Journal ArticleThe use of surfactants to control specific aspects of the vapor-phase epitaxial growth process is  beginning to be studied for both the elemental and III/V semiconductors. To date, most reported  surfactant effects for semiconductors relate to the morphology of the growing films. However,  semiconductor alloys with CuPt ordering exhibit much more dramatic effects. The change in the  CuPt order parameter induced by the surfactant translates into a marked change in the band-gap  energy. Previous work concentrated on the effects of the donor tellurium. Te is less than ideal as a  surfactant, since the change in band-gap energy is coupled to a large change in the conductivity.  This letter presents the results of a study of the effects of an isoelectronic surfactant on the ordering  process in GaInP. Sb has been found to act as a surfactant during organometallic vapor-phase  epitaxial growth. At an estimated Sb concentration in the solid of 1_x0002_10_x0003_4, order is eliminated, as  indicated by the band-gap energy. Surface photoabsorption _x0002_SPA_x0003_ data indicate that the effect is due  to a change in the surface reconstruction. Adding Sb leads to attenuation of the peak at 400 nm in  the SPA spectrum associated with _x0004_1¯ 10_x0005_ P dimers. The addition of Sb during the growth cycle has  been used to produce a heterostructure with a 135 meV band-gap difference between two layers with  the same solid composition

Stringfellow, Gerald B.

