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.

Thermal annealing behaviour of Ni/Au on n-GaN Schottky contacts

The Schottky behaviour of Ni/Au contact on n-GaN was investigated under various annealing conditions by current-voltage (I-V) measurements. A non-linear fitting method was used to extract the contact parameters from the I-V characteristic curves. Experimental results indicate that high quality Schottky contact with a barrier height and ideality factor of 0.86 +/- 0.02 eV and 1.19 +/- 0.02 eV, respectively, can be obtained under 5 min annealing at 600degreesC in N-2 ambience.

Influence of strain on annealing effects of In(Ga)As quantum dots

Post-growth rapid thermal annealing has been performed with In(Ga)As quantum dots (QDs) at different strain statuses. It is confirmed that the strain-enhanced interdiffusion decreases the inhomogeneous size distribution. The preferential lateral interdiffusion of QDs during annealing was observed. we attribute it to the naturally anisotropic strain distribution in/around the dots and the saturation of strain difference between the base boundary and the top of the dots. There exist strain-enhanced mechanism and vacancy diffusion enhanced mechanism during the annealing. As to which one dominates the QD interdiffusion depends on the thickness of capping layer and the annealing temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Effects of annealing on properties of spin-valve pinned with FeMn alloy

The magnetic properties of spin-valve pinned by FeMn layer were investigated after it was annealed at different temperatures. Its property was dependent on the vacuum annealing temperature. The pinning field could be increased through annealing at a temporature lower than 200degreesC;the pinning field would reduce and other properties be deteriorated as the annealing temperature was higher than 200degreesC; the pinning effect lost and giantmagnetic resistance disappeared at 300degreesC. Based on the results of AES analysis it was concluded that the diffusion in spin-valve multilayer was along grain boundary.

Deep levels in semi-insulating InP obtained by annealing under iron phosphide ambiance

Deep levels in semi-insulating (SI) InP obtained by annealing in iron phosphide (IP) ambiance have been characterized by optical transient current spectroscopy (OTCS). Compared with the OTCS result of the SI InP prepared by annealing in pure phosphorus (PP) ambiance, the IP SI InP presents only two traps with activation energies of 0.20 and 0.63 eV, respectively. The results suggest that the diffusion of Fe-atoms suppresses the formation of a few defects in the IP SI InP. The nature of deep levels in the IP and PP SI InP has been discussed on the basis of these results. The relation between material property and defects in those SI InP has also been revealed. (C) 2002 American Institute of Physics.

Effect of rapid thermal annealing and hydrogen plasma treatment on the microstructure and light-emission of silicon-rich oxide film

Silicon-rich silicon oxide (SRSO) films are prepared by plasma-enhanced chemical vapor deposition method at the substrate temperature of 200degreesC. The effect of rapid thermal annealing and hydrogen plasma treatment on tire microstructure and light-emission of SRSO films are investigated in detail using micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectra. It is found that the phase-separation degree of the films decreases with increasing annealing temperature from 300 to 600degreesC, while it increases with increasing annealing temperature from 600 to 900degreesC. The light-emission of the films are enhanced with increasing annealing temperature up to 500degreesC, while it is rapidly reduced when the annealing temperature exceeds 600degreesC. The peak position of the PL spectrum blueshifts by annealing at the temperature of 300degreesC, then it red-shifts with further raising annealing temperature. The following hydrogen plasma treatment results in a disproportionate increase of the PL intensity and a blueshift or redshift of the peak positions, depending on the pristine annealing temperature. It is thought that the size of amorphous silicon clusters, surface structure of the clusters and the distribution of hydrogen in the films can be changed during the annealing procedure. The results indicate that not only cluster size but also surface state of the clusters plays an important role in the determination of electronic structure of the amorphous silicon cluster and recombination process of light-generated carriers.

