Double-crystal X-ray Rocking Curve Measurements Research Articles

Structural characteristics of ZnO films grown on (0001) or (11−20) sapphire substrates by atomic layer deposition

The structural characteristics of zinc oxide (ZnO) films deposited on the (0001)- or (11−20)-oriented sapphire substrates were investigated. ZnO films having low temperature ZnO buffer layers were prepared by atomic layer deposition using diethylzinc and nitrous oxide. The ZnO films were analyzed using cross-sectional transmission electron microscopy, high-resolution transmission electron microscopy and x-ray diffractometry. Cross-sectional high-resolution transmission electron microscopic observations showed the presence of extrinsic stacking faults along with Frankel partial dislocations in ZnO near the ZnO/sapphire heterointerface. Based on the results of cross-sectional transmission electron microscopic observations and double-crystal x-ray rocking curve measurements, it was found that buffer-layer annealing treatment tended to reduce the density of threading dislocations in a ZnO film efficiently so that the crystalline quality of the film was greatly improved.

The dependence of the structural properties on the period numbers and the CdTe thicknesses in HgTe/CdTe superlattices

Double-crystal X-ray rocking curve (DCRC) measurements were performed on HgTe/CdTe superlattices grown by molecular beam epitaxy (MBE) in order to investigate the dependence of the structural properties on the superlattice period number and the CdTe layer thickness. The results of the DCRC measurements showed that the full width at half maximum (FWHM) value of the principal peak decreased with increasing superlattice period number. As the CdTe layer thickness approached the HgTe layer thickness, the FWHM value corresponding to the principal peak decreased, and the optical absorption decreased. As the CdTe layer thickness changed, the detectable range of the HgTe/CdTe superlattice related to the value of the cut-off wavelength varied. These results indicate that HgTe/CdTe superlattices with various superlattice periods and CdTe layer thicknesses hold promise for potential applications in infrared photodetectors operating in a wavelength region between 4.3 and 12.5 μm.

Interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04 Te (211)B substrates by molecular beam epitaxy

Double-crystal x-ray rocking curve (DCRC) and secondary-ion mass-spectroscopy (SIMS) measurements have been performed to investigate the effect of rapid thermal annealing on the interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04Te (211)B substrates by molecular beam epitaxy. The sharp satellite peaks of the DCRC measurements on a 100-period HgTe/CdTe (100A/100A) superlattice show a periodic arrangement of the superlattice with high-quality interfaces. The negative direction of the entropy change obtained from the diffusion coefficients as a function of the reciprocal of the temperature after RTA indicates that the Hg diffusion for the annealed HgTe/CdTe superlattice is caused by an interstitial mechanism. The Cd and the Hg concentration profiles near the annealed HgTe/CdTe superlattice interfaces, as measured by SIMS, show a nonlinear behavior for Hg, originating from the interstitial diffusion mechanism of the Hg composition. These results indicate that a nonlinear interdiffusion behavior is dominant for HgTe/CdTe superlattices annealed at 190°C and that the rectangular shape of HgTe/CdTe superlattices may change to a parabolic shape because of the intermixing of Hg and Cd due to the thermal treatment.

Undoped and doped GaN thin films deposited on high-temperature monocrystalline AlN buffer layers on vicinal and on-axis α(6H)–SiC(0001) substrates via organometallic vapor phase epitaxy

Monocrystalline GaN(0001) thin films have been grown at 950 °C on high-temperature, ≈ 100 nm thick, monocrystalline AlN(0001) buffer layers predeposited at 1100 °C on α(6H)−SiC(0001)Si substrates via OMVPE in a cold-wall, vertical, pancake-style reactor. These films were free of low-angle grain boundaries and the associated oriented domain microstructure. The PL spectra of the GaN films deposited on both vicinal and on-axis substrates revealed strong bound excitonic emission with a FWHM value of 4 meV. The near band-edge emission from films on the vicinal substrates was shifted slightly to a lower energy, indicative of films containing residual tensile stresses. A peak attributed to free excitonic emission was also clearly observed in the on-axis spectrum. Undoped films were too resistive for accurate Hall-effect measurements. Controlled n-type, Si-doping in GaN was achieved for net carrier concentrations ranging from approximately 1 × 1017 cm−3 to 1 × 1020 cm−3. Mg-doped, p-type GaN was achieved with nA−nD ≈ 3 × 1017 cm−3, ρ ≈ 7 Ω · cm, and μ ≈ 3 cm2/V · s. Double-crystal x-ray rocking curve measurements for simultaneously deposited 1.4 μm GaN films revealed FWHM values of 58 and 151 arcsec for deposition on on-axis and off-axis 6H−SiC(0001)Si substrates, respectively. The corresponding FWHM values for the AlN buffer layers were approximately 200 and 400 arcsec, respectively.