English

The University of Utah: J. Willard Marriott Digital Library

Band-gap control of GaInP using Sb as a surfactantJ. K. Shurtleff, R. T. Lee, C. M. Fetzer, and G. B. Stringfellowa)College of Engineering, University of Utah, Salt Lake City, Utah 84112✂Received 20 May 1999; accepted for publication 29 July 1999✄The use of surfactants to control specific aspects of the vapor-phase epitaxial growth process isbeginning to be studied for both the elemental and III/V semiconductors. To date, most reportedsurfactant effects for semiconductors relate to the morphology of the growing films. However,semiconductor alloys with CuPt ordering exhibit much more dramatic effects. The change in theCuPt order parameter induced by the surfactant translates into a marked change in the band-gapenergy. Previous work concentrated on the effects of the donor tellurium. Te is less than ideal as asurfactant, since the change in band-gap energy is coupled to a large change in the conductivity.This letter presents the results of a study of the effects of an isoelectronic surfactant on the orderingprocess in GaInP. Sb has been found to act as a surfactant during organometallic vapor-phaseepitaxial growth. At an estimated Sb concentration in the solid of 1 10✁4, order is eliminated, asindicated by the band-gap energy. Surface photoabsorption ✂SPA✄ data indicate that the effect is dueto a change in the surface reconstruction. Adding Sb leads to attenuation of the peak at 400 nm inthe SPA spectrum associated with☎1¯10✆P dimers. The addition of Sb during the growth cycle hasbeen used to produce a heterostructure with a 135 meV band-gap difference between two layers withthe same solid composition. © 1999 American Institute of Physics. ✝S0003-6951✂99✄03539-1✞Atomic-scale ordering to produce the CuPt structure fre-quently occurs in Ga0.52In0.48P layers grown by organometal-lic vapor-phase epitaxy ✂OMVPE✄ on ✂001✄-oriented GaAssubstrates.1,2 The alternating surface stresses resulting fromthe formation of rows of☎1¯10✆-oriented phosphorous dimerson the (2 n)-reconstructed ✂001✄ surface thermodynam-ically stabilize the variants of the CuPt structure with order-ing on the ✂1¯11✄ and (11¯1) planes.1–3One of the factors having a strong effect on ordering isdoping. Several studies in GaInP have demonstrated a con-nection between ordering and doping as the electron ✂orhole✄ concentration is varied.4–7 For Si and Zn, the effect hasbeen attributed to diffusion in the bulk.4 On the other hand,Te added during OMVPE growth of GaInP was observed toact as a surfactant, dramatically increasing the☎1¯10✆stepvelocity, which resulted in the growth of disorderedmaterial.5–7 This is one of the rare examples of surfactanteffects during OMVPE growth resulting in a major change inthe semiconducting properties of the epilayer.Somewhat different surfactant effects related to the mor-phology of highly strained layers have been the object ofstudy in both elemental8,9 and III/V semiconductors.10,11 Theaddition of dopants during molecular beam epitaxy ✂MBE✄growth has been shown to affect both adatom attachment atstep edges12,13 and surface reconstruction.14 The addition ofthe isoelectronic surfactant As has been shown to modify thesurface reconstruction of cubic GaN grown by MBE.15The ordering phenomenon in semiconductor alloys is ofconsiderable practical interest, because CuPt ordering has alarge effect on the materials properties, e.g., the band-gapenergy is found to be 160 meV lower in partially orderedGa0.52In0.48P than in disordered material of the samecomposition.16 The effect of the surfactant Te on the orderparameter, and hence, the band-gap energy, raises the possi-bility of producing heterostructures and elaborate multilayerstructures required for the most advanced devices by simplymodulating the concentration of a surfactant during growth.This would be particularly powerful if the surfactant did notresult in the loss of control of the Fermi-level position in thestructure.The purpose of this work is to demonstrate that the iso-electronic element Sb has a dramatic effect on the order pa-rameter and, hence, the band-gap energy in GaInP grown byOMVPE. The elimination of CuPt ordering for a tiny Sbconcentration is correlated with the loss of☎1¯10✆P dimerson the surface, as indicated by surface photoabsorption✂SPA✄ measurements. Disorder-on-order heterostructureswere grown by simply modulating the flow rate of the Sbprecursor during growth. Since Sb is isoelectronic with P,this surfactant enables the independent control of the bandgap and the conductivity of the individual layers in complexstructures.Ga0.52In0.48P layers were grown in a horizontal, atmo-spheric pressure OMVPE system17 directly on semi-insulating GaAs substrates without GaAs buffer layers. Bothsingular ✂001✄ and vicinal 3B✟✝3° toward the (111)B direc-tion✞ orientations of the substrates were used. The substrateswere prepared by standard degreasing followed by a 1 minetch in a 12H2O:2NH4OH:1H2O2 solution. They were rinsedfor 5 min in deionized water, and blown dry with filtered N2before being loaded directly into the reactor. Trimethylgal-lium at 7 °C and ethyldimethylindium at 15.9 °C were usedas the group III precursors. Tertiarybutylphosphine ✂TBP✄ at✠7 °C was used as the group V precursor. Triethylantimony✂TESb✄ at ✠7 °C was used as the surfactant precursor. Pd-diffused hydrogen was used as the carrier gas. All of thelayers were grown at a temperature of 620 °C with a V/IIIratio of 40 and a total flow rate of 5500 ml/min. The growtha✡Electronic mail: stringfellow@ee.utah.eduAPPLIED PHYSICS LETTERS VOLUME 75, NUMBER 13 27 SEPTEMBER 199919140003-6951/99/75(13)/1914/3/$15.00 © 1999 American Institute of PhysicsDownloaded 10 Oct 2007 to 155.97.12.90. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsprate was approximately 0.6 ✝m/h. In order to obtain lattice-matched samples, with a mismatch of ☎0.1% as confirmedby x-ray diffraction measurements, the Ga-to-In ratio had tobe changed from 1.22 for undoped Ga0.52In0.48P layers to1.44 for layers with Sb. The surface morphologies of thelayers were mirror like as determined by Nomarski phasecontrast optical microscopy. Photoluminescence ✂PL✄ mea-surements were done at 19 K. The 488 nm line of an Ar✆laser with a power of 10 mW focused to a 0.5 mm2 spot wasused to excite the samples. The PL signal was dispersed witha SPEX monochromator and detected with a photomultipliertube using standard lock-in amplifier techniques. A SPA sys-tem attached to the OMVPE reactor was used to make in situmeasurements of bonding on the GaInP surface.18 Chopped,p-polarized light from a 150 W Xe lamp irradiated the sur-face in the direction of the gas flow at an incident angle ofapproximately 70°. The reflected light was dispersed with acompact monochromator and detected with a Si PNN✆ pho-todiode using standard lock-in amplifier techniques. The fol-lowing procedure was used for the SPA measurements. Afterdeposition of the GaInP layer, the temperature of the samplewas reduced to 520 °C. With TBP flowing through the reac-tor, the reflectivity of the group V-terminated surface wasthen measured in 2 nm steps with a 1 s integration time ateach step. The TBP flow was then stopped and the surfacewas allowed to stabilize for 7 min. The reflectivity of thegroup III-terminated surface was then measured over thesame wavelength range. This procedure was performed withthe incident light parallel to the 1¯10✁and ✞110✟ directionsfor both undoped layers and layers with Sb. The difference inthe reflectivity between the group V- and group III-terminated surfaces, normalized by the group III surface, istermed the SPA difference spectrum. The SPA anisotropyspectrum is the difference between the 1¯10✁and✞110✟SPAdifference spectra.Figure 1✂a✄shows the PL spectrum for an orderedGa0.52In0.48P layer grown on a vicinal (3B✠ ) substrate withoutSb. Figure 1✂b✄ shows the PL spectra for a layer grown withthe addition of a small amount of Sb. The peak energies forthe undoped layer and the layer with Sb are 1841 and 1972meV, respectively, indicating that the layers without Sb arehighly ordered, but the layers are essentially disordered whengrown with Sb present. The 132 meV difference in the band-gap energies indicates the large difference in degree of CuPtordering between the two layers. The PL spectra forGa0.52In0.48P layers grown with and without Sb on singularsubstrates are shown in Figs. 1✂c✄ and 1✂d✄, respectively.Clearly, the addition of a small quantity of Sb during growth,estimated to be 1✡10☛4 from the vapor-phase compositionand the Sb distribution coefficient in GaInPSb alloys,19 wassufficient to disorder the Ga0.52In0.48P layers.Sb as a donor, when added during the MBE growth of Siand Si/Ge alloys, is known to accumulate at thesurface.8,9,12,13 A similar effect is expected for Sb added dur-ing the OMVPE growth of GaInP. The large size of Sb rela-tive to P gives rise to a large positive deviation from idealmixing behavior, yielding a small solubility in GaInP.20,21 Inaddition, the volatility of Sb is much less than that of P.These two factors suggest that Sb is likely to accumulate atthe surface during growth.22Figure 2 shows the SPA anisotropy spectra for undopedlayers and layers grown with Sb. The results indicate a dra-matic change in the surface reconstruction induced by theaddition of Sb to the system. Previous SPA studies showedthat the intensity of the peak at 400 nm in SPA anisotropyspectra directly correlates to the concentration of 1¯10✁Pdimers on the surface.17,18,23 Comparison of the spectra forthe undoped Ga0.52In0.48P layers and layers with Sb clearlyindicates that the P dimer concentration on the surface of thesamples grown with Sb present has been significantly re-duced. This is experimental evidence that an isoelectronicelement, such as Sb, can act as a surfactant to change thesurface reconstruction of a III/V semiconductor layer duringOMVPE growth.Since the 1¯10✁P dimers produce the surface thermody-namic driving force for formation of the CuPt structure dur-ing growth, it is not surprising that the removal of 1¯10✁Pdimers by the addition of Sb also eliminates ordering. TheseFIG. 1. 20 K PL spectra for undoped, ordered Ga0.52In0.48P layers ☞a✌ anddisordered layers grown with the addition of TESb ☞b✌ on vicinal (3B) GaAssubstrates and layers grown without☞c✌and with TESb☞d✌on singular☞001✌GaAs substrates.FIG. 2. SPA anisotropy spectra for Ga0.52In0.48P layers grown with andwithout Sb.1915Appl. Phys. Lett., Vol. 75, No. 13, 27 September 1999 Shurtleff et al.Downloaded 10 Oct 2007 to 155.97.12.90. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jspresults confirm previous observations that the degree of orderin Ga0.52In0.48P layers is directly related to the P dimerconcentration.4–7,23 The lower volatility of Sb, relative to P,and the rejection of Sb from the solid lead to the accumula-tion of Sb at the surface. The elimination of☎1¯10✆P dimersmay be due to the formation of a second layer of Sb at thesetemperatures.The ability to control the ordering and, thus, the band-gap energy of GaInP layers by the addition of Sb duringgrowth suggests the possibility of producing heterostructuresand quantum wells. To grow a disorder-on-order heterostruc-ture, the surface of the undoped, ordered Ga0.52In0.48P layergrown first was exposed to TBP and TESb for 5 min, withoutgrowth, to allow Sb to accumulate. The disordered layer con-taining Sb was then grown. Figure 3 shows the PL spectrumfor a disorder-on-order heterostructure grown by this proce-dure. A remarkable difference in the band-gap energy be-tween the two layers of 135 meV was achieved. This is ademonstration of a potentially powerful method for the pro-duction of atomically engineered structures for advancedelectronic and photonic devices. The ability to independentlymodulate the band gap and the Fermi-level position is thekey to the potential usefulness of this technique. The 135meV band-gap discontinuity is more than 5 kT at room tem-perature, which should be sufficient for many devices.The addition of Sb, from the pyrolysis of TESb, duringthe OMVPE growth of Ga0.52In0.48P essentially eliminatesthe CuPt ordering observed in layers grown without Sb. Theloss of ordering leads to a 132 meV increase in the band-gapenergy, as judged from the 20 K PL peak positions. Theresults of in situ SPA analysis of the surface indicate that thisis due to a change in the surface reconstruction induced bythe Sb. The results indicate that modulation of the TESb flowrate can be used to control the GaInP band-gap energy. Asingle heterostructure gives PL peaks from the two layers,grown with and without Sb present, that differ by 135 meV.This demonstrates the use of an isoelectronic surfactant tomodulate the band-gap energy of a material grown by OM-VPE. Since Sb is isoelectronic with P and is present at smallconcentrations, the modulation in band-gap energy is accom-plished with no effect on either the solid composition or theFermi-level position. It is anticipated that surfactant Sb canalso be used to produce more complex structures, such asquantum wells.The authors wish to thank the Department of Energy✂growth and photoluminescence results✄ and the NationalScience Foundation✂surface photoabsorption measurements✄for financial support of this work.1G. B. Stringfellow, in Common Themes and Mechanisms of EpitaxialGrowth, edited by P. Fuoss, J. Tsao, D. W. Kisker, A. Zangwill, and T.Kuech  Materials Research Society, Pittsburgh, PA, 1993✁, pp. 35–46.2G. B. Stringfellow, in Thin Films: Heteroepitaxial Systems, edited by M.Santos and W. K. Liu World Scientific, Singapore, 1998✁, p. 64.3S. B. Zhang, S. Froyen, and A. Zunger, Appl. Phys. Lett. 67, 3141  1995✁.4R. T. Lee, C. Y. Fetzer, K. Shurtleff, Y. Hsu, G. B. Stringfellow, and T. Y.Seong, J. Electron. Mater. to be published✁.5S. H. Lee, C. Y. Fetzer, G. B. Stringfellow, D. H. Lee, and T. Y. Seong,J. Appl. Phys. 85, 3590  1999✁.6S. H. Lee, T. C. Hsu, and G. B. Stringfellow, J. Appl. Phys. 84, 2618 1998✁.7S. H. Lee, C. Y. Fetzer, and G. B. Stringfellow, J. Cryst. Growth 195, 13 1998✁.8M. Copel, M. C. Reuter, E. Kaxiras, and R. M. Tromp, Phys. Rev. Lett.63, 632  1989✁.9E. Tournie and K. H. Ploog, Thin Solid Films 231, 43  1993✁; D. Reink-ing, M. Kammier, M. Horn-von Hoegen, and K. R. Hofmann, Appl. Phys.Lett. 71, 924 1997✁.10 J. Massies, N. Grandjean, and V. H. Etgens, Appl. Phys. Lett. 61, 99 1992✁; J. E. Cunningham, K. W. Goossen, W. Jan, and M. D. Williams,J. Vac. Sci. Technol. B 13, 646 1994✁.11B. R. A. Neves, M. S. Andrade, W. N. Rodrigues, G. A. M. Safar, M. V.B. Moreira, and A. G. de Oliveira, Appl. Phys. Lett. 72, 1712  1998✁.12D. Kandel and E. Kaxiras, Phys. Rev. Lett. 75, 2742 1995✁.13C. W. Oh, E. Kim, and Y. H. Lee, Phys. Rev. Lett. 76, 776 1996✁.14H. Oigawa, M. Wassermeier, J. Behrend, L. Daweritz, and K. H. Ploog,Surf. Sci. 376, 185 1997✁.15H. Okumura, H. Hamaguchi, G. Feuillet, Y. Ishida, and S. Yoshida, Appl.Phys. Lett. 72, 3056  1998✁.16L. C. Su, I. H. Ho, N. Kobayashi, and G. B. Stringfellow, J. Cryst. Growth145, 140 1994✁.17H. Murata, I. H. Ho, L. C. Su, Y. Hosokawa, and G. B. Stringfellow, J.Appl. Phys. 79, 6895  1996✁.18H. Murata, I. H. Ho, T. C. Hsu, and G. B. Stringfellow, Appl. Phys. Lett.67, 3747 1995✁.19G. B. Stringfellow, Organometallic Vapor Phase Epitaxy: Theory andPractice, 2nd ed.  Academic, San Diego, CA, 1999✁, p. 59.20G. B. Stringfellow, J. Cryst. Growth 27, 21 1974✁.21M. J. Jou, D. H. Jaw, Z. M. Fang, and G. B. Stringfellow, J. Cryst. Growth190, 208  1990✁.22R. Kaspi, K. R. Evans, D. C. Reynolds, J. Brown, and M. Skowronski,Mater. Res. Soc. Symp. Proc. 379, 79 1995✁.23T. C. Hsu, Y. Hsu, and G. B. Stringfellow, J. Cryst. Growth 193, 1  1998✁.FIG. 3. 20 K PL spectrum for a GaInP disorder-on-order heterostructuregrown by modulating the TESb flow during growth.1916 Appl. Phys. Lett., Vol. 75, No. 13, 27 September 1999 Shurtleff et al.Downloaded 10 Oct 2007 to 155.97.12.90. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

Bandgap control of GaInP using Sb as a surfactant

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Bandgap control of GaInP using Sb as a surfactant

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