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RESPECTIVE ROLES OF IMPURITIES AND DEFECTS IN Al/Ga INTERDIFFUSION IN ION IMPLANTED GaAs-AlxGa1-xAs SUPERLATTICES
E. Rao, F. Brillouet, P. Ossart, Y. Gao, J. Sapriel, P. Krauz
To cite this version:
E. Rao, F. Brillouet, P. Ossart, Y. Gao, J. Sapriel, et al.. RESPECTIVE ROLES OF IMPURITIES AND DEFECTS IN Al/Ga INTERDIFFUSION IN ION IMPLANTED GaAs- AlxGa1-xAs SUPERLATTICES. Journal de Physique Colloques, 1987, 48 (C5), pp.C5-113-C5-116.
�10.1051/jphyscol:1987520�. �jpa-00226724�
JOURNAL DE PHYSIQUE
Colloque C5, suppl6ment au noll, Tome 48, novembre 1987
RESPECTIVE ROLES OF IMPURITIES AND DEFECTS IN Al/Ga INTERDIFFUSION IN ION IMPLANTED GaAs-AlxGa,-,As SUPERLATTICES
E.V.K. RAO, F. BRILLOUET, P. OSSART, Y. GAO, J. SAPRIEL and P. KRAUZ
Centre National d l E t u d e s des Telecommunications, Laboratoire de BagneUX, 196, Avenue Henri Ravera, F-92220 Bagneux, France
L'influence des d6fauts d'ivolantation, S 6 o a r 6 ~ des effets associ6s aux charoes des ivouretds, a 6t6 6tudi6e sur l'interdiffusion dtA1/Ga dans des sunerr6seaux ( S Q ) CaAs-Al0.3Ga0.7As. L'imolantation des 616ments iso6lectronioues 31~' et 2 7 ~ 1 + ont 6tC effectubs dans des SR 1 deux temp6ratures (25OC et 250°C) dans le but d'obtenir diff6rente.s densit6s de d6fauts Dour chaaue 616ment. Les uronri6t6s de ces structu- res, avant et aprss recuits 1 850°C durant 6 h, ont 6t6 6valu6es 1 l'aide de nlu- sieurs technioues d'analyses. Ainsi, nous avons mis en 6vidence la d6nendance d'in- terdiffusion sur la densit6 des d6fauts et la dur6e de leur recuit.
ABSTRACT
The influence of imolant damaee, seoerated from imourity chanve associated ef- fects, has been investi~ated on Al/Ga interdiffusion. I m ~ l a n t s of electrically inac- tive isoelectronic elements 31~' and 27~1' were oerfomed in molecular beam eoitaxy grown (MBE) R ~ A S - A L ~ . ~ C ~ ~ . ~ A S sunerlattices (SLs'l at two distinct temperatures (25OC and 250°C) to generate different damape densities. Their orooerties, before and af- ter anneals at 850°C for ~ e r i o d s uo to 6 h, were evaluated using several characteri- zation techniques. An unambiguous evidence to the implant damage and anneal duration dependent Al/Ca interdiffusion is presented and discussed.
Since the demonstration ( 1 ) of i m p u r i t y - i n d u c e d - d i s o r d d r i n g (IID) in GaAs- A l X G a l - 2 s SLs and quantum well structures (QWS), there have been several attemuts to investigate this ohenomenon us in^ ion imnlantation and subsequent annealings
(2-5). However, unlike the two other known methods of imourity introduction, thermal diffusion (6-8) and dooin? durinp growth (9,10), the use of ion imulantation war- rants a better understandin? of the damage influence on Al/Ga interdiffusion.
Gavrilovic et a1 (11) from a study of several dooant and non-dooant jmurity imolants in SLs have suggested that implant damage alone would suffice to promote composi- tional disordering. At the same time several recent renorts (12-15) on active Si do- oant implants in SLs reveraled a highly imulantation process-denendent behavior for interdiffusion. In the work described here, as it will be clear later on, the con- ditions for implants (nature of the snecjes and the implant temnerature) are so chosen as to allow a senerate investigation of damage influence cn interdiffusion in the absence of impurity charge associated effects.
