Heteroepitaxial growth and annealing of gamma-Al2O3 thin films on silicon

The gamma-Al2O3 films were grown on Si (100) substrates using the sources of TMA (Al (CH3)(3)) and O-2 by very low-pressure chemical vapor deposition (VLP-CVD). It has been found that the gamma-Al2O3 film has a mirror-like surface and the RMS was about 2.5nm. And the orientation relationship was gamma-Al2O3(100)/Si(100). The thickness uniformity of gamma-Al2O3 films for 2-inch epi-wafer was less than 5%. The X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) results show that the crystalline quality of the film was improved after the film was annealed at 1000degreesC in O-2 atmosphere. The high-frequency C-V and leakage current of Al/gamma-Al2O3/Si capacitor were also measured to verify the annealing effect of the film. The results show that the dielectric constant increased from 4 to 7 and the breakdown voltage for 65-nm-thick gamma-Al2O3 film on silicon increases from 17V to 53V.

Growth mode and strain evolution during InN growth on GaN(0001) by molecular-beam epitaxy

Epitaxial growth of InN on GaN(0001) by plasma-assisted molecular-beam epitaxy is investigated over a range of growth parameters including source flux and substrate temperature. Combining reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM), we establish a relationship between film growth mode and the deposition condition. Both two-dimensional (2D) and three-dimensional (3D) growth modes of the film are observed. For 2D growth, sustained RHEED intensity oscillations are recorded while STM reveals 2D nucleation islands. For 3D growth, less than three oscillation periods are observed indicating the Stranski-Krastanov (SK) growth mode of the film. Simultaneous measurements of (reciprocal) lattice constant by RHEED suggest a gradual relaxation of the strain in film, which commences during the first bilayer (BL) deposition and almost completes after 2-4 BLs. For SK growth, 3D islanding initiates after the strain has mostly been relieved, presumably by dislocations, so the islands are likely strain free. (C) 2002 American Institute of Physics.

Investigation of GaN layer grown on Si(111) substrate using an ultrathin AlN wetting layer

High-quality GaN epilayers were grown on Si (1 1 1) substrate by metalorganic chemical vapor deposition. The growth process was featured by using an ultrathin AlN wetting layer (WL) in combination with a low-temperature (LT) GaN nucleation layer (NL). The full-width at half-maximum (FWHM) of the X-ray rocking curve for the GaN (0 0 0 2) diffraction was 15 arcmin. The dislocation density estimated from TEM investigation was found to be of the order of 10(9)cm(-2). The FWHM of the dominant band edge emission peak of the GaN was measured to be 47 meV by photoluminescence measurement at room temperature. The ultrathin AlN WL was produced by nitridation of the aluminium pre-covered substrate surface. The reflection high-energy electron diffraction showed that the AlN WL was wurtzite and the surface morphology was like the nitridated surface of sapphire by the atomic force microscopy measurement. X-ray photoelectron spectroscopy measurement showed that Si and SixNy at a certain concentration were intermixed in the AlN WL. This study suggests that by employing an appropriate WL combined with a LT NL, high-quality heteroepitaxy is achievable even with large mismatch. (C) 2002 Elsevier Science B.V. All rights reserved.

Carbonization process of Si(100) by ion-beam bombardment

The evolution of carbonization process on Si as a function of ion dose has been carried out by mass-selected ion-beam deposition technique. 3C-SiC layer has been obtained at low ion dose, which has been observed by reflection high energy electron diffraction and X-ray photoelectron spectroscopy (XPS). The chemical states of Si and carbon have also been examined as a function of ion dose by XPS. Carbon enrichment was found regardless of the used ion dose here, which may be due to the high deposition rate. The formation mechanism of SiC has also been discussed based on the subplantation process. The work will also provide further understanding of the ion-bombardment effect. (C) 2001 Published by Elsevier Science B.V.

Quality improvement of GaInNAs/GaAs quantum wells grown by plasma-assisted molecular beam epitaxy

The optimum growth condition of GaInNAs/GaAs quantum wells (QWs) by plasma-assisted molecular beam epitaxy was investigated. High-resolution X-ray diffraction and photoluminescence (PL) measurements showed that ion damage drastically degraded the quality of GaNAs and GaInNAs QWs and that ion removal magnets can effectively remove the excess ion damage. Remarkable improvement of PL intensity and obvious appearance of pendellosung fringes were observed by removing the N ions produced in the plasma cell. When the growth rate increased from 0.73 to 1.2 ML/s, the optimum growth temperature was raised from 460 degreesC to 480 degreesC and PL peak intensity increased two times. Although the N composition decreased with increasing growth rate, degradation of optical properties of GaInNAs QWs was observed when the growth rate was over 0.92 ML/s. Due to low-temperature growth of GaInNAs QWs, a distinctive reflection high-energy electron diffraction pattern was observed only when the GaAs barrier was grown under lower As-4 pressure. The samples with GaAs barriers grown under lower As-4 pressure (V/III ratio about 24) exhibited seven times increase in PL peak intensity compared with those grown under higher As-4 pressure (V/III ratio about 50). (C) 2001 Elsevier Science B,V. All rights reserved.

