 5 nm (1 . 5907eV) . The fo~r line occurs in the energy range where recombinlltion of excitons bound to sh""llow neutral donors (O·,X) has been reported [g) . Our studies on ""nnul.d CdTe S4mples under Cd atlllosphere indicate thllt the 1. 5907 eV line is related with recombina-tion of excitons bound to cad .. iUII vllCllncies [51 . We also obseryed that in the IIlhed cryshls exciton rec_bination """inly occur s yh neutral donor shtes . EXPERIMENTAL All samples were grown fro. the llelt by a "'Odified Brid~n .-ethod at G""ltech Se-lconductor M."terlllls COrporllUon . The composition of the ZnxCdl_xTe samples was determined frOll electron .icroprobe analysis <lind frOll! the energy of the uin uciton line observed in the 15K Pl spectra [6). All as-prepared crystals were unintentionally doped and have lin appro-'hI. A ••. Soc. Symp. "roc. Vol. 181 .• , ttO MII.rI.,. A .... fell Society ximate room-temperature resistivity of 5ll0 ' and 8ll0' n cm fo r the mhed and pure crysttlls , respectively. All spectr a in the as~prepared samples "'ere taken on (1l0) cleaved surhces at 15K . The hser po",er , from an argon ion laser , impinging on the sample ",as of 0. 5 mW ",ith the laser beam focused using cylindrical optics . The Pl emission ",as spectrally analyzed ",ith a double monochromator , ",ith slits set to achieve a resolu-tion of less than lAo Annealing "'as ca r ried out in a sealed Quartz ampoule under Cd satura-ted isothermal conditions at 600·C for t"'o hour s . Before the Pl ",as measu-red all annealed sampl es "'er e chemica l ly etched to remove the sur face damage. The chemical treatment ",as as follo",s : ifmlersion in a 1% bromine in ITI!!thanol solution for 30 seconds follo",ed by a 60 seconds ifmlersion in a solution of 3. 5M KOH in 1 liter of H20. RESULTS AND DISCUSSION figure shows typical 15K Pl spectra for three as-pr epared ZnxCd I-X Te cleaved surfaces with x .. O, 0. 10 and 0. 25. All three spectr a ar e plotted ",ith the same abscissa . Consider ing the origin of the emission lines . the Pl spectra in the f igure can be divided into three regions : a) the exciton region , for wavelengths near t he band-gap: bl the free to bound (f-A) and bound to bound (O-A) transitions , for intermediate ~ ' s and, c) emission at lonler :I. ' s associated with crysttll imper fections and deeper impurity levels 6. 10] . This lat t er emission generally appea r s in the Pl spectra as a broad band at approximat ely 50 to 100 nm above the exciton lines . Notice that none of the three spectra in fig . 1 sho"'s any significant emiSsion in this latter region , which is an indication of high crystalline Quality. The identification of the emiss i on lines in the intermediat e r egion , as due to electron-accept or and donor-acceptor t r ansitions has been re-ported in a previous study [11] . In the exciton region. f ree exciton recombin5 t ion results in the emission of photons ",ith an energy 10 . 5 meV less t he,n the band gap , ",hich , at 15K is at 772 nm ( 1.606 eV) , 743 . 5 nm (1.668 eV) and 695 . 9 nm ( 1. 78lgeV) for x .. O, 0. 10 and 0. 25 , respectively. This line is denoted by (X)n .. l in the figure . The exis t ence of several different donors and acceptors in CdTe has al r eady been pOinted out [12] . free excitons can get trapped by the potential of the impurities becoming bound excHons . The two main lines in the exciton region of our pure CdTe crystals at 778. 2 nm (1.5934 eV) and at 779.5 nm (1.5907 eV) hftve been identified ftS due to the recombination of excitons bound to shallow neutral donors {DO . X) [9] ftnd to neutral acceptor (AO , X) states . respectively. The identification of the 1. 5907 eV line as due to a (A" , X) process is based on the changes observed in the Pl spectra induced by the anneal-ing under Cd atmospher e . which are sho",n in Fig . 