GaAs Crystal Surface Research Articles

UV laser-induced nanostructured porous oxide in GaAs crystals

Laser processing is an important tool for inducing local topographical and chemical changes on the surface of technologically important materials to facilitate various device fabrication procedures or to favor chemical reactions. Here, we report that irradiation of GaAs crystal surfaces with c.w. UV laser radiation (λ = 244 nm) in ambient conditions produces a well defined layer of porous oxide with a thickness up to ∼0.4 μm. Under certain laser irradiation conditions the oxidized layer appears to self-organize into periodic features, collectively known as laser-induced periodic surface structures (LIPSS). The topography and composition of the laser grown surface oxide layer is investigated.

Studying structure of thin copper phthalocyanine films by reflectance anisotropy spectroscopy

The structure of thin molecular films of copper phthalocyanine (CuPc) on crystalline GaAs(001) and glass substrates has been studied by the method of reflectance anisotropy spectroscopy. It is shown that, using this method, it is possible to determine the orientational anisotropy in CuPc layers. It is established that the GaAs crystal surface produces orienting action on the molecular structure of CuPc films, while a glass substrate does not exhibit this effect. A model of the anisotropic reflection of light is considered that provides satisfactory description of the orientation-related features in the spectra of thin CuPc films as dependent on their thicknesses.

Effect of roughness on the phase velocity of Rayleigh waves in GaAs crystals

The phase velocity dispersion of the Rayleigh waves on surfaces of GaAs crystals having different roughness has been measured by laser-acoustic wave equipment. Applied model of a rough film with zero elastic moduli explained the effect of roughness on the acoustic surface wave phase velocity and showed good coincidence with the experimental data.

RHEED Observation of Tin Atomic Chains Formation on Vicinal Gallium Arsenide Plane

AbstractIn the present work by means of measurements of RHEED intensity the research of the arrangement of tin atoms on vicinal surfaces of GaAs crystals was carried out. The orientation of crystals was close to (001). The intensity of diffracted electrons was measured in different points of the diffraction picture to reveal the arrangement of tin atoms on terraces or on edges of terraces. It was shown that tin atoms may decorate edges of terraces and thus form chains. Concentrations of tin atoms located on terraces and their edges were established. It was revealed, that tin atoms decorate edges of terraces only at rather high temperatures of a substrate.

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species SiGa+ and as shallow acceptor species SiAs-. The solubility of SiAs- is much lower than that of SiGa+ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is SiGa+ which will convert into SiAs- in accordance with their solubilities and that the point defect species governing the diffusion of SiGa+ are triply-negatively-charged Ga vacancies VGa3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n+-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently.

Steam oxidation of GaAs

The steam oxidation of GaAs is characterised. In the temperature range 500 – 520°C the steam process forms a dense, smooth GaxOy film characterised by a volume contraction of 5 – 10%. The oxidation process is readily masked by SiO2, and can therefore be applied selectively to a GaAs crystal surface.

Low-energy cathodoluminescence experiment with polarized electrons and a negative-electron-affinity GaAs target.

We report new measurements of circularly polarized recombination radiation from highly doped p-type GaAs emitted under impact of longitudinally polarized electrons with an initial kinetic energy varied between 2 and 10 eV. The work function of the target crystal is lowered by cesiation and oxidation of the surface. The results are discussed and compared with our earlier measurements on a clean GaAs crystal surface and with photoluminescence data.

Ammonia chemisorption on gallium arsenide clusters

Gallium arsenide clusters in the 6–16-atom size range were generated by laser vaporization in a supersonic nozzle and trapped as positive ions in Fourier transform ion-cyclotron resonance mass spectrometer. Measurements of the rate of attachment of ammonia revealed that all clusters larger than seven atoms were most reactive near the 1 1 composition ratio of gallium/arsenic. The results suggest that even at this small size the clusters begin to adopt the alternating gallium—arsenic bonding arrangement characteristic of bulk GaAs crystal surfaces where gallium—arsenic bonding activates gallium atoms for ammonia chemisorption.

Mechanism of gallium arsenide MOCVD

There are many points to be elucidated as to the chemical reactions between TMG and AsH 3. We have examined the vapor species in a MOCVD reactor by means of ir absorption spectroscopy and mass spectroscopy. The gas phase reaction of TMG with H 2 occurs above 400°C, giving rise to Ga deposition and CH 4 generation. On the other hand, the pyrolitic reaction of TMG takes place above 600°C in the absence of H 2, leading to Ga deposition and the generation of CH 4, C 2H 4, etc. In the mixture of TMG and AsH 3, an unidentified species which corresponds to 2080 cm −1 absorption spectrum is detected. Mass spectroscopic analysis reveals that a complex of the 2080 cm −1 spectrum is AsH(CH 3) 2 or AsH 2CH 3. In the case of AsH 3, AsH 3 decomposes catalytically on the surfaces of GaAs crystals. The dependence of the decomposition rate on the orientation of the GaAs surface and the Ga melt has been studied. The catalytic effect is largest on the (111)A surface and decreased in the order of the Ga melt and the (100) surface. The catalytic effect is not observed on the (111)B surface. Namely, the catalytic reaction rates depend on the density of Ga-single bonds. It is likely that the final species adhered to the (111)A at the largest rate in MOCVD is GaAs.

