The early stages of ZnSe heteroepitaxy on Si(100), Si(100):As and GaAs(100) are compared and contrasted, based on results of scanning tunneling microscopy and photoemission spectroscopy. High Se reactivity with the substrate constituents leads to bulk phase formation which is detrimental to heteroepitaxy. As-termination of Si(100) not only passivates the surface, but also provides an ideal buffer for ZnSe overgrowth. Lacking a similar buffer layer, stoichiometric control of the GaAs(100) surface is investigated to find a means for controlled heteroepitaxy

Biegelsen, D. K.

Bringans, R. D.

Northrup, J. E.

Swartz, L. -E.

English

DigitalCommons@USU

Scanning Microscopy Volume 8 Number 4 Article 14 12-13-1994 ZnSe Heteroepitaxial Growth on Si (100) and GaAs (100) D. K. Biegelsen Xerox Palo Alto Research Center, biegelsen@parc.xerox.com R. D. Bringans Xerox Palo Alto Research Center J. E. Northrup Xerox Palo Alto Research Center L. -E. Swartz Xerox Palo Alto Research Center Follow this and additional works at: https://digitalcommons.usu.edu/microscopy  Part of the Biology Commons Recommended Citation Biegelsen, D. K.; Bringans, R. D.; Northrup, J. E.; and Swartz, L. -E. (1994) "ZnSe Heteroepitaxial Growth on Si (100) and GaAs (100)," Scanning Microscopy: Vol. 8 : No. 4 , Article 14. Available at: https://digitalcommons.usu.edu/microscopy/vol8/iss4/14 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact digitalcommons@usu.edu. Scanning Microscopy, Vol. 8, No. 4, 1994 (Pages 883-888) 0891-7035/94$5.00+ .25 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA ZnSe HETEROEPITAXIAL GROWTH ON Si (100) AND GaAs (100) D.K. Biegelsen .. R.D. Bringans, J.E. Northrup and L.-E. Swartz Xerox Palo Alto Research Center, Palo Alto, CA 94304 (Received for publication June 23, 1994 and in revised form December 13, 1994) Abstract The early stages of ZnSe heteroepitaxy on Si(lOO), Si(lOO):As and GaAs(lOO) are compared and contrasted, based on results of scanning tunneling microscopy and photoemission spectroscopy. High Se reactivity with the substrate constituents leads to bulk phase formation which is detrimental to heteroepitaxy. As-termination of Si(lOO) not only passivates the surface, but also provides an ideal buffer for ZnSe overgrowth. Lacking a similar buffer layer, stoichiometric control of the GaAs(l00) surface is investigated to find a means for controlled heteroepitaxy. Key Words: Heteroepitaxy, As-termination, zinc sele-nide, gallium arsenide, silicon. • Address for correspondence and present address: David K. Biegelsen Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304 Telephone number: (415) 812-4137 FAX number: (415) 812-4140 E-mail: biegelsen@parc.xerox.com 883 Introduction Controlled heteroepitaxial film growth requires that the overlayer proceed through a progression of effective-ly two dimensional structures, The structures are generally metastable. Competing configurations having lower energy must be, if possible, kinetically con-strained. The growth of ZnSe on Si and GaAs presents interesting examples where the chemical configurations can, in principle, be energetically stable at each stage. The crystal grower might then be aligned with nature in achieving the desired goal. In this paper, we contrast the early stages of film evolution for ZnSe on Si(l00) and GaAs(lOO). Results and Discussion The ideally terminated Si(lO0) surface has two sin-gly occupied dangling bonds per surface atom. Dimeri-zation lowers the total energy but leaves the surface highly reactive. One monolayer (ML) of two-fold coor-dinated Se bridging between Si atoms results in a relatively low energy structure (Bringans and Olmstead, 1989) and might be expected to form a passivating layer. In previous work (Bringans et al., 1992), it has been shown that ZnSe deposition directly on Si at ele-vated temperatures results in polycrystalline overgrowth. The reason is that the heat of formation of SiSez is strongly negative. This driving force coupled with the low average coordination of SiSez leads to a diffusion-limited growth of bulk, glassy SiSez at moderate temper-atures. Thus, even in the presence of Zn, the Se ambi-ent converts the Si from an epitaxial template to a non-crystalline substrate. The kinetic barrier separating the metastable Se-monolayer termination from the much lower-energy bulk SiSez is too low to be useful. Depos-iting Zn first (Park and Mar, 1986) or using very low substrate temperatures (Bringans et al., 1992) reduces the reaction but also produces poor epitaxial growth. Arsenic termination of Si(lO0) has also been shown to be energetically very favorable (Uhrberg et al., 1986). Furthermore, there is a high kinetic barrier to SixAsy formation. Most importantly, though, for its use D.K. Biegelson, R.D. Bringans, J.E. Northrup and L.