Growth and photoluminescence of epitaxial CeO2 film on Si (111) substrate

A CeO2 film with a thickness of about 80nm was deposited by a mass-analysed low-energy dual ion beam deposition technique on an Si(111) substrate. Reflection high-energy electron diffraction and x-ray diffraction measurements showed that the film is a single crystal. The tetravalent state of Ce in the film was confirmed by x-ray photoelectron spectroscopy measurements, indicating that stoichiometric CeO2 was formed. Violet/blue light emission (379.5 nm) was observed at room temperature, which may be tentatively explained by charge transitions from the 4f band to the valence band of CeO2.

Self-assembled InAs quantum wires on InP(001)

Self-assembled InAs quantum wires (QWRs) embedded in In0.52Al0.48As, In0.53Ga0.47As, and (In0.52Al0.48As)(n)/(In0.53Ga0.47As)(m)-short-period-lattice matrices on InP(001) were fabricated with molecular beam epitaxy (MBE). These QWR lines are along [110], x 4 direction in the 2 x 4 reconstructed (001) surface as revealed with reflection high-energy electron diffraction (RHEED). Alignment of quantum wires in different layers in the InAs/spacer multilayer structures depends on the composition of spacer layers. (C) 2000 Elsevier Science B.V. All rights reserved.

X-ray double-crystal characterization of the strain relaxation in GaAs/GaNxAs1-x/GaAs(001) sandwiched structures

An X-ray diffraction method, estimating the strain relaxation in an ultrathin layer, has been discussed by using kinematic and dynamical X-ray diffraction (XRD) theory. The characteristic parameter Delta Omega, used as the criterion of the strain relaxation in ultrathin layers, is deduced theoretically. It reveals that Delta Omega should be independent of the layer thickness in a coherently strained layer. By this method, we characterized our ultrathin GaNxAs1-x samples with N contents up to 5%. XRD measurements show that our GaNxAs1-x layers are coherently strained on GaAs even for such a large amount of N. Furthermore, a series of GaNxAs1-x samples with same N contents but different layer thicknesses were also characterized. It was found that the critical thickness (L-c) of GaNAs in the GaAs/GaNAs/GaAs structures determined by XRD measurement was 10 times smaller than the theoretical predictions based on the Matthews and Blakeslee model. This result was also confirmed by in situ observation of reflection high-energy electron diffraction (RHEED) and photoluminescence (PL) measurements. RHEED observation showed that the growth mode of GaNAs layer changed from 2D- to 3D-mode as the layer thickness exceeded L-c. PL measurements showed that the optical properties of GaNAs layers deteriorated rapidly as the layer thickness exceeded L-c. (C) 2000 Elsevier Science B.V. All rights reserved.

Structural and photoluminescence properties of In-0.9(Ga/Al)(0.1)As self-assembled quantum dots on InP substrate

Self-assembled In0.9Ga0.1As, In0.9Al0.1As, and InAs quantum dots (QD) were fabricated in an InAlAs matrix lattice-matched to an InP substrate by molecular beam epitaxy. Preliminary characterizations were performed using transmission electron microscopy, photoluminescence, and reflection high-energy electron diffraction. Experimental results reveal clear differences in QD formation, size distribution, and luminescence between the InAs and In-0.9(Ga/Al)(0.1)As samples, which show the potential of introducing ternary compositions to adjust the structural and optical properties of QDs on an InP substrate. (C) 2000 American Institute of Physics. [S0021-8979(00)10213-0].