Photoluminescence assessment of undoped semi-insulating InP wafers obtained by annealing in iron phosphide vapour

We have investigated the photoluminescence mapping characteristics of semi-insulating (SI) InP wafers obtained by annealing in iron phosphide ambience (FeP2-annealed). Compared with as-grown Fe-doped and undoped SI InP wafers prepared by annealing in pure phosphorus vapour (P-annealed), the FeP2-annealed ST InP wafer has been found to exhibit a better photoluminescence uniformity. Radial Hall measurements also show that there is a better resistivity uniformity on the FeP2-annealed Sl InP wafer. When comparing the distribution of deep levels between the annealed wafers measured by optical transient Current spectroscopy, we find that the incorporation of iron atoms into the Sl InP Suppresses the formation of a few defects. The correlation observed in this study implies that annealing in iron phosphorus ambience makes Fe atoms diffuse uniformly and occupy the indium site in the Sl InP lattice. As it stands, we believe that annealing undoped conductive InP in iron phosphide vapour is an effective means to obtain semi-insulating InP wafers with superior uniformity.

Effect of rapid thermal annealing on electron emission and DX centers in strained InGaAs/GaAs single quantum well laser diodes

Thermal processing of strained In0.2Ga0.8As/GaAs graded-index separate confinement heterostructure single quantum well laser diodes grown by molecular beam epitaxy is investigated. It is found that rapid thermal annealing can improve the 77K photoluminescence efficiency and electron emission from the active layer, due to the removal of nonradiative centers from the InGaAs/GaAs interface. Because of the interdiffusion of Al and Ga atoms, rapid thermal annealing increases simultaneously the density of DX centers in the AlGaAs graded layer. The current stressing experiments of postgrowth and annealed laser diodes are indicative of a corresponding increase in the concentration of DX centers, suggesting that DX centers may be responsible for the degradation of laser diode performance.

Rapid thermal annealing effects on step-graded InAlAs buffer layer and In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistor structures on GaAs substrates

A step-graded InAlAs buffer layer and an In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistor (MM-HEMT) structures were grown by molecular beam epitaxy on GaAs (001) substrates, and rapid thermal annealing was performed on them in the temperature range 500-800 degreesC for 30 s. The as-grown and annealed samples were investigated with Hall measurements, and 77 K photoluminescence. After rapid thermal annealing, the resistivities of step-graded InAlAs buffer layer structures became high. This can avoid leaky characteristics and parasitic capacitance for MM-HEMT devices. The highest sheet carrier density n(s) and mobility mu for MM-HEMT structures were achieved by annealing at 600 and 650degreesC, respectively. The relative intensities of the transitions between the second electron subband to the first heavy-hole subband and the first electron subband to the first heavy-hole subband in the MM-HEMT InGaAs well layer were compared under different annealing temperatures. (C) 2002 American Institute of Physics.

The microstructure and its high-temperature annealing behaviours of a-Si : O : H film

The microstructure and its annealing behaviours of a-Si:O:H film prepared by PECVD are investigated in detail using micro-Raman spectroscopy, X-ray photoelectron spectroscopy and Infrared absorption spectroscopy. The results indicate that the as-deposited a-Si:O:H film is structural inhomogeneous, with Si-riched phases surrounded by O-riched phases. The Si-riched phases are found to be nonhydrogenated amorphous silicon (a-Si) clusters, and the O-riched phases SiOx:H (x approximate to 1. 35) are formed by random bonding of Si, O and H atoms. By high-temperature annealing at 1150 degreesC, the SiOx:H (x approximate to 1.35) matrix is shown to be transformed into SiO2 and SiOx ( x approximate to 0.64), during which all of the hydrogen atoms in the film escape and some of silicon atoms are separated from the SiOx:H ( x approximate to 1.35) matrix; The separated silicon atoms are found to be participated in the nucleation and growth processes of solid-phase crystallization of the a-Si clusters, nano-crystalline silicon (ne-Si) is then formed. The microstructure of the annealed film is thereby described with a multi-shell model, in which the ne-Si clusters are embedded in SiOx (x = 0.64) and SiO2. The former is located at the boundaries of the nc-Si clusters, with a thickness comparable with the scale of nc-Si clusters, and forms the transition oxide layer between the ne-Si and the SiO2 matrix.

Effects of annealing time and Si cap layer thickness on the Si/SiGe/Si heterostructures thermal stability

The effects of annealing time and Si cap layer thickness: on the thermal stability of the Si/SiGe/Si heterostructures deposited by disilane and solid-Ge molecule beam epitaxy were investigated. It is found that in the same strain state of the SiGe layers the annealing time decreases with increasing Si cap layer thickness. This effect is analyzed by a force-balance theory and an equation has been obtained to characterize the relation between the annealing time and the Si cap layer thickness. (C) 2001 Elsevier Science B.V. All rights reserved.

