Epitaxial Growth of Strained Ge Films on GaAs(001) B. Salazar-Herna Ândez a , M.A. Vidal a,1 , H. Navarro-Contreras a, * , C. Va Âzquez-Lo Âpez b a Instituto de Investigacio Ân en Comunicacio Ân Optica, Universidad Auto Ânoma de San Luis Potosõ Â, S.L.P., Alvaro Obrego Ân 64, San Luis Potosõ Â, S.L.P., Mexico 78000 b Dpto. de Fõ Âsica, Centro de Investigacio Ân y Estudios Avanzados del IPN, Apdo. Postal 14-740, 07000 Me Âxico, D.F., Mexico. Received 19 November 1998; received in revised form 23 April 1999; accepted 23 April 1999 Abstract Ge ®lms were grown epitaxially as well as pseudomorphically on GaAs(001) substrates at different temperatures using high-vacuum magnetron sputtering. The crystal quality of the resultant layers was examined by high-resolution X-ray diffraction (HRXRD). The rocking curves of Ge layer grown at temperatures greater than 4708C show clear Pendello È sung oscillations, con®rming the high crystalline quality of the Ge layers. The angular position of the Ge diffraction peak is observed shifted from that for a pure Ge layer grown pseudomorphically on GaAs. Calculations from the lattice parameter model are consistent with the supposition of Ge ®lms with high concentrations of As or Ga, as recon®rmed by Hall effect measurements. Atomic Force Microscope (AFM) measurements performed to characterize the Ge surface, indicate that the RMS surface roughness is typically 30 A Ê , but that it can be as low as 3 A Ê for intermediate temperatures, a value that compares favorable with those obtained for molecular beam epitaxially grown material. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Germanium; Epitaxy; Sputtering; X-ray diffraction 1. Introduction Heteroepitaxial ®lms of Ge on GaAs have attracted much interest over the last few years [1±11]. With about 0.1% lattice mismatch, the so formed heterojunction has a wide range of applications. For example, Ge has applications in the ®eld of microelectronics due to its high intrinsic hole mobility and strong absorption in the 1.0±1.5 mm wave- length range [5]. The heterostructure Ge/GaAs is used widely in solar cells [5]. Ge is also a promising material for the waveguides of electro-optic integrated circuits in GaAs based devices utilizing mid-infrared, which includes the important 3±10 mm wavelength region. Pure Ge is trans- parent at these wavelengths, since it has a relatively large index of refraction, n  4:0, enabling it to con®ne light via total internal re¯ection [2,6,7]. The 0.1% lattice mismatch between Ge and GaAs enables the growth of high crystalline quality Ge on GaAs. However, to achieve defect free epitaxy, one must deposit the Ge ®lms at temperatures greater than 4008C [8]. At these temperatures the main problems encountered are the interdiffusion of As, Ga and Ge across the interface and doping of the Ge [9±11] epilayer. Conventionally, heteroepitaxy of Ge on GaAs has been achieved by the deposition from vapor phase Ge atoms onto heated substrates using e-beam techniques [1,2,7,8]. Also heteroepitaxy of Ge has been achieved by chemical vapor deposition [3,10] and molecular beam epitaxy [4,9,11,12]. Growth of single crystalline Ge by sput- tering techniques has been reported since the decade of the 60s [13]. However, to the best of our knowledge, at the present moment high quality growth of Ge on GaAs using magnetron sputtering has been not reported. Recently [14], we reported the growth of (GaAs) 12x (Ge 2 ) x /GaAs multi- layers, where the intentional incorporation de Ga and As to Ge layer has been achieved via sputtering of a GaAs target. In these samples the intentional incorporation of As and Ga into the Ge-rich layers resulted in the existence of linear variations of x en the Ge rich layers. In this letter, we report the pseudomorphic growth of high quality Ge layers on top of GaAs(001) by magnetron sput- tering. We determine the effect of high concentrations of As and Ga diffused into the Ge epilayers by HRXRD and show that modern magnetron sputtering is also a useful technique to grow Ge of high quality. From AFM measurements, we determine the surface roughness to be smaller than 35 A Ê for some Ge layers that show Pendello Èsung oscillations. We Thin Solid Films 352 (1999) 269±272 0040-6090/99/$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S0040-6090(99)00332-6 www.elsevier.nl/locate/tsf * Corresponding author. Tel.: 152-4825-0183; fax: 152-4825-0198. E-mail address: hnavarro@cactus.iico.vaslp.mx (H. Navarro-Contreras) 1 Co-corresponding author. E-mail address: mavidal@catus.iico.v- aslp.mx (M.A. Vidal)