EXPESIYENTAL
2 7 +
Electrically inactive isoelectronic elements 3 1 ~ + and A1 , belonpinv to g r o u ~ I1 and groun 111, and nossessin~ atomic passes close to 2 8 ~ i + were chosen for imolants.
The imolantations were carried out at Z5"C and 250°C (TimD1) jn 3 0 oeriod CaAs- A10.3GaOe7As SLs (L 2. 8OA and LZ 'L qPA) grown by MBE over a 'L 1um thick GaAs buffer
layer on a S1 CaAs a ~ r ) substrate. The energy and dose conditions for the imolants were Inn keV and 1x1015 i o n ~ . c m - ~ , res~ectively. All imnlanted layers and control sarrles (as-grovn) vere annealed at 85C°C (Tannl) using previously reported (10)
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987520
C5-l l 4 J O U R N A L D E PHYSIQUE
close contact configuration nrocedure for durations (tannl) un to 6 h. As is descri- bed below, several characterization techniaues have been emoloyed to monitor the evo- lution in inbetdiffusion.
RESULTS
Using Raman scatterinp. measurements (5145i liAe of Ar+ laser) an estimate of P+
imnlant generated damage in SLs is made in cornoarison with unimolanted as-prown SL and also similarlly im~lanted (at 25'~) bulk GaAs (fig. I). As shown in fig. 1 the as-grown SL exhibits a clearly resolved L0 phonon Deak of GaAs (wells) as well as GaAs-like and AlAs-like L0 phonon peaks belonging to the barrier layers. The presen- ce of usually forbidden PO phonon is a consequence of leakage in our backscattering arrangement. On the other hand, the emergence ofa broad phonon band known as DATA
(Disorder activated transverse acoustic) in im~lanted SLs (also in bulk GaAs) is a definite indication of the presence of implant damage. Additionally, the presence of damage in SLs is further confirmed by the lower frequency shifts, though small, of GaAs L0 and AlAs-like L0 phonon bands. Com~aring the intensity ratios of DATA
to L0 bands, we further conclude that the 25'~ implanted SL contains heavier damage and that its density is much inferior to the level of amorphization. Also considering that the depth ex~lored by Raman measurements (is about the same as Rp
". 900A), we further infer, in confirmation with ~reviously published data (5,13) that SLs are more damage resistant than bulk GaAs.
Fig. 2 shows the peak shiftsof300K photoluminescence spectrarecorded on SLs im- planted with 31P+ and 2 7 ~ 1 + and annealed at 850'~ for periods UD to 6 h. The high stability of as-grown SLs to these anneal treatments can also be witnessed in this figure. The two important features to be remarked here are as follows : i) larger peak shifts for 2 5 ' ~ implantedSLs than those at 250°c, and ii) low efficiency of in- termixing with a tendency to saturation for Al+ implants while those of P+ exhibit a continuous increase in AE with anneal tim:. ConsiQering that the same amount of damage must have been introduced for both P and A1 implants (similar masses and identical impfant ~onditions), the observation (ii) suggests a distinct anneal be- havior for P, a non matrix element, although electrically inactive.
DISCUSSION
To learn more on the nature of implant damage induced influence, we have analy- sed P+ implanted and annealed S1,s for A1 (matrix constituent) and P depth dis- tributions. These distributions shown in fig. 3 are obtained by employing Auger elec- tron spectroscopy (coupled to Ar+ ion s~uttering) for A1 and secondary ion mass spectroscopy (with CS+ primary beam) for P.
All the AES-A1 distributions of fig. 3 represent typical cases of partial mi- xing achieved auring this work. But focusing on the major objectives of the uresent study, the following remarks can be made on the depth evolution of A1 distributions with implant damage and annealing gonditions. The decrease in A1 oscillations confi- ned to a depth less than Rp (". 900A) in as-implanted SL is a consequence of colli- sional mixing during implantation.
