Effect Of Post-growth Annealing Research Articles

β -phase-domain-free α-MnAs thin films on GaAs(001) by postgrowth annealing

Postgrowth annealing effects on a heteroepitaxial MnAs thin film grown on a GaAs(001) substrate have been investigated. The β-MnAs phase domains of an as-grown sample, observed as dark stripes in the surface topography at room temperature, disappear completely after postgrowth annealing. In support of this finding, the paramagnetic contribution to the magnetic hysteresis loop arising from the β-MnAs phase domains is also not observed at 300K. We attribute the origin of these effects to relaxation of the elastic strain in the MnAs thin film.

Effect of annealing ambient flux on InAs islands grown on GaAs(0 0 1) substrates by metal–organic vapor phase epitaxy

Effects of post-growth annealing under dissimilar ambient fluxes on InAs islands grown on GaAs(0 0 1) substrates by low pressure metal–organic vapor phase epitaxy (LP-MOVPE) have been investigated. It is found that InAs islands annealed under different ambient fluxes exhibit different surface morphology evolution. Islands annealed under DMHy flux exhibit dissolving of the 3D island morphology. In contrast, upon annealing under TMSb flux, the 3D island morphology is enhanced with increased island density. The result suggests that we can fine tune the size and density of InAs islands by post-growth annealing under different ambient fluxes and this method is expected to be applicable to the growth of QDs of other material systems. Our findings are discussed in terms of the existence of critical nucleus in heterogeneous growth processes.

High sensitivity Si-based backward diodes for zero-biased square-law detection and the effect of post-growth annealing on performance

High-sensitivity Si-based backward diodes were realized that are monolithically integratable with transistor circuitry. Potential applications include large area focal plane arrays. The Si-based backward diodes exhibit a high zero-biased curvature coefficient, /spl gamma/, of 31 V/sup -1/ and a low zero biased junction capacitance, C/sub j/, of 9 fF/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , all at room temperature. The predicted low frequency voltage sensitivity, /spl beta//sub V/, for a 50 /spl Omega/ source is 3100 V/W. The high sensitivity, low junction capacitance, and Si/SiGe heterojunction bipolar transistor compatibility of the Si-based backward diodes make them very attractive for zero-bias square-law detector applications.

Effects of postgrowth rapid thermal annealing on InAlAs∕InGaAs metamorphic high-electron-mobility transistor grown on a compositionally graded InAlAs∕InGaAlAs buffer

Effects of postgrowth rapid thermal annealing (RTA) on structural and electrical properties of an In0.52Al0.48As∕In0.52Ga0.48As metamorphic high-electron-mobility transistor (MHEMT) structure grown on a GaAs substrate utilizing a compositionally graded InAlAs∕InGaAlAs buffer layer were investigated. High-resolution triple-axis x-ray diffraction, photoluminescence, and van der Pauw–Hall measurements were used for the investigation. While the RTA improved the structural property of the MHEMT, it degraded the channel mobility of the MHEMT due to defect-assisted impurity redistribution.

Effects of doping profile and post-growth annealing on spin injection from Fe into (Al,Ga)As heterostructures

The influence of the Fe∕Ga0.9Al0.1As interface on spin injection into a spin light-emitting diode is studied. Spin injection is found to depend strongly on the interfacial doping profile demonstrating the importance of band bending in the semiconductor near the interface. The effect of post-growth annealing on spin injection from Fe contacts into GaAs-based spin light-emitting diodes is also examined. Post-growth annealing up to 250 °C is found to increase the spin injection efficiency. It is demonstrated that the annealing modifies electronic properties of the Fe∕Ga0.9Al0.1As interface, as evidenced by an increase of the Schottky barrier height.

Effect of growth temperature and post-growth thermal annealing on carrier localization and deep level emissions in GaNAs∕GaAs quantum well structures

We report results from investigation of the optical properties of GaNAs∕GaAs quantum well structures. The structures were grown by molecular-beam epitaxy at different temperatures, and subsequently postgrowth thermal treatments at different temperature were performed. The results show that the carrier localization is smaller in a structure grown at a temperature of 580°C in comparison with a structure grown at 450°C. Both structures also show a broaden deep level emission band. Furthermore, the deep level emission band and the carrier localization effect can be removed by thermal annealing at 650°C in the structure grown at 450°C. The structure quality and radiative recombination efficiency are significantly improved after annealing. However, annealing under the same condition has a negligible effect on the structure grown at 580°C.

1.28μm lasing from stacked InAs∕GaAs quantum dots with low-temperature-grown AlGaAs cladding layer by metalorganic chemical vapor deposition

We report the device characteristics of stacked InAs∕GaAs quantum-dot lasers cladded by Al0.4Ga0.6As layer grown at a low temperature by metalorganic chemical vapor deposition. A blueshift in emission energy by the effect of postgrowth annealing can be suppressed when the annealing temperature is below 570°C. We achieved the 1.28μm continuous-wave lasing at room temperature of five layer stacked InAs∕GaAs quantum dots embedded in In0.13Ga0.87As strain-reducing layer whose p-cladding layer is grown at 560°C. From the experiments and calculations of the gain spectra of fabricated quantum-dot lasers, the observed lasing originates from the first excited state of stacked InAs quantum dots.