-E. Swartz Si(100):As 2x1 ZnSe(100) 2x1 As Si Si Si Se Zn Se Zn Figure 1. Ball and stick models of (top) As on Si(lOO) and (bottom) ZnSe on GaAs(lO0). The structures are projected along the [0ll] direction. as a template for ZnSe heteroepitaxy, the Si(lOO):As 2xl dimerized surface, shown schematically in Figure 1 (top), is isoelectronic and structurally equivalent to the Se terminated ZnSe(lOO) 2xl surface [Fig. 1 (bottom)]. In both cases, the surface atoms have three electrons per atom available for epitaxial overgrowth. From an inci-dent Zn atom perspective, the Si(lOO):As surface looks like a Se-terminated bulk ZnSe(lOO) surface. Although the dimerized As atoms on Si(lOO) are fully coordinated, the dimer bond can be broken, leaving fewer than two electrons per orbital to contribute to subsequent covalent bonds. It was, therefore, expected (D.J. Chadi, person-al communication) and shown experimentally (Bringans et al., 1992) that ZnSe heteroepitaxy on Si(lOO):As is analogous to growth of chemically similar but lattice mismatched epitaxy, such as ZnSe on ZnS. (Note that one significant difference is that, unlike for polar semiconductor (100) surfaces, single atom height steps can be prevalent on group IV surfaces and can lead to antiphase domains in the II-VI overlayer.) Figure 2 shows the uniform epitaxial growth of a thin overlayer of ZnSe on Si(lOO):As (Bringans et al., 1992). Using energy dispersive X-ray spectroscopy in the transmission electron microscope (TEM), the As monolayer has been shown (Romano et al., 1994) to be pinned to the inter-face even after annealing to 900°C. Thus, the initial 884 and final stages of growth of Si(lOO):As/ZnSe are ener-getically stable. The As monolayer is both a surface and interface passivant. [It is instructive to note that this is not the case for the ( 111) interface. Here also all Si dangling bonds are replaced by doubly occupied, low en-ergy, As lone pairs. All atoms are again fully coordi-nated. However, with no dimer bonds to open, all sur-face orbitals are doubly occupied and only dative bond-ing can occur with any adsorbed species. In the alterna-tive but equivalent view, there is no analogous, isoelec-tronic surface of ZnSe(lll) which can satisfy the elec-tron counting criteria. Therefore, the As ML does not support heteroepitaxy on the (111) surface and the As is a surface passivant only.) We now turn to the evolution of ZnSe growth on GaAs(lO0). Here again, there is a strong thermodynam-ic driving force (high negative enthalpy) for compound formation (e.g., GaSe, Ga2S~ and A82Se3; Li and Pashley, 1994). Another similarity to the growth on Si is the existence of a stable termination of the substrate which should also be energetically favorable as an inter-face. Harrison et al. (1978) first pointed out that elec-tron counting arguments leading to covalent bond satura-tion and interface neutrality usually represent the domi-nant energetic tem1. They further showed that a simple, low energy interface arrangement between binary com-pound semiconductors arises from a 50:50 mixture of re-spective cations or anions. Charge transfer between nearby compensating, over- and under-coordinated pairs leads to interface neutrality and dipole minimization. For the case of ZnSe coverage of GaAs (100), Farrell et al. (1988) have proposed, and Figure 3a shows, a possi-ble configuration where a half monolayer of As-Zn bonds (electron deficient) is compensated by a half monolayer of Se-Ga (electron-rich) bonds. A related possibility, having cation mixing, is shown in Figure 3b. It is now becoming accepted that the dominant GaAs (100) surface reconstruction existing under the usual As-rich growth conditions in molecular beam epitaxy (MBE) is a 2x4 structure consisting of two As-As dimers (Biegelsen et al., 1990; Bressler-Hill et al., 1992; Hashizume et al., 1994) atop a complete Ga layer ["a (2x4) phase"] or over a 3/4 ML Ga layer ["/32(2x4) phase"] as shown in Figures 4a and 4b, respectively. The former would be ideal for the anion-mixed inter-face. Similarly, a /32( 4x2) phase consisting of two Ga-Ga dimers atop a complete As monolayer (Fig.