2. The complete Pl spec-tra as well as the resol~ed exciton regions ar e sho",n f or as-pr epared (a) and for annealed (b) samp l es . As can be seen . two drastic changes occur upon annealing : one is that the lines in the range of 790-800 nm denoted by (F-A) and (D-A) have been drastically r educed and the other is the disappearance of the (A" . X) line . The broader bands found at 790-800nm are generally accepted to involve deep acceptorll~e le~els associated with a comple~ cented3]. and more recently t hei r origin has been related with cadmium vacancies [13]. In a recent publication Seto et al [5]have seen that , under similar annealing conditions , the intensity of a bound e~citon 10:_1 / ~ WAVELENGTH )IM;L[ ~m'IS 1 •• to •. • t. ". ,. Flg, 1. Photoluminescence spectra of Zn~Cd\_~Te single crystals wlth x-o. 0.10 and 0.25. Details on the assig-ments and identification of various lines can be found in the text . line at 1. 5896 eV in their 4. 2K PL spectra of high quality p-type CdTe is drastically reduced after the annealing ; their results strongly suggest that this line can be ascribed to the recombination of excitons trapped at Cd vacancies . Our results in annealed CdTe crystals under a Cd atmos-phere provide further evidence for the previously proposed assignments for the PL bands in the region of 790-800 nm as well as for the origin of the (A· ,X) line at 1. 5907 eV. The identification of the 1. 5907 eV line is also consistent with its temperature dependence because the PL intensity of acceptor- bound excitons decreases very rapidly with increasing tempe-rature [11] . Figure 3 shows the PL sp'!ctra of an as-prepared (a) and Cd vapor annealed (b) ZnxCd\_x Te with x,,0.09. Similar to the pure CdTe crystals . the Pl spectra of the as-prepared mixed crystals show a dominant near-band-edge emission. In the exciton region the line at 753.2 nm (1.6463eV) has the same exciton binding energy of 2 meV as the line labeled with (O",X) in the PL spectra of pure CdTe . lending evidence that this fea-ture is due to the same transition in both cases. The line at 756 nm (1.6402 eV) has been identified with a (A·,X) transition based on a va-riety of evidence. In the first place . the exciton binding energy of 7. 5 meV is close to the calculated binding energy of excitons bound to accep-tors of 7 meV [14J . In the second place, this line is thermally quenched at temperatures exceeding SDK. This assignment is also in agreement with previous observations in other alloyed compound semiconductors showing that the (Ao.X) lines are much more sensitive to alloying and that the linewidth increases at a rate much greater than that of the (O. X) levels (15). We have observed that in the exciton region . the Pl spectra of the mixed crystals look very similar regardless of x in the range investigated , tals The result of the annealing under Cd atmosphere for ZnXCd\_X Te crys-is quite different than that observed in the pure crystals , In the " CdT. • I ..... , .,; • ,v," !i 6 !k I~ (, .. , (0-'1 '1 1\ ,. '" ~ IL-~I~ ( •• ' QIA.-","""tO blCd -.opor ~ .-I • J ~ ". ~ •• ~ W4VElENGTH (nm) fig. 2. Photoluminescence spectr~ of ft CdTe single crysbl . before ( ... ) Md after (b) anneaUng at 600C/2hrs. in a salur 4ted Cd vapor atmosphere . The insert shows the resolved exciton region , • • • 11l'," C z.., CA", r. X·Q.09 ,'As -Ii'"""," D)Cd_~ I ")'j'\"(/t"" V ~HLO m •• WI'o'tlEHGTH (11m) .ro Fig . 3. Photoluminescence spectra of as-prepared (a) and Cd vapor annealed (b) Z"xCdl _xTe single crystals with x.O, 09 . " mixed crystal II small dec r ease in the amplitude of the (AO , X) line and II change in the shape of the br oader e<nission line located at about 20-30 n. above the uciton range are observed . Before anneaHng the well defined doublet labeled 45 (F-A) and (D-A) becomes II single line with II posltlOtl 4t 769. 