Effects of rapid thermal annealing and SiO2 encapsulation on GaNAs/GaAs single quantum wells grown by plasma-assisted molecular-beam epitaxy

Effects of rapid thermal annealing and SiO2 encapsulation on GaNAs/GaAs single quantum wells grown by plasma-assisted molecular-beam epitaxy were studied. Photoluminescence measurements on a series of samples with different well widths and N compositions were used to evaluate the effects. The intermixing of GaNAs and GaAs layers was clearly enhanced by the presence of a SiO2-cap layer. However, it was strongly dependent on the N composition. After annealing at 900 degreesC for 30 s, a blueshift up to 62 meV was observed for the SiO2-capped region of the sample with N composition of 1.5%, whereas only a small blueshift of 26 meV was exhibited for the bare region. For the sample with the N composition of 3.1%, nearly identical photoluminescence peak energy shift for both the SiO2-capped region and the bare region was observed. It is suggested that the enhanced intermixing is mainly dominated by SiO2-capped layer induced defects-assisted diffusion for the sample with smaller N composition, while with increasing N composition, the diffusion assisted by interior defects become predominant. (C) 2001 American Institute of Physics.

Annealing-induced evolution of defects in low-temperature-grown GaAs-related materials

Infrared absorption spectroscopy, optical transient current spectroscopy (OTCS), and photoluminescence (PL) spectroscopy are used to investigate the annealing induced evolution of defects in low-temperature (LT)-grown GaAs-related materials. Two LT samples of bulk GaAs (sample A) and GaAs/AlxGa1-xAs multiple-quantum-well. (MQW) structure (sample B) were grown at 220 and 320 degreesC on (001) GaAs substrates, respectively. A strong defect-related absorption band has been observed in both as-grown samples A and B. It becomes weaker in samples annealed at temperatures above 600 degreesC. In sample A, annealed in the range of 600-800 degreesC, a large negative decay signal of the optical transient current (OTC) is observed in a certain range of temperature, which distorts deep-level spectra measured by OTCS, making it difficult to identify any deep levels. At annealing temperatures of 600 and 700 degreesC, both As-Ga antisite and small As cluster-related deep levels are identified in sample B. It is found that compared to the As cluster, the As-Ga antisite has a larger activation energy and carrier capture rate. At an annealing temperature of 800 degreesC, the large negative decay signal of the OTC is also observed in sample B. It is argued that this negative decay signal of the OTC is related to large arsenic clusters. For sample B, transient PL spectra have also been measured to study the influence of the, defect evolution on optical properties of LT GaAs/AlxGa1-xAs MQW structures. Our results clearly identify a defect evolution from AS(Ga) antisites to arsenic clusters after annealing.

In situ annealing treatment and In-doping of GaN epilayers grown by MOVPE

The effects of in situ annealing treatment in the initial growth stage and In-doping during growth of the GaN on the material properties were investigated. GaN was grown by LP-MOVPE. In situ annealing reduced the full-width at half-maximum (FWHM) of X-ray rocking curves and reduced etch pit density of GaN films. It improved the optical properties of the epilayer. Undoped and In-doped GaN films of initial growth stage were investigated. It was found that morphology and optical properties were improved in In-doped samples. (C) 2000 Elsevier Science B.V. All rights reserved.

Light and annealing induced changes in Si-H bonds in undoped a-Si : H

Light and annealing induced changes in Si-H bonds in undoped a-Si:H have been investigated by a differential infrared spectroscopy method. The light-induced changes in Si-H bonds are not monotonic, quite different from the usual Staebler-Wronski effect in electronic properties, and involve more complicated physics. The magnitude of the light-induced changes in Si-H bonds is proportional to the hydrogen content in the film. There may exist more than one microscopic process which determine the light-induced changes in Si-H bonds. Almost the whole a-Si:H network is affected when a-Si:H is subjected to Light-soaking or to annealing. The light-induced changes in Si-H bonds may be an independent light-induced phenomenon or an auxiliary process of the metastable SWE defect creation. (C) 2000 Elsevier Science Ltd. All rights reserved.