摘要:

Epitaxy of III–V semiconductor layers from gaseous sources metalorganic chemical vapor depsoition and metalorganic molecular‐beam epitaxy is essentially determined by surface reactions of metalorganic components on the semiconductor surface. The present paper deals with the decomposition of trimethylgallium [TMGa=Ga(CH3)3] and trimethylarsenic [TMAs=As(CH3)3] on Si(111) and Si(100) surfaces. High‐resolution electron energy‐loss spectroscopy (HREELS) is used to identify the adsorbed surface species by means of its vibrational spectrum. Adsorption of TMGa and TMAs is performed at 300 K and the surface reaction, in particular its dependence on temperature is studied by measuring HREELS spectra after each step. A comparison with thermal desorbtion data is given in some cases. TMGa and TMAs exhibit a different decomposition pattern and the reaction of TMAs is dependent on the orientation of the Si surface.

ISSN:0734-211X    

DOI:10.1116/1.584632

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The decomposition of triethylgallium (TEG) on Si(100) is studied using temperature programmed desorption, x‐ray photoelectron spectroscopy, and electron energy‐loss spectroscopy. It is found that TEG adsorbs molecularly. It then decomposes mainly by a simple β‐hydrogen elimination mechanism yielding ethylene and adsorbed hydrogen. The ethylene desorbs in a peak centered at 600 K while the hydrogen desorbs in a sharper peak at 820 K. There is some carbon incorporation which is attributed to adsorption of an ethylene impurity. However, there is no evidence for carbon deposition during the TEG decomposition process itself.

ISSN:0734-211X    

DOI:10.1116/1.584633

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Thin films of FexAlyhave been grown by molecular‐beam epitaxy on InP(100) substrates. Before growth of the epitaxial intermetallic alloy a 0.2‐μm InAlAs buffer and a ten‐layer AlAs diffusion barrier were deposited. Initial films were grown at 200 °C and were stable up to at least 600 °C. Upon the initiation of growth the reflection high‐energy electron diffraction intensity was observed to decrease slowly and then exhibited oscillations corresponding to layer‐by‐layer growth. There was a short incubation period before the onset of the intensity oscillations that depended upon the ratio of the Fe and Al fluxes. The shape of the specular beam was measured versus incident angle and indicates that the surface is nearly as smooth as the starting AlAs surface. Upon heating to 550 °C the beams became sharper yet. Growth on the annealed surface at 200 °C gave intensity oscillations that were an order of magnitude stronger. Initial attempts to grow epitaxial AlAs on top of the FeAl layer showed three‐dimensional island growth.

ISSN:0734-211X    

DOI:10.1116/1.584635

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Distinct differences in the nucleation of Al at room temperature on arsenic‐stabilized (2×4)‐ andc(4×4)‐GaAs(001) surfaces grown by molecular‐beam expitaxy have been observed with reflection high‐energy electron diffraction. The nucleation of Al is found to be dependent upon the amount of disorder on the (2×4)‐GaAs(001) surface. Phase diagrams showing the MBE growth parameters required for the preparation of more ordered versus more disordered surfaces of GaAs(001) have been constructed. The presence of disorder has been found to be independent of the rate of cooling of the GaAs substrate to room temperature for Al deposition. Nucleation on the more‐disordered (2×4) surface and on thec(4×4) surface are similar in the direction of twofold periodicity, but differ in the direction of fourfold periodicity. The presence of a strong Al metal adatom–adatom interaction of submonolayer coverages, formerly reported for Al/(2×4)‐GaAs(001), may help to explain why the more‐ordered (2×4)‐reconstructed surface preferentially nucleates fcc Al(110).

ISSN:0734-211X    

DOI:10.1116/1.584637

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Continuum elastic theory is applied to the formation of misfit dislocations and point defects in strained layer structures. Explicit calculations of the energies of misfit dislocations in the double‐ and single‐kink geometries yield line tensions below which strained films are stable with respect to defect formation. Our results yield a mismatch‐dependent stability limit which, in the double kink case, differs from the Matthews–Blakeslee model by a geometrical factor and by the addition of a stress term associated with climb of the misfit dislocation. While our calculations yield equilibrium stability limits which may not correspond to observed critical thicknesses, the calculated stresses may be applied to descriptions of the kinetics of strain relief in films grown beyond these limits. Last, calculations of strain‐related contributions to the free energy of formation of point defects suggest a contribution ‖ΔGstrain‖ ≂0.25 eV for a 5% lattice mismatch. This suggests a means of suppressing or enhancing the formation of vacancies or interstitials in semiconductors favoring these defects.

