Decomposition Of GaAs Research Articles

Long-wave infrared laser irradiation damage effect on GaAs/AlGaAs quantum well infrared photodetector

The damage effect and mechanism of laser irradiation on long-wave focal plane array (FPA) GaAs/AlGaAs quantum well infrared photodetector (QWIP) were preliminarily explored by using numerical simulation and experiment methods. Piecewise functions were employed to simulate the complex boundary structure of the QWIP, enabling the numerical simulation investigation of mono-pulse, nano-second, long-wave infrared laser irradiation damage effect on the QWIP. The highest QWIP temperature, the highest surface temperature and the maximum circumferential thermal stress were analyzed in relation to laser energy density. The pulse average energy density thresholds of thermal decomposition damage, melting damage and thermal stress-induced damage were theoretically obtained. Preliminary experiments were then conducted by using a mono-pulse, nano-second, 7.2 μm all-solid-state long-wave infrared laser. The experimental results revealed a point-shape damage in QWIP response measurement after the irradiation by a laser pulse of average energy density 1.30 J cm−2, due to the decomposition of GaAs. At a higher average energy density 5.42 J cm−2, both melting and stress-induced damages appeared, with the damage morphology predominantly influenced by stress-induced damage, resulting in the occurrence of blind pixels or the losing of pixels. Furthermore, at laser pulse average energy density 12.48 J cm−2, line-shape damage of the QWIP was observed.

Microstructural evolution in self-catalyzed GaAs nanowires during in-situ TEM study

The microstructural evolutions in self-catalyzed GaAs nanowires (NWs) were investigated by using in situ heating transmission electron microscopy (TEM). The morphological changes of the self-catalyst metal gallium (Ga) droplet, the GaAs NWs, and the atomic behavior at the interface between the self-catalyst metal gallium and GaAs NWs were carefully studied by analysis of high-resolution TEM images. The microstructural change of the Ga-droplet/GaAs-NWs started at a low temperature of ∼200 °C. Formation and destruction of atomic layers were observed at the Ga/GaAs interface and slow depletion of the Ga droplet was detected in the temperature range investigated. Above 300 °C, the evolution process dramatically changed with time: The Ga droplet depleted rapidly and fast growth of zinc-blende (ZB) GaAs structures were observed in the droplet. The Ga droplet was completely removed with time and temperature. When the temperature reached ∼600 °C, the decomposition of GaAs was detected. This process began in the wurtzite (WZ) structure and propagated to the ZB structure. The morphological and atomistic behaviors in self-catalyzed GaAs NWs were demonstrated based on thermodynamic considerations, in addition to the effect of the incident electron beam in TEM. Finally, GaAs decomposition was demonstrated in terms of congruent vaporization.

Kinetics of Au-Ga Droplet Mediated Decomposition of GaAs Nanowires.

Particle-assisted III-V semiconductor nanowire growth and applications thereof have been studied extensively. However, the stability of nanowires in contact with the particle and the particle chemical composition as a function of temperature remain largely unknown. In this work, we use in situ transmission electron microscopy to investigate the interface between a Au-Ga particle and the top facet of an ⟨1̅1̅1̅⟩-oriented GaAs nanowire grown via the vapor-liquid-solid process. We observed a thermally activated bilayer-by-bilayer removal of the GaAs facet in contact with the liquid particle during annealing between 300 and 420 °C in vacuum. Interestingly, the GaAs-removal rates initially depend on the thermal history of the sample and are time-invariant at later times. In situ X-ray energy dispersive spectroscopy was also used to determine that the Ga content in the particle at any given temperature remains constant over extended periods of time and increases with increasing temperature from 300 to 400 °C. We attribute the observed phenomena to droplet-assisted decomposition of GaAs at a rate that is controlled by the amount of Ga in the droplet. We suggest that the observed transients in removal rates are a direct consequence of time-dependent changes in the Ga content. Our results provide new insights into the role of droplet composition on the thermal stability of GaAs nanowires and complement the existing knowledge on the factors influencing nanowire growth. Moreover, understanding the nanowire stability and decomposition is important for improving processing protocols for the successful fabrication and sustained operation of nanowire-based devices.