Influences of initial buffer layer deposition on electrical and optical properties in cubic GaN grown on GaAs(100) by metalorganic chemical vapor deposition

We present some results on the effect of initial buffer layer on the crystalline quality of Cubic GaN epitaxial layers grown on GaAs(100) substrates by metalorganic chemical vapor deposition. Photoluminescence and Hall measurements were performed to characterize the electrical and optical properties of cubic GaN. The crystalline quality subsequently grown high-temperature (HT) cubic GaN layers strongly depended on thermal effects during the temperature ramping process after low temperature (LT) growth of the buffer layers. Atomic force microscope (AFM) and reflection high-energy electron diffraction (RHEED) were employed to investigate this temperature ramping process. Furthermore, the role of thermal treatment during the temperature ramping process was identified. Using the optimum buffer layer, the full width at half maxim (FWHM) at room temperature photoluminescence 5.6 nm was achieved. To our knowledge, this is the best FWHM value for cubic GaN to date. The background carrier concentration was as low as 3 x 10(13) cm(-3). (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Effect of low-temperature SiGe interlayer on the growth of relaxed SiGe

A low-temperature Si0.8Ge0.2 (LT-Si0.8Ge0.2) interlayer was grown at 500 degrees C to improve the relaxed Si0.8Ge0.2 surface and reduce the dislocation density in it, which was confirmed by the change of reflective high-energy electron diffraction (RHEED) pattern from spotty to streaky and etch pits counts. For the same extent of strain; the threading dislocation density was reduced from 8 x 10(7) cm(-2) in the latter to 2 x 10(6) cm(-2) in the former. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of buffer layer growth conditions on the secondary hexagonal phase content in cubic GaN films on GaAs(001) substrates

In this letter, we investigated the effect of the buffer layer growth conditions on the secondary hexagonal phase content in cubic GaN films on GaAs(0 0 1) substrate. The reflection high-energy electron diffraction (RHEED) pattern of the low-temperature GaN buffer layers shows that both the deposition temperature and time are important in obtaining a smooth surface. Four-circle X-ray double-crystal diffraction (XRDCD) reciprocal space mapping was used to study the hexagonal phase inclusions in the cubic GaN (c-GaN) films grown on the buffer layers. The calculation of the volume contents of the hexagonal phase shows that higher temperature and longer time deposition of the buffer layer is not preferable for growing pure c-GaN film. Under optimized condition, 47 meV FWHM of near band gap emission of the c-GaN film was achieved. (C) 2000 Elsevier Science B.V. All rights reserved.

Growth and characterization of strained superlattices delta-GaNxAs1-x/GaAs by molecular beam epitaxy

A series of superlattices delta-GaNxAs1-x/GaAs were grown by a DC plasma-N-2-assisted molecular beam epitaxy. The evolution of the surface reconstruction during the growth has been studied with the use of in situ reflection high-energy electron diffraction. The superlattices have been characterized by high-resolution X-ray diffraction measurements. Distinct satellite peaks indicate that the superlattices are of good quality. The N compositions in strained GaNxAs1-x monolayers are obtained from the dynamical simulations of the measured X-ray diffraction patterns. The periodicity fluctuations of N composition are obtained from a kinematical method dependent on the broadening of the satellite peaks of the X-ray diffraction. (C) 2000 Elsevier Science B.V. All rights reserved.

Initial stages of GaN/GaAs (100) growth by metalorganic chemical vapor deposition

We have investigated the growth of GaN buffers by metalorganic chemical vapor deposition (MOCVD) on GaAs (100) substrates. Atomic force microscope (AFM) and reflection high-energy electron diffraction (RHEED) were employed to study the dependence of the nucleation on the growth temperature, growth rate, annealing effect, and growth time. A two-step growth sequence must be used to optimize and control the nucleation and the subsequent growth independently. The size and distribution of islands and the thickness of buffer layers have a crucial role on the quality of GaN layers. Based on the experimental results, a model was given to interpret the formation of hexagonal-phase GaN in the cubic-phase GaN layers. Using an optimum buffer layer, the strong near-band emission of cubic GaN with full-width at half maximum (FWHM) value as small as 5.6 nm was observed at room temperature. The background carrier concentration was estimated to be in the range of 10(13) similar to 10(14) cm(-3).

Growth mode and strain relaxation of InAs on InP (111)A grown by molecular beam epitaxy

Growth mode and strain relaxation of molecular-beam-epitaxy grown InAs/InAlAs/InP (111)A system have been investigated using reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence measurements. In direct contrast to the well-studied InAs/GaAs system, our experimental results show that the InAs grown on InAlAs/InP (111)A follows the Stranski-Krastanov mode. Both self-organized InAs quantum dots and relaxed InAs islands are formed depending on the InAs coverage. Intense luminescence signals from both the InAs quantum dots and wetting layer are observed. The luminescence efficiency of (111)A samples is comparable to that of (001) samples, suggesting the feasibility of fabricating quantum dot optoelectronic devices on InP (111)A surfaces. (C) 1999 American Institute of Physics. [S0003-6951(99)01010-4].