ISSN:0734-211X    

DOI:10.1116/1.584639

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The morphology of interfacial dislocations in molecular‐beam epitaxy (MBE) grown GaAs/InxGa1−xAs/GaAs thin films (60–300 nm,x=0.15–0.40) on GaAs(100) undergoes a transition with increasingxfrom rectangular arrays, with dislocations lying in the 〈011〉 directions, to random tangled arrays, with a reduced preference for crystallographic orientation. Films with intermediatexvalues exhibit both types of morphology in separate areas. For a givenxvalue the interfacial dislocation density increases with increasing thickness. A marked asymmetry in the dislocation density in the [01̄1] and [011]directions is observed in some of the films exhibiting rectangular arrays for specific values of InxGa1−xAs film thickness above the critical value. The asymmetry is not observed in thicker InxGa1−xAs films. This asymmetry is attributed to different mobility of α and β dislocations. The rectangular array morphology is found in a number of lattice‐mismatched systems, including early observations in GaAsxP1−x/GaAs, while the random arrays are representative of recent observations in GaAs/Si. The measured dislocation densities in the InxGa1−xAs /GaAs system are generally inadequate to relax the interfacial strain, implying a significant partitioning of strain between elastic and plastic components. In 300 nm thick films, a dislocation pinning reaction was directly observed. This reaction is most probably responsible for (1) creating dislocation sources that facilitate strain relaxation in the early stages of strain relaxation, and (2) inhibiting dislocation motion in the latter stages of strain relaxation by pinning dislocations, thus producing a high density of threading dislocations. These observations were enabled by a new technique for preparing large‐area electron transparent films, which required no thinning by ion milling or any other method.

ISSN:0734-211X    

DOI:10.1116/1.584640

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Measurements of critical layer thicknesses and strain relaxation have been made for AlSb on GaSb(001) using ion scattering/particle induced x‐ray techniques. The maximum strain in the films agrees well with that calculated from bulk elasticity data. The critical thickness as measured by the ion channeling experiment is ≊140±30 Å. Films exceeding the critical thickness do not relieve the strain immediately but rather show a gradual relaxation up to ≊1000 Å. The results are compared with theoretical models of strain relief and critical thickness. Issues related to the protection of the AlSb films from oxidation, beam damage, and the use of particle‐induced x‐ray emission have been addressed. A protective cap of ≊200 Å of Be was found to give the best performance.

ISSN:0734-211X    

DOI:10.1116/1.584641

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Strain relaxation in Si1−xGex/Si superlattices and alloy films is studied as a function ofexsituanneal treatment with the use of x‐ray diffraction and Raman spectroscopy. Samples are grown by molecular‐beam epitaxy at an unusually low temperature (≊365 °C). This results in metastably strained alloy and superlattice films significantly in excess of critical thicknesses previously reported for such structures. Significant strain relaxation is observed upon anneal at temperatures as low as 390 °C. After a 700 °C, 2 h anneal, superlattices are observed to relax less fully (∼43% of coherent strain) than corresponding alloys (∼84% of coherent strain). Also, the strain relaxation kinetics of a Si1−xGexalloy layer is studied quantitatively. Alloy strain relaxation is approximately described by a single, thermally activated, first order kinetic process having activation energyEa=2.0 eV. The relevance of our results to the microscopic mechanisms responsible for strain relaxation in lattice‐mismatched semiconductor heterostructures is discussed.

ISSN:0734-211X    

DOI:10.1116/1.584598

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

This paper reports on a study of the intrinsic stress and strain in thin films of SiO2prepared by the thermal oxidation of crystalline silicon. We focus on the relationship between the inhomogeneity of thin‐film properties and the thermal history of the oxide film, including both film growth and thermal annealing. We show that this film can beinhomogeneousin the sense that oxide formed initially at the silicon–silicon dioxide (Si/SiO2) interface has beenannealedat the growth temperature for the time required for film growth, whereasnewlyformedoxide at the growth interface has not beenannealedfor any appreciable period. We demonstrate that thermal annealing cannot completely remove the thickness dependence in the strain induced by the mismatch between the molar volumes of silicon and silicon dioxide at the growth interface, subject to constraints introduced by the chemical bonding structure at that interface. Based on laser‐beam deflection and photoreflectance measurements, we show that there is alway a substantial residual intrinsic interfacial stress, and that is independent of the growth temperature, and thermal annealing. A time scale for describing thermal relaxation of stress and strain profiles is given by the ratio of process time to the viscoelastic relaxation time at the processing temperatures.

ISSN:0734-211X    

DOI:10.1116/1.584599

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We show that mismatched epitaxial growth on small growth areas results in metastable, low dislocation density films. By considering methods of dislocation nucleation in mismatched epitaxial films, we can explain the effect of growth area on the kinetics of misfit dislocation nucleation. We demonstrate this reduction of misfit dislocation density by growth on small areas using the InGaAs/GaAs system, and we also demonstrate a reduction in threading dislocation densities in the GeSi/Si system. InGaAs/GaAs interfaces which have a misfit dislocation density greater than 5000 dislocations/cm for large growth areas are grown nearly misfit‐dislocation‐free on small growth areas. GeSi/Si structures which have a threading dislocation density of approximately 1000 dislocations/cm2are grown with a 100% threading dislocation density reduction for small growth areas. We discuss the limits of growth on small areas to reduce both interface dislocation densities as well as threading dislocation densities.

ISSN:0734-211X    

DOI:10.1116/1.584600

出版商:American Vacuum Society    

年代:1989

数据来源: AIP