Self-Running Ga Droplets on GaAs (111)A and (111)B Surfaces

Thermal decomposition of GaAs (111)A and (111)B surfaces in ultrahigh vacuum results in self-running Ga droplets. Although Ga droplets on the (111)B surface run in one main direction, those on the (111)A surface run in multiple directions, frequently taking sharp turns and swerving around pyramidal etch pits, leaving behind mixed smooth-triangular trails as a result of simultaneous in-plane driving and out-of-plane crystallographic etching. The droplet motion is partially guided by dislocation strain fields. The results hint at the possibilities of using subsurface dislocation network and prepatterned, etched surfaces to control metallic droplet motion on single-crystal semiconductor surfaces.

Defects of GaAs Crystals Grown by the Pulling-Down Method

Compound semiconductor GaAs crystal was grown by the pulling-down method and the Φ2" GaAs boules were obtained. The growth defects, such as growth stripes, small facets, pits and dislocations, were observed. The pits on the surface of the boule was attributed to the water content of B2O3 encapsulant and the growth defects on the tail were associated with the evaporation of As due to GaAs decomposition. The average EPD (etch pit density) was measured less than 5000 cm-2, which shows the pulling-down method was a potential technique to grow high quality GaAs crystals.

Cubic GaN growth on (311)A GaAs substrate by MOVPE

AbstractCubic GaN layers has been grown on (311)A GaAs substrates by MOVPE at relatively high growth temperature at 900 °C. Cubic GaN (311) grew on the (311)A GaAs with and in‐plane epitaxial relationship of [01‐1]GaN//[01‐1]GaAs and [200]GaN//[200]GaAs. Full width at half maximum of the cubic GaN (002) X‐ray rocking curve is less than 20 arc min, which is comparable to that of the cubic GaN grown on (001) substrate. The lattice constant is in the range of 4.502 to 4.506 Å. Even at the growth temperature as high as 900 °C, the interface between cubic GaN layer and GaAs substrate is remarkably smooth without any voids, owing to the suppression of the (111) surface steps on the (311)A substrate surface. These results indicate that the (311)A‐oriented GaAs is a candidate substrate for the MOVPE growth of cubic GaN layer in avoiding the thermal decomposition of GaAs and in improving the interface and surface morphologies. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical properties and ultrafast photo-response of InGaAs/InP grown by low-temperature molecular beam epitaxy with a GaAs decomposition source

Lattice-matched InGaAs on (1 0 0) InP was grown by molecular beam epitaxy with arsenic dimers (As 2) at a growth temperature ( T g) range of 250–470°C. Measurements of double-crystal X-ray diffraction reveal that Δ a ⊥/ a o of low-temperature-grown (LTG) InGaAs increases from 0.82×10 −2 ( T g=470°C) to 4.1×10 −2 ( T g=250°C) as T g decreases. The measurements also indicate that excess arsenics are easily incorporated as antisites. All grown samples show a clear crystalline structure and are strong n-type. When T g is decreased from 470°C to 250°C, then according to the Hall measurement the carrier concentration increases from 5.0×10 −16 to 2.4×10 −18 cm −3 and according to the time-resolved reflectivity measurement the carrier lifetime decreases from 14.02 to 2.33 ps. Finally, for InGaAs/InP grown at 250°C, the incorporation of Be decreases the carrier lifetime to 1.86 ps and the residual n-type carrier concentration to 5.0×10 −16 cm −3. Crystallized InGaAs/InP with LTG material properties was obtained with a smaller V/III ratio and at higher growth temperature, compared to those with As 4.