Molecular beam epitaxy growth and properties of GaN films on GaN/SiC substrates

Two types of nitrogen plasma sources, an electron cyclotron resonance (ECR) plasma source and a radio frequency (rf) plasma source, were used for the growth of GaN by molecular beam epitaxy (MBE). GaN film quality was correlated with the optical emission characteristics of each type of nitrogen plasma source employed. The best quality GaN films were those grown using the rf nitrogen plasma source. This source was found to emit a much larger fraction of atomic nitrogen and 1st-positive series excited molecular nitrogen in contrast to the ECR plasma source which mainly produced 2nd-positive series excited molecular nitrogen and nitrogen molecular ions when operated under the same conditions. The benefit of homoepitaxial growth of GaN, using metalorganic vapor phase epitaxy grown GaN layers on basal plane 6H-SiC, was seen by the observation of surface reconstructions before, during, and after GaN film growth by MBE. In addition, the MBE-grown GaN films exhibited remarkably intense photoluminescence dominated by a sharp band-edge peak at 3.409 eV having a full-width at half-maximum (FWHM) of 29.7 meV at room temperature. At lower temperatures, splitting of the near-edge excition peaks was observed. Double-crystal x-ray rocking curve measurements of selected MBE-grown GaN films yielded (0002) diffraction peaks having FWHMs as narrow as 156 arcsec.

Growth via Mocvd and Characterization Of GaN and AlxGa1−xN(0001) Alloys for Optoelectronic and Microelectronic Device Applications

ABSTRACTMonocrystalline GaN(0001) thin films have been grown at 950°C on high-temperature, 100 nm thick, monocrystalline AIN(0001) buffer layers previously deposited at 1100°C on α(6H)-SiC(0001)si substrates via MOCVD in a cold-wall, vertical, pancake-style reactor. AlxGa1−xN films (0≤x≤1) were grown directly on the same SiC surface at 1100°C. Abrupt heterojunctions among the alloy composition were demonstrated. All films possessed a smooth surface morphology and were free of low-angle grain boundaries and associated oriented domain microstructures. Double-crystal x-ray rocking curve measurements for the GaN(0004) reflection for simultaneously deposited 1.4 μm films revealed FWHM values of 58 and 151 arcsec for materials grown on on-axis and off-axis material, respectively. The corresponding values for the AIN(0004) buffer layers were ≈ 200 and ≈400 arc sec, respectively. A similar relationship was found for the alloys for 0≤x≤0.2. The PL spectra of the GaN films deposited on both vicinal and on-axis substrates revealed strong bound exciton emission with a FWHM value of 4 meV. The spectra of these films on the vicinal substrates were shifted to a lower energy, indicative of films containing residual tensile stresses. A peak believed to be associated with free excitonic emission was also observed in each on-axis spectrum. Rutherford backscattering, Auger depth profiling and energy dispersive analysis were used to determine the AIN/GaN ratios in the alloys. Cathodoluminescence of solutions with x<0.5 exhibited strong near band edge emission with a FWHM as low as 31 meV. The band gaps were determined via spectral ellipsometry. Undoped GaN and A1xGa1−xN films were too resistive for accurate Hall-effect measurements. Controlled n-type Si-doping in GaN and AlxGa1−xN (for x≤0.4) was achieved for net carrier concentrations ranging from approximately 2×1017 cm−3 to 2×1019 (AlxGa1−xN) or to l × 1020 (GaN) cm−3. Mg-doped, p-type GaN was achieved with nA−nD = 3 × 1017 cm−3, p ≈ 7 Ω cm and μ ≈ 3 cm2/V·s.