· 4c) would, in principle, be ideal for the inverted ZnSe over-growth as shown in Figure 3b. Unfortunately, for control of crystal growth, the energetics deflect the pathway of film evolution away from the ideal. Although, scanning tunneling micros-copy (STM) shows highly ordered dimerization of the Se-reacted GaAs (100) surface (see Figs. 5a and Sb), ZnSe growth on Si and GaAs Figure 2. TEM cross-section of ZnSe grown on Si(IOO):As showing the abrupt interface and uniform overgrowth (capping layer of a-Si is added during TEM sample preparation). (Reprinted from Bringans et al., 1992) (a) (b} Se Zn Zn Se Se Zn Zn Se As/Se Ga/Zn Ga As As Ga Ga As As Ga Figure 3. Ball and stick models of ZnSe/GaAs(lOO) interfaces with intermixed (a) anion or (b) cation layers. The minus (plus) signs indicate excess (deficient) electron concentration. 885 D.K. Biegelson, R.D. Bringans, J.E. Northrup and L.-E. Swartz r-----------, r-----------, r-----------, I I I I I I I I I • • I I 0---0 I I I I I I I I I I I I I I I I I I I I I L-----------.JI L-----------.1 L-----------.1 (a) a(2x4) (b) P2{2x4) (c) (32(4x2) Figure 4. Ball and stick models of GaAs(lO0) 2x4 and 4x2 reconstructions; (a) a(2x4), (b) ,62(2x4), and (c) ,62(4x2), respectively. The [011) direction is parallel to the vertical axis in (a) and (b) and parallel to the horizontal axis in (c). (Reprinted from Northrup and Froyen, 1994) concurrent X-ray photoemission spectroscopy measure-ments show that the surface is not simply terminated by a 50:50 mixture of Se and As (Biegelsen et al., 1994). An initial uptake of approximately one Se ML occurs, exchanging with 1 ML of As, followed by a slowly in-creasing exchange of Se for As and a concomitant loss of Ga (Biegelsen et al., 1994; Chambers and Sundaram, 1991; Takatani et al., 1992). The STM images in Fig-ure 5 were taken on samples prepared using a Se fluence equivalent to 4 nm thickness of bulk Se. The near-sur-face stoichiometry has been shown to be changing very slowly with fluence in this regime and STM images are independent of the particular fluence. This surface should therefore be representative of the ion -exchanged surface generally found under similar conditions. It has not been possible to determine if the dimers are Se -Se, Se-As or other. In any case, a bulk reaction occurs in 886 the Se -rich regime which undermines the creation of an ideal anion -mixed interface overlying ideal bulk GaAs. Li and Pashley (1994) have inferred from their STM re-sults that the Se surface reaction directly leads to the 3d overgrowth of ZnSe. Note that Tamargo et al. (1988) have inferred from reflection electron diffraction measurements that 2d growth can be achieved on the GaAs( 100) 2x4 surface. This is an important step which must be pursued and clarified. It has been shown empirically that much more uni-form MBE growth of ZnSe on GaAs (100) occurs by initiating deposition in a Zn -rich regime (DePuydt et al., 1987; Gaines et al., 1993; Guha et al., 1993). This would seem to be in keeping with an a(4x2) surface reconstruction suggested by Farrell et al. (1988) and consistent with early STM images of the 4x2 surface (Biegelsen et al., 1990). However, total energy calcu-ZnSe growth on Si and GaAs calculations (Northrup and Froyen, 1994) again predict that the most stable surface structure should be the ~2(4x2) phase, with only 3/4 ML As below the Ga-Ga dimers, and more recent STM experiments (Skala et al., 1993) are interpreted to imply non-a( 4x2) arrangements. Further work is clearly necessary to study the Zn-rich initiation of ZnSe on Ga-rich GaAs (100) surfaces. Conclusions In summary, Se reactivity with Si and GaAs sub-strates leads to disruption of ideal heteroepitaxy. In the case of Si(lOO), an adsorbed As ML both passivates