Improvement of crystal quality of GaInNAs films grown by atomic hydrogen-assisted RF-MBE

The effect of post-growth annealing and atomic H irradiation in molecular beam epitaxy (MBE) of Ga(In)NAs on vacancy-type defects was studied by positron annihilation technique. We observed a reduction of vacancy-type defects after post-growth anneal at 600 °C for 5 min in a flowing N 2 ambient. However, irradiation of atomic H during growth showed no apparent effect on vacancy-type defects. The role of atomic H irradiation in MBE is known to enhance two-dimensional growth mode, which results in overall improvement of material quality. However, we found that supply of excessive amounts of atomic H would result in degradation of GaInNAs films. Under optimized conditions of ∼1% cracking ratio and 0.6 sccm H 2 flow rate, a surface roughness of 0.27 nm or ∼1 monolayer (ML) was successfully obtained.

Low-temperature silicon epitaxy on hydrogen-terminated Si(001) surfaces

Si deposition on H terminated $\mathrm{Si}(001)\text{\ensuremath{-}}2\ifmmode\times\else\texttimes\fi{}1$ surfaces at temperatures $300--530\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is studied by scanning tunneling microscopy. Hydrogen apparently hinders Si adatom diffusion and enhances surface roughening. The post-growth annealing effect is analyzed. Hydrogen is shown to remain on the growth front up to at least $10\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$. Si deposition onto the $\mathrm{H}∕\mathrm{Si}(001)\text{\ensuremath{-}}3\ifmmode\times\else\texttimes\fi{}1$ surface at $530\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ suggests that dihydride units further suppress Si adatom diffusion and increase surface roughness.

In As ∕ Ga As self-assembled quantum-dot lasers grown by metalorganic chemical vapor deposition—Effects of postgrowth annealing on stacked InAs quantum dots

We investigated the effects of postgrowth annealing on stacked InAs∕GaAs quantum dots. The blueshift in emission energy by postgrowth annealing depends on the temperature of postgrowth annealing and the growth conditions of stacked InAs quantum dots, such as a spacer thickness or a stacking number. We can control the peak wavelength of stacked InAs quantum dots by changing the temperature of postgrowth annealing and the growth conditions of stacked InAs quantum dots. We achieved continuous-wave lasing with a threshold current of 16.4mA at the wavelength of 1.245μm from five layer vertically aligned InAs quantum dots whose upper cladding layer was grown at 600°C.

Annealing in GaInNAs system

The effect of post-growth thermal annealing on crystallinity and bandgap in GaInNAssystems is systematically investigated. Annealing greatly improves the crystallinity ofGaInNAs and also blue shifts the bandgap. This improved crystallinity is due to theelimination of non-radiative centres, and is not directly related to the blue shift in thebandgap. The blue shift may be closely related to the red shift in the bandgap seen when Nis added to GaInNAs; if so, this would provide a clue to the reasons for the red shift in thebandgap of III–N–V alloys. The unexpected behaviour of the bandgap in GaInNAs isinvestigated by examining the bonds through optical phonons. We have found that thebandgap varies with the strength or length of the GaN bonds in GaInNAs. Annealingchanges atomic positions in a unit cell of GaInNAs and thus blue shifts its bandgap.

Effect of postgrowth annealing on the morphology and magnetic properties of MnAs thin films grown on GaAs(001) substrates

We have investigated the effect of postgrowth annealing on the surface morphology and magnetic properties of monocrystalline MnAs thin films epitaxially grown on GaAs(001) substrates by molecular beam epitaxy. After the growth of MnAs, the postgrowth annealing was carried out in the temperature range between 330 and 400 °C, with keeping the MnAs surface exposed to the As flux. The surface morphology and crystallinity of MnAs thin films were drastically improved by optimizing the annealing temperature. The magnetic properties, such as saturation magnetization, coercivity, and the magnetoresistance characteristics of the MnAs films were sensitive to their crystallinity, which was determined by the annealing temperature.

Study of post-growth annealing and Ga coverage effects in low-density GaAs/AlGaAs quantum dots grown by modified droplet epitaxy

Abstract We present a detailed analysis of the Ga coverage and of the post-growth annealing effects on the optical properties of very-low-density self-assembled GaAs/AlGaAs quantum dots grown by modified droplet epitaxy. Through theoretical calculation of the QD electronic states, including thermally activated Al–Ga interdiffusion processes, we were able to relate our spectroscopic observations to QD structural properties.