Mass spectrometric analysis of gas molecule adsorption on solid

Molecular layer epitaxy (MLE) is a crystal growth method to prepare perfect crystal films and can regulate the thickness of the epitaxial layer to the order of atomic accuracy. In this method alternate exposures of trimethylgallium (TMG) (or other Ga gases) and AsH 3 to GaAs crystal surface materializes the monomolecular layer growth of GaAs. The reaction mechanisms have been studied by means of in-situ mass spectroscopy. The results have indicated that under normal growth conditions the monomolecular layer adsorption species is GaCH 3, which reacts with AsH 3 and produces a monomolecular layer of GaAs.

Surface and bulk structural defects in Hg1−xCdxTe

The techniques of optical microscopy and transmission electron microscopy (TEM) have been used to study the structural characteristics of a surface of a solid state recrystallized Hg1−xCdxTe crystal (x=0.35) cleaved at room temperature. Such surfaces are of special interest because of their wide use in photoemission spectroscopy studies. HgCdTe cleaved surfaces were found to be much rougher than similar surfaces of GaAs crystals, containing numerous steps and regions where fracture was clearly ductile rather than brittle. TEM observations indicate that a step is associated with numerous dislocations where the crack presumably arrested prior to changing direction, implying that the room temperature cleaved surface has a high defect density compared to the bulk crystal. TEM has also been used to characterize the defects associated with etch pits developed using ‘‘Polisar etch 2’’ on the (111)A face of a Hg1−xCdxTe crystal grown by the solid state recrystallization process. While in some cases dislocations were found, a much higher proportion of etch pits were observed to be associated with precipitates, believed to be Te. In general, these precipitates were isolated, although occasionally they were associated with a dislocation line. The form of the precipitates, along with the distribution of the etch pits, suggests that the final defect structure is strongly influenced by the casting stage.

The electronic structure of defects in amorphous GaAs

Abstract The local electronic structure of like-atom bonds and threefold coordinated Ga and As sites (dangling bonds) in amorphous GaAs have been calculated by the tight-binding recursion method. Singly occupied dangling bonds are found to give gap states just inside the band edges, but their relaxed diamagnetic configurations only give band resonances. This behaviour differs from a-Si: H but is similar to that on surfaces of GaAs crystals. Ga-Ga bonds do not give gap states, but isolated As-As bonds give states just below the conduction-band edge.

Cleaning of Si and GaAs Crystal Surfaces by Ion Bombardment in the 50–1500 eV Range: Influence of Bombarding Energy and Sample Temperature on Damage and Incorporation

Silicon and gallium arsenide single crystals were cleaned in high vacuum by very low energy ion bombardment. High currents (up to 1 mA/cm2) were produced by a triplasmatron source down to energies of 50 eV. In situ Auger analyses showed that Si and clean surfaces are obtained at room temperature for bombarding energies as low as 70 and 50 eV, respectively. The incorporation of bombarding ions and the bombardment‐induced disorder were studied ex situby Rutherford backscattering and channeling. For silicon, the incorporation (Ar or Xe) increases linearly with bombarding energy while the Auger signal saturates above 200 eV. This result indicates that at high energies, ions are incorporated at greater depths than the sampling depth of the Auger technique. For , ion incorporation takes place only above 200 eV. The bombardment‐induced disorder increases with the bombarding energy. Above 200 eV, a strong correlation was observed between incorporation and disorder, demonstrating that the latter was stabilized by the incorporated ions. However, at very low energies, a significant disorder remains (, for Si and , respectively) for a very small concentration of incorporated ions, indicating the presence of “intrinsic disorder” related to the sputtering mechanism. No influence of the beam current on bombardment‐induced incorporation or disorder was detected. For silicon, at very low bombarding energies, the disorder increases with the sample temperature during bombardment, with a noticeable effect already observed at 100°C. This is due to bombardment‐enhanced diffusion of the ions and associated damage stabilization. At higher bombarding energies, no temperature dependence was observed because the range of bombarding ions was greater than the diffusion length.

Degradation of photoluminescence intensity caused by excitation-enhanced oxidation of GaAs surfaces

Rapid degradation of photoluminescence (PL) intensity under high excitation level (∼1 kW/cm2) was observed at fresh surfaces of GaAs crystals made by various growth methods. The Auger analyses showed quick oxide formation at the photoexcited GaAs surfaces. The degraded PL intensity was recovered by etchings only the oxide layers; thus, the cause of PL degradation was ascribed to the increase of nonradiative recombination at the oxide-GaAs interface. The oxidation process was proved to be athermal. In contrast to GaAs, Al0.3Ga0.7As and InP showed no or slow degradations, respectively, under the same excitation condition.

後方散乱法を用いたマイクロアナリシス

A new microanalysis using backscattering method was applied to measure lateral distributions as well as depth distributions of impurities in semiconductors. High energy He+-beam from the Van de Graaff accelerator could be squeezed to 70500μmφ on the target by means of the quadrupole magnetic lens and slits system. The lateral distributions of impurities in semiconductors were measured by step scanning i.e, by using a goniometer which slides the targets along the direction perpendicular to the beam line with a minimum step of 10μm.The microanalysis was applied to measure the lateral and depth distributions of Au atoms at GaAs crystal surface sintered in the nitrogen atmosphere after Au evaporation to GaAs crystal surface. It was found that the lateral distributions were not uniform either on the surface or in the bulk. Au atoms were diffused abnormally to the deep region in GaAs crystals, and the concentration profiles of Au were not fitted to complementary error functions. Also presented are the measured results of distributions of Sn doped into Si by means of two different techniques, i.e, doped oxide method and CZ pulling method.

Bombarding Effects of GaAs Crystal Surface

Bombarding Effects of GaAs Crystal Surface