A novel evaluation method to determine the fractal dimension of SEM images: a study of Au/Pd/GaAs contacts during heat treatment

Heat treatment is an essential technological step for making ohmic contacts to compound semiconductors. During the heat treatment a remarkable volatile component (arsenic) loss takes place due to the thermal decomposition of GaAs and the interactions between Ga and the contact metals. Using a scanning electron microscope combined with a mass spectrometer it was possible to examine the changes of the surface pattern and to measure the As evaporation. We introduced a new method (soft segmentation) to determine the fractal dimension of multi-cluster images.

Uniform growth of high-quality 2-in diameter In 0.53Ga 0.47As/In 0.52Al 0.48As/InP and In 0.2Ga 0.8As/GaAs/AlGaAs multi-quantum well wafers by MBE with GaP and GaAs decomposition sources

Uniform In 0.53Ga 0.47As/In 0.52Al 0.48As/InP multi-quantum well (MQW) and In 0.2Ga 0.8As/GaAs/AlGaAs graded-index separated-confinement double QW wafers have been grown by molecular beam epitaxy (MBE) with GaP and GaAs decomposition sources using indium-free holder on 2-in substrate. This was achieved by uniform temperature distribution, which was obtained by the introduction of a thermally shielded substrate manipulator; a stable DC power supply; a highly conductive silicon back plate; and a uniform distribution of arsenic dimer on substrate by GaAs decomposition source. For InGaAs/InAlAs MQWs grown by MBE, the uniformity (standard deviation) was measured by scanning photoluminescence (PL) taken at T=300 K, and was found to be 1538±1.2 nm. The uniformity of InGaAs/GaAs double QW was 987.6±1.0 nm, which is the best data ever reported. The optical quality of two samples was investigated by PL taken at T=9 K. The PL linewidths were 7.1 and 4.68 meV for InGaAs/InAlAs and InGaAs/GaAs QWs, respectively. The optical quality of the reported samples is comparable to the best data reported for the same structure grown by various epitaxial methods.

MOCVD Growth of Cubic Gallium Nitride: Effect of V/III Ratio

We have grown cubic GaN on GaAs(001) substrates by MOCVD using a double step process with a buffer deposition at 400 °C. The purpose of the buffer deposited at very low temperature is to prevent GaAs decomposition at growth temperature. We have focused on the effect of the NH3/TEGa molar ratio on the growth of this metastable phase. We have assessed the crystalline quality using X-ray diffraction in the θ–2θ mode, and have used low temperature (2 K) PL for evaluating the optical properties of the GaN films. We found an optimum V/III ratio of 1250 at the growth temperature of 800 °C.

Mechanism of GaAs transport by water reaction application to the growth of thick epitaxial layers

We study in detail the decomposition of GaAs by water, and show that the growth technique of epitaxial layers based on this reaction can lead to growth rates reaching several μm per minute. This opens an economical access to the production of semi-insulating and thick epitaxial layers. We briefly mention that these layers can exhibit electronic properties allowing their use in various fields such as high power electronics, photodetection and micro-electronics (production of very homogeneous semi-insulating layers).

Surface Composition of n‐GaAs Cathodes during Hydrogen Evolution Characterized by In Situ Ultraviolet‐Visible Ellipsometry and In Situ Infrared Spectroscopy

The chemical composition of (100) n‐GaAs electrode surfaces has been studied for the first time during cathodic hydrogen evolution in acidic aqueous solutions by in situ spectroscopic techniques. Cathodic decomposition of GaAs is observed in the entire potential range where hydrogen evolution occurs, decomposition products being or and or , depending on the potential. In situ UV‐visible ellipsometry shows unambiguously that the surface is partially covered by metallic gallium at sufficiently negative potentials. In situ infrared spectroscopy in the differential mode reveals that when hydrogen evolution occurs, hydrogen always binds to arsenic atoms, not to gallium atoms. The sub‐monolayer hydrogen coverage is approximately linear with the applied potential and shows hysteresis upon cycling of the applied potential. A correlation between hydrogen surface coverage, current density, and applied potential gives direct new evidence that an increase in the hydrogen surface coverage of GaAs electrodes causes a negative shift of the flatband potential. Measurements of the time response of hydrogen surface coverage to changes of the applied potential provide the first direct evidence that hydrogen evolution follows a Volmer‐Heyrovský route.