Study of post-growth annealing and Ga coverage effects in low-density GaAs/AlGaAs quantum dots grown by modified droplet epitaxy

We present a detailed analysis of the Ga coverage and of the post-growth annealing effects on the optical properties of very-low-density self-assembled GaAs/AlGaAs quantum dots grown by modified droplet epitaxy . Through theoretical calculation of the QD electronic states, including thermally activated Al–Ga interdiffusion processes, we were able to relate our spectroscopic observations to QD structural properties.

Tuning of the electronic properties of self-assembled InAs/InP(001) quantum dots by rapid thermal annealing

We have investigated the effect of post-growth rapid thermal annealing on the low-temperature photoluminescence (PL) spectra of self-assembled InAs quantum dots (QDs) grown in InP(001) by chemical-beam epitaxy using both conventional and modified capping procedures. As-grown samples are characterized by a broad emission peak centered near 800–900 meV corresponding to distinct QD families of different sizes with no observable wetting-layer emission. Rapid thermal anneals were performed at 650 to 800 °C for 210 s, resulting in blueshifts of up to 120 meV due to intermixing. While the PL emission energies of the various QD families shift at similar rates upon annealing, the peak widths remain approximately constant. Finally, we show that the growth of a low-temperature InP cap layer containing a large number of point defects significantly enhances interdiffusion and results in PL blueshifts in excess of 300 meV.

Post-growth annealing effects in compensated μc-Si:H samples

In this work we study the effect of low temperature annealing on the transport properties of μc-Si:H. We performed post-growth annealing on a series of micro-doped μc-Si:H samples having different degrees of compensation, extending from n-type to p-type character. The samples were isothermally annealed at 423 K, 10 K below the deposition temperature. An increase of up to four orders of magnitude was observed in the dark conductivity ( σ dk) for the low temperature region. Simultaneously, the activation energy ( E a) of the dark conductivity changes depending on the doping level and the annealing time. Absorption coefficient and density of states measurements have been done for different annealing stages by using the constant photocurrent method and the modulated photocurrent technique, respectively. The density of defects in the midgap region increases during the annealing while the band tails remain unaffected. The σ dk and E a behavior can be interpreted in terms of a shift of the Fermi level towards the valence band. A model based in doping activation is proposed in order to explain this behavior.

Thermal stability of sputtered zirconium oxide films

In this work, the effect of post-growth annealing on the structural and optical properties of sputtered zirconium oxide films has been investigated. The temperature dependence of structure, density, and optical constants has been systematically studied by X-ray diffraction, X-ray reflectometry, atomic force microscopy (AFM) and optical spectroscopy. X-ray diffraction studies show no variation in the crystalline phase upon annealing except grain growth. X-ray reflectivity measurements determine a density increase of approximately 11% and a simultaneous thickness reduction of 10% upon annealing. The surface roughness of the films increases upon annealing as determined by XRR and confirmed by AFM measurements. Optical spectroscopy measurements confirm that the refractive index n of the films decreases with increasing annealing temperature. At the same time the optical band gap E g of the films increases from 4.58 to 4.97 eV annealing at 900°C. The surprising decrease of refractive index upon annealing is attributed to both the intermixing of Si with ZrO 2 and the increasing surface roughness of the films.

Progress in the Growth and Characterization of Ge Quantum Dots and Islands

ABSTRACTWe review progress in the growth of Si1-xGex islands and Ge dots on (001) Si. We discuss the evolution of the island morphology with Si1-xGex coverage, and the effect of growth parameters or post-growth annealing on the shape of the islands and dots. We outline some of the structural, and optical properties of Si1-xGex islands and review recent progress in the determination of their composition and strain distribution. We discuss various approaches currently being investigated to engineer Si1-xGex quantum dots and in particular control their size, density and spatial distribution. For example, we show how C pre-deposition on Si (001) can influence nucleation and growth of Ge islands.

The effect of postgrowth annealing on the structure and optical properties of multilayer Ge/Si heterostructures

The effect of the postgrowth laser and thermal annealing on the structure and optical properties of multilayer heterostructures comprising quantum dots of germanium in a silicon matrix has been studied by photoluminescence (PL) and transmission electron microscopy (TEM). The PL spectra of annealed samples reveal a decrease of emission from the quantum dots and display a new emission band as compared to the initial spectra. The TEM measurements show that this effect is related to smearing of the Ge-Si interface and to the appearance of a regular rectangular network of dislocations on the surface of the annealed structure.

Effects of Annealing on the Properties of Molecular Thin Film Heterostructures

The effects of post‐growth annealing on the structure, morphology, and spectroscopic properties of molecular double‐layer heterostructures containing perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA) and metal‐free phthalocyanine (H2Pc) have been investigated. The templated structure adopted by H2Pc on PTCDA protects the underlying PTCDA layer from sublimation, unless the H2Pc thickness is &lt; 20 nm (see Figure).