InxGa(1−x)N/InyGa(1−y)N superlattices grown on GaN films

High-quality In0.22Ga0.78N/In0.06Ga0.94N superlattices were grown on GaN films with periods of 60 and 200 Å by the two-flow metalorganic chemical-vapor deposition method. The double-crystal x-ray rocking curve measurements showed satellite peaks which indicated the existence of the In0.22Ga0.78N/In0.06Ga0.94N superlattices. The quantum effects were observed through room-temperature photoluminescence (PL) measurements. These PL spectra were compared to theoretical solutions for the In0.22Ga0.78N/In0.06Ga0.94N superlattices.

Accurate determination of misfit strain, layer thickness, and critical layer thickness in ultrathin buried strained InGaAs/GaAs layer by x-ray diffraction

We have analyzed data obtained from double-crystal x-ray rocking curve measurements to determine the lattice constants, strain relaxation, thickness, and critical thickness of a thin InxGa1−xAs layer embedded in GaAs. The use of a very wide x-ray scan angle (∼2.0°) allows the simultaneous determination of buried layer thickness and strain with greater accuracy. The critical thicknesses so obtained for buried InGaAs layers are smaller than that predicted by the energy balance model and larger than that predicted by the force balance model.

Buried Silicide Synthesis and Strain in Cobalt-Implanted Silicon

ABSTRACTSilicon (001) substrates were implaynted with 350 keV Co at room temperature and 450°C with fluence of from l×l017 Co/cm2 to 6×1017 Co/cm . All samples were annealed at 1000°C in order to form the CoSi2 phase Concentration profiles were determined with Rutherford backscattering spectrometry (RBS), and the associated strain profiles were analyzed with double-crystal X-ray rocking curve measurements. Ion channeling was also used to characterize the silicide formation and crystal quality. An implantation of 6×1017 Co/cm2 at 450°C forms a single-crystal CoSi2 layer while lower fluences do not. A continuous, buried CoSi2 single-crystal layer is formed for the 3×1017 Co/cm2 sample implanted at 450°C and annealed at 1000°C. The continous CoSi2 layer is thicker than the critical layer thickness for a fully coherent film, and therefore the layer partially relaxes. A relaxation of 50% of the fully coherent value is observed for this buried silicide system.

Buried Silicide Synthesis and Strain in Cobalt-Implanted Silicon

AbstractSilicon (001) substrates were implanted with 350 keV co at room temperature and 450°C with fluence of from 1x1017 Co/cm2 to 6x10 Co/cm2. All samples were annealed at 1000°C in order to form the CoSi2 phase. Concentration profiles were determined with Rutherford backscattering spectrometry (RBS), and the associated strain profiles were analyzed with double-crystal X-ray rocking curve measurements. Ion channeling was also used to characterize.the suicide formation and crystal quality. An implantation of 6x1017 Co/cm2 at 450°C forms a single-crystal CoSi2 layer while lower fluences do not. A continuous, buried CoSi2 single-crystal layer is formed for the 3x1017 Co/cm2 sample implanted at 450°C and annealed at 1000°C. The continous CoSi2 layer is thicker than the critical layer thickness for a fully coherent film, and therefore the layer partially relaxes. A relaxation of 50% of the fully coherent value is observed for this buried suicide system.

Composition dependence of Au/InxAl1−xAs Schottky barrier heights

The surface barrier heights φbn and room-temperature band gaps Eg of Si-doped InxAl1−xAs layers grown by molecular beam epitaxy on n-type (100) oriented InP substrates have been determined as a function of composition with capacitance versus voltage, internal photoemission, photoluminescence, and double-crystal x-ray rocking curve measurements for 0.45<x<0.55. The results indicate that Eg and φbn are linear functions of x; they also suggest that φbn (0.78)=0 and, for x>0.78, n-type surfaces might be accumulated and p-type surfaces are likely to be inverted.