High Quality GaAs on Si by Selective Area Epitaxy
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HIGH QUALITY GaAs ON Si BY SELECTIVE AREA EPITAXY N.H. KARAM,* V. HAVEN,* S.M. VERNON,* N. EL-MASRY,** M. LINGUNIS,*** and N. HAEGEL,*** * Spire Corporation, Patriots Park, Bedford, MA 01730; * North Carolina State University, Raleigh, NC; *** University of California, Los Angeles, CA.
ABSTRACT Selective area Epitaxy (SE) of high quality GaAs on Si films has been achieved using conventional MOCVD and Atomic Layer Epitaxy (ALE) nucleation techniques. Epitaxial GaAs films were deposited inside windows etch patterned in the oxide coated Si wafers. SE was found to eliminate wafer warpage, reduce film cracking and reduce the tensile stresses for islands less than 200 jm/side. Complete stress relief has been achieved in 10 pm/side islands after oxide removal. Defect reduction techniques have been employed resulting in two orders of magnitude reduction in the dislocation density and excellent surface morphologies. This paper addresses the potential of SE, by the above techniques in improving the quality of the GaAs on Si films.
INTRODUCTION The continuing interest in the heteroepitaxy of GaAs on Si is due in part to the potential for the monolithic integration of the GaAs based optical and high speed devices with the advanced Si based technology [1-4]. The two main issues that preclude the full utilization of the GaAs on Si technology are the high dislocation density resulting from the GaAs/ Si lattice mismatch (4.1%) and the residual tensile stress in the GaAs films resulting from the thermal expansion coefficient (TEC) mismatch. These two problems drastically deteriorate the performance and life-time of minority carrier devices (e.g. lasers, LEDs); while majority carrier devices are relatively immune [4]. Selective heteroepitaxy of GaAs on Si is particularly of interest since it can potentially minimize the GaAs/Si TEC mismatch effects such as wafer bow and film cracking to tolerable limits [51, and could also lead to a reduction in defect density [7]. We have recently done SE of GaAs on Si by conventional MOCVD and by ALE nucleation techniques in which the selectively deposited films were comparable to state-of-the-art deposition on unpatterned wafers. In the present paper we further report on the advantages of SE by either deposition technique and demonstrate the first complete stress relief in small size features (10 pm/side) after oxide removal. We also report on the effectiveness of Thermal Cycle Growth (TCG) in improving the crystalline perfection of the selectively deposited films.
EXPERIMENTAL The GaAs on Si films were deposited on two-inch diameter, n-type Si wafers oriented 20 off the (100) toward the (110) direction. The wafers were coated with SiO with thicknesses in the range of 0.05-0.6 micrometers, and square windows (i0-1000 pm/side) were photolithographically etch patterned. The GaAs films were deposited either by the conventional two-step technique, at atmospheric pressure [8] or by ALE nucleation described earlier, at reduced pressure (0.1 atm) [5]. Briefly, following a high temperature bake-out, a
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