Formation of heavily doped semiconductor layers by pulsed ion beam treatment

The formation of heavily doped Si and GaAs layers using implantation and powerful pulsed ion beams has been investigated. The influence of the depth distribution of energy released by the ions on the temperature profile and the electrically active impurity distribution in Si and GaAs is analyzed. It is shown that as a consequence of the simultaneous action of impurity diffusion processes normal to the surface and decomposition of GaAs at the surface, the heavily doped (8 × 10 19cm −3) layers are formed in the subsurface region (0.1–0.5 μm).

Periodic supply epitaxy: a new approach for the selective area growth of GaAs by molecular beam epitaxy

Selective growth of GaAs on a GaAs substrate with a SiO 2 patterned mask has been carried out by molecular beam epitaxy at 630°C, using molecular beams of Ga and As 4 as sources and employing a periodic supply epitaxy technique for the first time. The GaAs crystalline nuclei deposited on the mask surface are decomposed and the atoms adsorbed on the mask surface are evaporated or allowed to migrate until they are captured by the single crystalline epitaxial layer. A wide depleted zone is then formed and the polycrystals of GaAs are located beyond this area. The surface migration is shown to influence drastically the thickness of the grown layer. The epitaxial layer obtained is flat and smooth even for the (001) substrates, since the lateral flux prevents the decomposition of GaAs on the free surface of the epitaxial layer. The growth technique is discussed in details, together with an analysis of the important parameters for the selective growth by periodic supply epitaxy.

Structural Decomposition at Sn/GaAs(001) Interface

ABSTRACTMorphological studies of the system Sn/GaAs(001) are required to interpret electronic anomalies of devices which include doped III-V MBE grown thin films. Previous studies focused on the dynamics of Sn on As terminated surfaces. The current study complements those studies on a Ga terminated surface, i.e., conditions which may occur locally for short periods during MBE growth.Sn is deposited on in-situ cleaned Ga rich GaAs(001) surfaces and the evolution of morphological structures is presented as a function of annealing temperature and Sn supersaturation. Three distinct regimes were observed, (i) a low temperature range (T ≤ 500°C) where Sn shows a propensity toward three-dimensional clustering, (ii) an intermediate temperature range (500°C ≤ T ≤ 625°C) where a transition in the morphology occurs due to strong interactions with the substrate resulting in the formation of characteristic etch-patterns and (iii) a high temperature regime (T ≥ 650°C) where the thermal decomposition of GaAs dominates while the deposited Sn desorbs fast.

Evolution of the microstructure of Au(Zn) metallization during formation of an ohmic contact to p-type GaAs

Structural processes occurring in thin Au(Zn) metallization during the formation of ohmic contact to p-type GaAs have been investigated by X-ray diffraction, secondary-ion mass spectrometry, transmission electron microscopy and high resolution electron microscopy. In order to examine the release of arsenic during thermal processing, a thin film collector method was applied. Emphasis was placed on the particular role of each of metallization constituents during consecutive stages of the formation of an ohmic contact. Pure Zn was found to penetrate the native oxide on GaAs surface and to form an ohmic contact after annealing at 220°C. The addition of Zn into the Au metallization suppresses the thermally induced decomposition of GaAs and stabilizes the size of Au grains, forming the α 3-AuZn phase. The most important aspect of the GaAsAu reaction is the formation of Ga vacancies in the subcontact region. They are required to form a low resistance ohmic contact to p-type GaAs, since the specific resistance of the Au(Zn) contact is one order of magnitude lower than that of the pure Zn contact.

