High Quality AlN and GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia
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Sergey A. Nikishin, Nikolai N. Faleev, Vladimir G. Antipov, Sebastien Francoeur, Luis Grave de Peralta, George A. Seryogin, Mark Holtz1, Tat’yana I. Prokofyeva1, S. N. G. Chu2, Andrei S. Zubrilov3, Vyacheslav A. Elyukhin3, Irina P. Nikitina3, Andrei Nikolaev3, Yuriy Melnik4, Vladimir Dmitriev4 , and Henryk Temkin Dept of Electrical Engineering, Texas Tech University, Lubbock, TX 79409, U. S. A. 1 Dept of Physics, Texas Tech University, Lubbock, TX 79409, U. S. A. 2 Lucent/Bell Labs, Murray Hill, NJ 07974, U. S. A. 3 Ioffe Physical-Technical Institute, St.Petersburg, 194021, Russia 4 TDI, Inc., Gathersburg, MD 20877, U. S. A. ABSTRACT We describe the growth of high quality AlN and GaN on Si(111) by gas source molecular beam epitaxy (GSMBE) with ammonia (NH3). The initial nucleation (at 11301190K) of an AlN monolayer with full substrate coverage resulted in a very rapid transition to two-dimensional (2D) growth mode of AlN. The rapid transition to the 2D growth mode of AlN is essential for the subsequent growth of high quality GaN, and complete elimination of cracking in thick ( > 2 µm) GaN layers. We show, using Raman scattering (RS) and photoluminescence (PL) measurements, that the tensile stress in the GaN is due to thermal expansion mismatch, is below the ultimate strength of breaking of GaN, and produces a sizable shift in the bandgap. We show that the GSMBE AlN and GaN layers grown on Si can be used as a substrate for subsequent deposition of thick AlN and GaN layers by hydride vapor phase epitaxy (HVPE). INTRODUCTION There have been numerous recent attempts to prepare AlGaN-based heterostructures on Si (111) substrates [1-4]. The achievements of plasma assisted MBE (PAMBE) of AlN and GaN on Si(111) have been summarized in [5, 6]. GSMBE, with direct decomposition of NH3 on the substrate surface,[7] can also be used to grow high quality AlN [8] and GaN [7, 9-11]. In the present paper we describe growth of AlN and GaN by GSMBE with NH3 on Si(111) substrates. We use in situ reflection high-energy electron diffraction (RHEED), low energy electron diffraction (LEED) and ex situ triple-crystal x-ray diffraction (XRD), transmission electron microscopy (TEM), RS, and PL to study structure and optical properties. XRD results from AlN and GaN layers, grown by HVPE on the GSMBE AlN and GaN layers are also reported. EXPERIMENTAL DETAILS AND DISCUSSION All growth experiments were carried out on 2 and 3-in oriented Si (111) substrates prepared by wet chemical etching [12]. The procedure used results in a hydrogen terminated Si surface. Substrates prepared by this process showed the (7×7) surface structure, observed by RHEED, after heating to 920 K for few minutes. The well known
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Si(111) surface reconstruction transition, from (7×7) to (1×1), which occurs at Tt=1100 K [13, 14], provided a convenient temperature calibration point [9]. It is well known that once the growth chamber is used for the growth of nitrides, the residual nitrogen at the temperature range of 1100-1200 K induces formation of Si-N bonds on the s
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