On the other hand, a further decrease in Al oscillations, visibly extending to depths for beyond Rp is essentially a consequence of anneal duration (2 or 6 h at 850'~) and the density of damage prior to anneals ( 2 5 " ~ or 250'~ implants), Fof; example, the long range influence on interdiffusion occuring at depths of about 5000A can be evi- denced from a significant decrease in AI oscillations in the first grown layers of SLs (see 6 h annealed SLs).
The aboye results on A1 depth distributions clearly indicate a diffusive nature of the species influencing Al/Ga interdiffusion. However the identical SIEIS recorded depth distributions of P (also shown in fig. 4) before and after 6 h anneal clearly rule out the possibility of P migration to Dromote interdisfusion. Consequently, the results of fig, 4 unambiguously confirm the orominent role of implant damage and its e~olution during prolonged anneals to induce interdiffusion at higher depths (>RP) in the SLs. Al/Ga interdiffusion in implanted G ~ A S - A ~ , G ~ ~ _ ~ A S SLs is a complex phe- nomenon involving the participation of little known defect-impurity interactions.
Even though all our results have contributed to single out, for the first time, the role of implant damage on interdiffusion, they are barely sufficient to propose a convincing model on its nature. Nevertheless, we are of the opinion that the evolu- tion of the implant damage towards well defined struct6ral defects is most likely at the origin of the observations made in this work. Indeed numerous studies (5, 13-15) of transmission electron microscopic ( T ~ ) analysis on Si implanted and annealed SLs have consistently reported the detection of a high density of structural defects
(dislocation loops). Recently Guido eta1 Q6)have proposed the contribution of one such structural defect to explain intermixing achieved in very low dose Si implanted SLS (below a critical value for the observationofhpuitycharge associated effects) after long duration anneals. Besides, in addition to implant damage, the role of mis- fit strain, for example P on As site as compared to AI the matrix element, cannot al- so be ignored. Indeed, as is seen here, some recent reports (4,17) on the implants of matrix elements, Ga and As in GaAs-AlXGal-,As SLs, also reveal a tendency to sa- turation at a low degree of intermixing.
CONCLUSIONS
In conclusi.on, by performing the implants of isoelectronic elements like P and Al, we have investigated the influence of damage on interdiffusion in the absence of
impurity charge associated effects. Besides, by carrying out the implants at two distinct temperatures to generate different damage densities for each implanted spe- cies, we have unambiguously proved the role of implant damage and its depth dependent influence. These results are tentatively explained as a conseaoence of the evolution in structural defects in the presence of strain under prolonged anneals.
The authors are grateful to Dr F. Alexandre for kindly supplying the MBE grown structures investigated in this work.
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C5-116 JOURNAL DE PHYSIQUE
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. . . . . .. . Imp[. arnorphued bulk GaAs -as grown SL
1
-- Implanted SL(Tmpl-25-C)WAVE NVMBER(m-') -.
Fig. I : Room temperature Raman sDectr9 recorded on as-grown unim~lanted and P implanted SLs at 25'~ and 250°C. A spec- trum belonging to bulk GaAs amorphized by a similar implant (at 25'~) is also shown for comparison.
W
a ,CO- 100ke~,l=i0'~~ or AI'
ANNEAL TIME (min)
Fig. 2 : The shift of 300K PL peak ener- gy (AE) as a function of anpeal duration at 850°C for as-grown and P or A1 im- planted SJ.s at 2S°C and 250°C. The ar- row on the ordinate locates the PL peak shift corresponding to average A1 comDo- sition expected in a completely alloy mixed structure.
Fig. 3 : The evolution in A1 (AES-A1 signal ; left ordinate) and P (SIMS-P ; right ordinate) d e ~ t p distributions in SLs im~lanted with P at 25'~ or 250°C, and annealed at 850°C for varied dura- tions. The dotted and continuous lines representing P distributions are recor- ded before (as-implanted at 25"C), and after a 850°C - 6 h anneal. Note also the depth variation of A1 distributions with anneal time.
DEPTH (A)