Optimal surface cleaning of GaAs (001) with atomic hydrogen

Atomic hydrogen is commonly used to clean GaAs surfaces. The goals of this work are to optimize the cleaning process and to control surface reactions in order to avoid decomposition of GaAs. Chemically polished GaAs (001) surfaces have been cleaned by thermally generated atomic hydrogen and analyzed by surface sensitive techniques. We propose an optimal process involving two exposures. The first one at room temperature etches As oxides. The second one at 300 °C completes the reduction of Ga oxides. We demonstrate that the variations of the ionization energy, work function, and Fermi level are very sensitive to the completion of the cleaning reaction. These parameters can be used to monitor surface reactions on-line in order to avoid excessive desorption of As and GaAs decomposition.

Contact Resistivity Dependence on Ge:Ni Ratio in AuNiAuGe Metallization on n-GaAs

It is found that the Ni:Ge ratio in AuGeNiAu metallization on n-GaAs determines the optimally low contact resistance condition independent of the Au layer thickness. In two series of experiments the thickness x of the Ni layer was varied in the structure Au/Ni/Ge/Au with layer thicknesses of 600/x/50/100 nm and 600/x/100/200 nm. Optimally low contact resistivity of 6.4×10-6 Ω cm2 and 1.68×10-5 Ω cm2, respectively, were obtained when the Ni:Ge layer thickness ratio reached 1. Secondary-ion mass spectroscopy showed that, at this Ni:Ge ratio of 1, maximum Ge doping on the n-GaAs was obtained. Such a condition is a result of a balance between the catalytic effect of Ni on the decomposition of GaAs by Au for effective doping by Ge, to achieve low contact resistance, and the formation of NiAs, rather than Ni2GeAs, under the excess-Ni condition, which results in an increase of contact resistivity.

Quantitative analysis of arsenic losses during the formation of Au(Zn)/p-GaAs ohmic contacts

The formation of Au(Zn)/p-GaAs ohmic contacts by furnace annealing either in open or closed configurations with a dielectric cap has been investigated. Evaluation of the extent to which the GaAs substrate decomposes under these conditions was of primary concern. This was studied by measuring the amount of As losses, using the Cr-collector method, and correlating this with the amount of Ga diffused into the Au(Zn) metallization. The thermally induced decomposition of GaAs in contact with Au(Zn) metallization strongly depends on both the application of the capping layer, and on the thickness of the metallization. The loss of As is reduced to 6×1014 atom/cm2 using thin 10 nm Au/10 nm Zn/30 nm Au metallization annealed with a insulating capping layer deposited by sputtering. Electrical measurements indicate that under these conditions good ohmic contacts are obtained. Thus, the contact reaction sufficient to produce good ohmic contacts can be limited to about one monoatomic layer of GaAs.

Tem Analysis of Interfacial Reactions Between TiWn, Wn Gate Metallizations and GaAs in Mesfet Devices

AbstractIn an effort to improve the uniformity of the threshold voltage, the Schottky barrier height, and the ideality factor, Ti0.29W0.52N0.19 and W0.81N0.19 gate metal depositions have been investigated as a function of annealing conditions for GaAs based MESFET devices. Crosssectional TEM samples were made of each device. The results of these studies indicate there is a systematic and significant reaction occurring between the gate metal and the GaAs upon 850°C and 900°C rapid thermal annealing. These reactions take different forms depending on whether Ti is present or not. If Ti is absent (i.e. WN gates) then the interfacial roughness between the gate and the GaAs is less than 30Å indicating the metallization is very unreactive. The WN contacts for some gates show void formation indicative of GaAs decomposition also for some devices an amorphous layer is observed at the interface. Selected area diffraction patterns indicate only the alpha-W and beta-W2N phases are present. For the TiWN gates the interface roughness is as large as 200Å upon 900°C 10 second RTA. However no voids or interfacial amorphous layers were observed. Again only alpha-W and beta-W2N were observed in the bulk of the gates. For both systems, beta-W2N appears to form at the interface however the morphology of the beta-W2N grains are much larger for the TiWN gates. Electrical results indicate the TiWN gates have a lower ideality factor (near 1.1) and greater uniformity across the wafer compared to the WN gates. It is proposed that the presence of Ti in the gate metal aids in reducing any surface oxides thus improving the ideality and uniformity of the gate metal/GaAs contact.