Using predeposited thin amorphous Si layers, less than 40 Å thick, before chemical vapor deposition (CVD), Si (100) films of high quality were grown successfully on sapphire substrates. This growth method consists of two processes: (1) a sapphire surface is covered in the begging with a amorphous Si layer and (2) Si CVD is carried out on the substrate covered with the amorphous layer. The most remarkable feature of this method is that films with a smooth surface and a high crystalline quality grow even at a slow growth rate, less than 0.1 μm/min and a high growth temperature of about 1000℃. The interface region between the film and the substrate has an abrupt concentration gradient of constituent atoms. In order to investigate the growth features and properties of the films, various physical analyses (RHEED, SIMS, AES and XPS) were used, and electrical properties of MOS FETs were measured. A model to understand this growth method is proposed.
Al_χGa_<1-χ>N (0≦χ≦0.4) layers with thin AlN buffer layers are grown on sapphire (0001) substrates at a temperature of about 1000℃ by MOVPE. By the double crystal X-ray diffratometry the Al_χGa_<1-χ>N layers are found to composed of many mosaic crystallites with vauious orientations. The variation in the crystallite orientation can be much reduced and the surface morphorogy (smoothness and uniformity) of Al_χGa_<1-χ>N is far improved by using the AlN buffer layer. The reason for such an effect of the AlN buffer layer is discussed in detail by the growth mechanism based on the phenomenological model.
Cubic-SiC was grown on Si substrates by a combination of carbonization and consecutive chemical vapor deposition. Grown layer on the (100) and (111) substrates were single crystalline cubic-SiC. Those on the (110) and (211) were poly-crystalline. This difference was due to the difference in crystallinity of carbonized buffer layers. In order to explain the origin of such a result the initial stage of carbonization and atomic arrangements around the interface between Si and SiC were discussed. Grown layers on Si (100) show good crystallinity and the flattest surface among grown layers on these 4 kinds of substrates. However, texture-like morphology was observed, which originated from antiphase domains (APD). Off orientation towards (011) was found to be effective to eliminate APD, which was clarified by the growth on a spherically polished Si (100) substrate. The origin and elimination mechanism of APD were also discussed.
Institute of Materials Science, University of Tsukuba / Institute of Materials Science, University of Tsukuba / Institute of Materials Science, University of Tsukuba / National Institute for Research in Inorganic Materials / National Institute for Research in Inorganic Materials
Direct growth of GaAS layers on Si substrates and the applications to devices are reported. Instead of the large lattice mismatch of 4% between these materials and the polar on nonpolar problem, single domain GaAs layers with a mirror-like surface were grown on (100)-oriented Si substrates by heat treatment at high temperatures and a subsequent two-step growth sequence at low temperatures and then at the conventional growth temperature. RHEED and cross sectional TEM observation showed that the atoms in the first layer rearranged themselves when the wafer was reheated to the conventional growth temperature and most of the dislocations due to the lattice mismatch were confined near the GaAs/Si interface.
GaAs is grown on Si substrate with strained superlattice intermediate layers. Defects, deep levels and stress of the grown GaAs layers on Si are characterized. The use of straind layer superlattices would be effective to obtain other III-V compound semiconductors on Si substrates.
Thermal cyclic growth (TCG) has been used to reduce the dislocation density of GaAs epitaxial layers grown on Si substrates by MOCVD. To evaluate the crystalline quality, we have used etch pit density (EPD) by molten KOH. To confirm the correspondence between the EPD and the dislocation density, we have also employed a transmission electron microscope (TEM) . The degree of the reduction depends on the cycle number N and the temperature difference between the growth temperature T_G and the lowest temperature T_L of the thermal cycles. EPD study reveals a maximum reduction of the dislocation density from 2×10^8 cm^-2 to 1×10^7 cm^-2 for N= 10 and TG = 700℃, T_L = 100℃. TEM study reveals that most threading dislocations in the GaAs grown by the TCG technique are confined on the (111) and (100) planes.
Anti-phase disorder, which is well-known problem in the growth of polar GaAs on nonpolar substrate, is completely suppressed using slightly inclined (100) plane toward , in contrast to the case of exactly oriented (001) plane and inclined (100) plane toward . It is also found that the  orientation of GaAs are always aligned to the inclined direction. Phase locking step model is proposed to understand the elimination of the anti-phase disorder, where the particular atoms with one dangling bond appear at the surface step and they preferentially bond with Ga atoms. Optical and electrical properties of GaAs/Ge layer without the anti-phase disorder are comparable to those of the homoepitaxial layer on GaAs.
The growth of InP films on Si substrates have been studied using metalorganic chemical vapor deposition (MOCVD) technique. A high PH_3/TEI molar ratio (≧150) introduced into the MOCVD reactor is needed to grow In-droplet-free and uniform InP films on Si. An antiphase domain-free (single domain) InP film is obtained on a Si (100) substrate by optimizing substrate preheating temperature. The two-step growth is effective to improve surface morphology of grown films, but is not essential for the single-domain film growth. Defects of 〜1×10^7cm^-2 are revealed in the film by the chemical and the electrochemical etching methods. From the photoluminescence peak energy shift, residual tensile stress in the InP film is estimated to be 〜1×10^9 dyn/cm^2, which is considerably small compared with that in a GaAs film directly grown on Si.