An efficient way to improve compositional abruptness at the GaAs on GaInAs interfaceE. Chirlias, J. Massies, J. L. Guyaux, H. Moisan, and J. Ch. Garcia Citation: Applied Physics Letters 74, 3972 (1999); doi: 10.1063/1.124240 View online: http://dx.doi.org/10.1063/1.124240 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/74/26?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Cross-sectional scanning tunneling microscopy and spectroscopy of InGaP/GaAs heterojunctions Appl. Phys. Lett. 84, 227 (2004); 10.1063/1.1638637 Interfacial stability and structure in InAs/GaAs(111)A heteroepitaxy: Effects of buffer layer thickness and filmcompositional grading Appl. Phys. Lett. 77, 3352 (2000); 10.1063/1.1327275 Interface control and band offset at the Ga 0.52 In 0.48 P on GaAs heterojunction J. Vac. Sci. Technol. B 18, 2096 (2000); 10.1116/1.1305285 X-ray photoemission characterization of interface abruptness and band offset of Ga 0.5 In 0.5 P grown on GaAs J. Appl. Phys. 84, 2127 (1998); 10.1063/1.368357 Growth, doping, and etching of GaAs and InGaAs using tris-dimethylaminoarsenic J. Vac. Sci. Technol. B 15, 159 (1997); 10.1116/1.589242

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An efficient way to improve compositional abruptness at the GaAson GaInAs interface

E. Chirlias, J. Massies,a) J. L. Guyaux, H. Moisan, and J. Ch. GarciaLaboratoire Central de Recherches Thomson–CSF Domaine de Corbeville, 91404 Orsay, cedex, France

~Received 25 March 1999; accepted for publication 6 May 1999!

Indium surface segregation during the growth of Ga12xInxAs by chemical beam epitaxy isevidenced in real time by reflection high-energy electron diffraction. An efficient way to suppressthe compositional broadening of GaAs on the GaInAs interface resulting from the In segregationeffect is proposed. It consists in using the chemical reaction of AsCl3 molecules at the surface,which is shown to etch layer by layer the Ga12xInxAs alloy. Monolayer etching precision is thusobtained and used to eliminate the In accumulation at the GaInAs surface and the related interfacebroadening. ©1999 American Institute of Physics.@S0003-6951~99!03526-3#

In the last ten years, surface segregation of the less-bonded element III in ternary III,III8–V semiconductor al-loys has been evidenced by using various techniques.1–10It isnow well established that this phenomenon inherently limitsthe formation of abrupt interfaces. Because of the huge de-velopment of device applications of GaInAs/GaAs hetero-structures, most of the studies of surface segregation havebeen devoted to this prototypical III–V semiconductorsystem.3–10 Indeed, both its optoelectronic and microwaveapplications mainly rely on quantum heterostructures forwhich compositionally abrupt interfaces are highly desired.Several growth procedures have been proposed to improveinterface abruptness. The most natural way is to kineticallyhinder the In surface segregation mechanism during thegrowth of GaInAs. This can be done by either decreasing thegrowth temperature4,8,10 or increasing the growth rate11 orthe V/III flux ratio.4,8 However, varying the growth param-eters in such a way is detrimental to the overall optoelec-tronic properties of the material.4 Moreover, the best set ofgrowth parameters in terms of In segregation reduction is farfrom the optimum growth conditions of GaAs, always asso-ciated with GaInAs in structures of interest for device appli-cations. Actually, the use of different sets of growth param-eters for quantum well and barrier materials is very difficultto implement in a growth process. This is particularly truefor the growth temperature, which can hardly be varied witha short time constant. Significant temperature modificationnecessitates, in fact, rather long growth interrupts. A moresimple and elegant approach has been proposed by Kaspi andEvans to eliminate the compositionally graded region at theGaInAs on GaAs interface.9 It consists in predepositing, be-fore the start of GaInAs growth, an amount of In correspond-ing to the In floating layer formed at the steady state for agiven set of growth parameters. The In floating layer beingpreestablished, the compositionally graded GaInAs layer re-sulting from its buildup in the usual growth procedure isavoided.9 However, as for standard growth conditions,GaInAs is covered by In floating at the surface, which isprogressively incorporated during the subsequent growth of

GaAs, eventually leading to a broadened GaAs on GaInAsinterface. The abruptness of this particular interface is hardto improve. Up to now, the only way is to interrupt thegrowth before growing GaAs and to increase the temperaturein order to desorb the excess In at the GaInAs surface.12