the Si surface and acts as well as an ideal interfacial buffer for II-VI overgrowth. Currently, a similarly strong mechanism has not been observed for stage to stage control of ZnSe growth on GaAs(lO0). However, STM measurements coupled with photoemission spectroscopy should elucidate the tendency toward uniform growth when Zn is dominant during the growth initiation. References Biegelsen DK, Bringans RD, Northrup JE, Swartz L-E (1990) Surface reconstructions of GaAs(l00) ob-served by scanning tunneling microscopy. Phys Rev B 41, 5701-5706. Biegelsen DK, Bringans RD, Northrup JE, Swartz L-E (1994) Selenium- and tellurium-terminated GaAs(lO0) surfaces observed by scanning tunneling microscopy. Phys Rev B 49, 5424-5428. Bressler-Hill V, Wassermeier M, Pond K, Maboudian R, Briggs GAD, Petroff PM, Weinberg WH (1992) Atom-resolved imaging and spectroscopy on the GaAs(OOl) surface using tunneling microscopy. J Vac Sci Technol B 10, 1881-1885. Bringans RD, Olmstead MA (1989) Bonding of Se and ZnSe to the Si(l00) surface. Phys Rev B 39, 12985-12988. Bringans RD, Biegelsen DK, Swartz L-E, Ponce FA, Tramontana JC (1992) Effect of interface chemistry on the growth of ZnSe on the Si(lO0) surface. Phys Rev B 45, 13400-13406. Chambers SA, Sundaram VS (1991) Passivation of GaAs(00l) surfaces by incorporation of group VI atoms: a structural investigation. J Vac Sci Technol B 9, 2256-2262. DePuydt JM, Cheng H, Potts JE, Smith TL, Mo,hapatra SKJ (1987) Growth of undoped ZnSe on (100) GaAs by molecular-beam epitaxy: an investigation of the effects of growth temperature and beam pressure ratio. Appl Phys Lett 62, 4756-4762. Farrell HH, Tamargo MC, de Miguel JL (1988) Mo,lecular-beam epitaxy and atomic-layer epitaxy 887 (a) Figure 5. STM filled state, constant current images of GaAs(lO0):Se surfaces. Lighter gray value indicates higher. (a) 11 nm x 12 nm area; (b) 3 nm x 3 nm area. (Reprinted from Biegelsen et al., 1994) growth mechanisms for ZnSe(lO0) J Vac Sci Technol B 6, 767-768. Gaines JM, Petruzello J, Greenberg BJ (1993) Structural properties of ZnSe films grown by migration enhanced epitaxy. Appl Phys 73, 2835-2840. Guba S, Munekata H, Chang LL (1993) Structural quality and the growth mode in epitaxial ZnSe/GaAs (100). J Appl Phys 73, 2294-2300. Harrison WA, Kraut EA, Waldrop JR, Grant WR (1978) Polar hetero-junction interfaces. Phys Rev B 18, D.K. Biegelson, R.D. Bringans, J.E. Northrup and L.-E. Swartz 4402-4410. Hashizume T, Xue QK, Zhou J, Ichimiya A, Sakurai T (1994) Structures of As-rich GaAs(OOl) 2x4 reconstructions. Phys Rev Lett 73, 2208-2211. Li D, Pashley MD (1994) Interaction of selenium with the GaAs(001)-(2x4)/c(2x8) surface studied by scanning tunneling microscopy. Phys Rev B 49, 13643-13649. Northrup JE, Froyen S (1994) Structure of GaAs (001) surfaces: the role of electrostatic interactions. Phys Rev B 50, 2015-2018. Park RM, Mar HA (1986) Molecular beam epitaxial growth of high quality ZnSe on (100) Si. Appl Phys Lett 48, 529-531. Romano LT, Bringans RD, Knall J, Biegelsen DK, Garcia A, Northrup JE (1994) Atomic rearrangement at the interface of annealed ZnSe films grown on vicinal Si(OOl) substrates. Phys Rev B 50, 4416-4423. Skala SL, Hubacek JS, Tucker JR, Lyding JW, Chou ST, Cheng K-Y (1993) Structure of GaAs(100)-c(8x2) determined by scanning tunneling microscopy. Phys Rev B 48, 9138-9141. Takatani S, Kikawa T, Nakazawa M (1992) Reflection high energy electron diffraction and photo-emission spectroscopy study of GaAs(OOl) surface modi-fied by Se adsorption. Phys Rev B 45, 8498-8505. Tamargo MC, de Miguel JL, Hwang DM, Farrell HH (1988) ZnSe/III-V heterostructures grown in a multichamber MBE system. J Vac Sci Technol B 6, 784-789. Uhrberg RIG, Bringans RD, Bachrach RZ, Northrup JE (1986) Symmetric arsenic dimers on the Si(lOO) surface. Phys Rev Lett 56, 520-523. Editor's Note: All of the reviewer's concerns were ap-propriately addressed by text changes, hence there is no Discussion with Reviewers. 888 

ZnSe Heteroepitaxial Growth on Si (100) and GaAs (100)

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1965&amp;context=microscopy

ZnSe Heteroepitaxial Growth on Si (100) and GaAs (100)

Abstract

Similar works

Full text

Available Versions

DigitalCommons@USU