5 n .. (1.6114 eV) in between the (F-A) and (D-A) doublet. rrOli the dependence on temperature and e~cit4tion intensity we haye identified this line with I (D-A) transition . We 1!lIVe aho obsel"ved that 6S II result of Cd annuling II neli broad emission band appea r s at about 795 n. (1.5597 eV) probably origina ted at deeper defect levels created during the thermal annealing . however , fu rther studies are needed in order to have a betler understanding about the origin of this band. Based on the annealing behavior of the Pl spectra of CdTe and Zn it Cd I-it Ie crystals. one can conclude that. in contrast to pure CdTe. the fre~ to bound . the bound to bound and the (Ao . X) bands in the mhed crys-tals are probably not related with recombination involving cadmium vacancy levels. These results provides further support for the observation that In addition to CdTe impr oves crystal quality [16. 171 . particularly reducing the density of group II (Cd or Zn) vacancies . CONCLUSIONS The photoluminescent properties of ZnilCd -xTe single crystals for 09 'ill. 25 have been studied . To assist in the i~entHlcation of the lines in the spectra . as-prepared and annealed (under Cd atmosphere) ullples were Measured . In all crystals . the d_inant e.isslon occurs at the near-band-edge region. indicating good crystalline quality. In the pure crys-tal . the two main eilciton lines are identtfied with recombination of excitons at neutral shallow donors (778 . 2 nm) and at neutral donors (779. 5 nm). The assignment of the latter line was deduced from its anneal-ing behavior under a saturated Cd atmosphere . We also observed that the doublet in the wavelength range of 790-800 rom disappears after the anneal-ing. which indicates that the levels involved in that transition are aho related to cad.Ium vacancies . In the as-prepared mixed crystals, we observed that the Pl spectra is qualitatively sillilar r egardleu of the values of il . By an",logy with the pure crystal . the main eilciton line is identified .. ith '" (D° , X) tranSi-tion and a weak (A" .X ) line is also observed . From the observed changes in the PL spectra of Cd annealed mixed crystals . we concluded that the -.,in lines In the spectra are not related with transitions involving Cd vacancies. REFERENCES K. Zanio. and A.C. In Semiconductors and Semimetals, Beer (Academic . N. Y. 1978) . Vol . n. edited R, K. Wil1ardson 2. J . L.Pautrat. J.H.F rancou , N,Hagnea . E.Molva and K. Saminadayar. J . of Cryst . Growth. 72, 194(1985). 3, N. C.Giles-Taylor. R. N.Blcknell. O. K. Bhnks. T. H. Myers and J . F.Schetli-na , J. Vac. Sci . Technol . A3.76(1985). 4. J . P. laurenti. G.Sastide . H. Rouleyre and R. Trlboulet. Sol . State Coora •• 67 , 1127(1988). " 5. S. Seto. A. Tanaka. V. Masil . S. Oairaku and M.Ka .. ashima , Appl . Phys . lett . • 53.1524(1989). 6, D.J.Olego. J . P. Faurie. S. Sivanalh.sn and P.M.Raccah , Appl. Phys, Lett . , !l.1172(1985). 7. E.eollen. R. A. Street lind A. Muranevich. Phys. Rev. 828. 7115(1983), B. J.H.Dinan and S.B.Qadri , J . Vac . Sci. Technol. Al.851(1985). 9. J.l.Pautrat , J .M. Francou. ~ . Magnea . [,Molva and K.Saminadayar. J . of Cryst. Growth, 72,194(1985), 10. V.N . Babentsov, S. I . Gorban, LA. Salkov and N. I.Torbaev , Soy. Phys. Semicond •• Kl. 1043(1987) . 11 . J . Gondlez-Hernindez . Ll6pez-Cruz , D.O. Allred and W. P. Allred. sub-mitted to J . of Vac. Sci . and Technol . (1989>' 12. P, A.Sirrrnonds, R.A.Stradling. J . R. Birch and C.C.Bradley, Phys, Shtus Solidi (b) 64,195(1974). 13, J,M, Figueroa , F.Sanchez-Sinencio, J . G. Mendoza-Alvarez. O.Zelaya . C. Vazquez-Lopez and J . S.Helman. J . Appl. Phys. 60. 452(1986). 14 . R. E.Halsted and M.Aven , Phys. Rev. Lett .. ~. 64(1965). 15. C. Mikkelsen and J . B.Boyce, Phys. Rev. Lett .. 49. 1412(1982). 16 . S.L.Bell and S.Sen . J. Vac. Sci. Technol " Al.112(1985), 17 . A.Sher . A.8.Chen , W. E.Spicer and C. K.Shih. J. Vac . Sci. Technol .. Al,105(1985). 

Annealing Behavior of the Photoluminescence Lines in CdTe and Znx Cd1-x Te Single Crystals

https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=2190&context=facpub

Annealing Behavior of the Photoluminescence Lines in CdTe and Znx Cd1-x Te Single Crystals

Abstract

Similar works

Full text

Available Versions

BYU ScholarsArchive (Brigham Young University)