However, an adequate set of annealing temperature and timeis difficult to precisely determine, and the control should beexcellent to remove exactly the desired amount of In. More-over, this selective thermal desorption can result in surfaceroughening and overall material quality degradation.12

In this letter, we propose a simple and efficient way toeliminate the In floating layer at the GaInAs surface. It isbased onin situ chemical etching by AsCl3 molecules. It isshown by reflection high-energy electron diffraction~RHEED! that GaInAs chemical etching by AsCl3 proceedslayer by layer with a rate comparable to the usual growth rate@;1 monolayer~ML !/s# and without noticeable rougheningof the surface. The real-time RHEED investigation demon-strates that the In segregated layer is easily removed byAsCl3 even for a very short exposure time~;1 s!.

The experiments have been carried out in a chemicalbeam epitaxy~CBE! environment. GaAs and Ga12xInxAswere grown at 500 °C on a GaAs~001! substrate using tri-ethylgallium ~TEGa!, trimethylindium ~TMIn!, and tris-dimethylamino arsenic~tDMAAs! precursors with standardinjectors. AsCl3 was injected through a nozzle kept at 80 °C.All the gas lines were controlled by pressure regulation. Boththe growth and etching rates were measured in real time byRHEED intensity oscillations. The In mole fraction ofGa12xInxAs was determined by comparing the alloy growthrate and the In incorporation rate deduced from the two-dimensional–three-dimensional~2D–3D! growth-mode tran-sition of InAs on GaAs for which the critical thickness wastaken at 1.7 ML.13 As checked by high-resolution x-ray dif-fraction, this procedure gives the alloy composition within60.1% precision.

When growing by CBE, Ga12xInxAs on GaAs as well asGaAs on Ga12xInxAs @Fig. 1~a!#, the oscillatory period of theRHEED intensity at the beginning of the growth is not con-stant. It decreases or increases for Ga12xInxAs and GaAsgrowth, respectively. The corresponding growth rate gradi-ents are reported in Fig. 1~b!. This behavior is the direct

a!Permanent address: CRHEA/CNRS, rue B. Gregory, Sophia Antipolis,06560 Valbonne, France. Electronic mail: jm@crhea.cnrs.fr

APPLIED PHYSICS LETTERS VOLUME 74, NUMBER 26 28 JUNE 1999

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consequence of a variation of the In atom population at thegrowing surface. Indeed, it is well known that the presenceof In at the growth front modifies the decomposition kineticsof TEGa, resulting in the decrease of the Ga incorporationrate.14,15 The growth rate transients observed in Figs. 1~a!and 1~b! are, in fact, the signature of In surface segregationand of an associated compositional broadening of theinterfaces.15,16

Turning now to in situ etching of GaInAs, Fig. 2 dataclearly show that upon AsCl3 injection, RHEED intensityoscillations are observed, indicating a 2D layer-by-layeretching mode, as for GaAs in similar etching conditions.17

From these type of data corresponding to Ga0.81In0.19As, anAsCl3 gas line pressure regulated at 3 Torr and a substratetemperature of 500 °C, an etching rate of 0.9 ML/s is ob-tained, i.e., identical to the growth rate of the alloy which ishere kept at 0.9 ML/s. No roughening of the surface is ob-served and after a few seconds etch stop, GaAs growth leadsto RHEED oscillations in the same way as after a growthinterrupt. The point is that when the growth of GaAs isstarted after some etching of the Ga12xInxAs layer, nogrowth rate transient is observed, indicating that the In float-ing layer at the surface has been suppressed. This is exem-plified in Fig. 3, which shows RHEED intensity oscillationsrecorded during the growth of Ga0.81In0.19As on GaAs@Fig.

3~a!#, AsCl3 etching of 3 ML @Fig. 3~b!#, and subsequentgrowth of GaAs@Fig. 3~c!#. It is clear from Fig. 3~c! that theorigin of the growth rate transient, i.e., the In floating layer,has disappeared. To confirm this, we have used another ap-proach originally proposed by Gerard.3 It is based on thecomparison of the critical thickness for the InAs 2D–3Dgrowth-mode transition when grown directly on GaAs or onGaInAs layers. This method has been successfully used toquantify the amount of In segregated at the GaInAssurface.3,5,8The principle is that both the In segregated at thesurface of GaInAs and the amount of the subsequently de-posited InAs layer necessary to provoke islanding contributeto the actual InAs thickness. Therefore, if an In floating layeris present prior to InAs deposition, the InAs 2D–3D growth-mode transition appears earlier. Such a transition is easilydetected in real time by RHEED, recording either the specu-lar beam or a Bragg beam intensity variation.18 An abrupt

FIG. 1. ~a! RHEED specular beam intensity oscillation recorded during theCBE growth at 500 °C of Ga0.81In0.19As on GaAs~upper curve! and GaAson Ga0.81In0.19As ~lower curve!. Note the growth transient at both interfac-es. ~b! Growth rate gradients for Ga0.81In0.19As grown on GaAs~triangles!and GaAs grown on Ga0.81In0.19As ~circles! as deduced from the above data.

FIG. 2. RHEED specular beam intensity oscillation recorded during theCBE growth of 29 ML Ga0.81In0.19As on GaAs and subsequent etching byAsCl3 ~substrate temperature: 500 °C!.

FIG. 3. RHEED specular beam intensity oscillation recorded during thefollowing sequence:~a! CBE growth of Ga0.81In0.19As on GaAs;~b! 3 MLetching by AsCl3; and ~c! GaAs regrowth~substrate temperature: 500 °C!.

3973Appl. Phys. Lett., Vol. 74, No. 26, 28 June 1999 Chirlias et al.

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intensity decrease or increase is observed at the specular andBragg positions, respectively.18 This is illustrated in Fig. 4,where data corresponding to typical growth situations arereported. Figure 4~a! concerns the growth of InAs on GaAsat 500 °C and is used as a reference for a starting surface freeof accumulated In atoms. Although the critical thickness forislanding is clearly detected on both the specular and Braggsignals, we have taken the onset of the Bragg intensity in-crease as the signature of the 2D–3D transition. With theTMIn gas line pressure set at the same value as forGa0.81In0.19As growth ~0.34 Torr!, it occurs for a depositiontime of 9.060.5 s ~mean value for several experiments!. Itcorresponds to 1.760.1 ML of InAs.13 When comparingwith the growth of InAs on top of;90 Å of Ga0.81In0.19As@Fig. 4~b!#, a drastic shrinkage of the time needed for island-ing is observed (3.560.3 s). Taking the critical thickness at1.7 ML, this corresponds to;1 ML of In segregated at theGa0.81In0.19As surface, in agreement with what is generallyreported in the same growth temperature range.5,9 If now anAsCl3 etching step of;1 s ~;1 ML! is inserted betweenGa0.81In0.19As and InAs growth, the deposition time of InAsnecessary to observe the 2D–3D transition is 8 s@Fig. 4~c!#,i.e., very similar to the one corresponding to InAs on GaAs.Increasing the etching time from 1 to 15 s does not signifi-

cantly change the critical thickness deposition time. Themean value obtained is 8.060.5 s. Although this time isslightly shorter than the one measured for InAs on GaAs,probably due to the fact that Ga0.81In0.19As is in a strainedstate compared to GaAs, this confirms that even a very shortpulse of AsCl3 is sufficient to remove the excess In atoms atthe GaInAs surface, and therefore, the associated composi-tional broadening at the GaAs on GaInAs interface.

In summary, we have shown that AsCl3 can be used tochemically etch GaInAs alloys in a layer-by-layer mode withan etching rate in the monolayer per second range. We havedemonstrated by real-time RHEED investigation that theshort pulse of AsCl3 etching is sufficient to remove the Inexcess surface layer formed during the growth of GaInAs asa consequence of In segregation. This simple procedureeliminates the main mechanism at the origin of a broadenedcomposition profile at the GaAs on GaInAs interface.

The authors would like to thank X. Marcadet for helpfuldiscussions and J. Nagle for strong support and interest. Oneof the authors~J.M.! gratefully acknowledges Thomson–CSF/LCR for kind hospitality during the performance of thiswork and N. Grandjean and M. Leroux for critical reading ofthe manuscript.

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FIG. 4. RHEED specular beam intensity~continuous line! and Bragg inten-sity ~dashed line! variations recorded during the growth of~a! InAs onGaAs,~b! InAs on Ga0.81In0.19As, and~c! InAs on Ga0.81In0.19As, but with amonolayer AsCl3 etching step at the interface. In each case the 2D–3Dgrowth-mode transition is indicated by a vertical dashed line~substrate tem-perature: 500 °C!.

3974 Appl. Phys. Lett., Vol. 74, No. 26, 28 June 1999 Chirlias et al.

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