摘要:

We discuss the first real‐time optical spectroscopic measurements of (001) GaAs and AlAs surfaces during crystal growth by molecular‐beam epitaxy. In these experiments, reflectance–difference spectroscopy (RDS) is used to enhance the typically low sensitivity of optical probes to surface phenomena. Comparison of reflectance–difference and reflection high‐energy electron diffraction (RHEED) signals upon interruption of the As flux during otherwise normal growth of GaAs and AlAs shows that RD signals are sensitive to either surface chemistry or surface structure according to wavelength. The spectral dependence of the chemical component is sufficiently pronounced so that Al‐terminated surfaces can be distinguished from Ga‐terminated surfaces. We use this spectral capability to assess the competition between codeposited Al and Ga for the same surface‐bonding sites. We also report the first observation of the RD analog of RHEED oscillations, that is, oscillations in the RD response upon initiation of growth. These are seen to occur under both chemically and structurally sensitive conditions. The initial heteroepitaxial growth of GaAs on AlAs shows very complicated energy and time dependences that extend over a number of monolayers. These results suggest that systematic investigations of the optical properties of growth surfaces will lead to a new understanding of the fundamental mechanisms of crystal growth.

ISSN:1071-1023    

DOI:10.1116/1.584264

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The interaction of arsenic with the hydrogen‐terminated Si(111) surface has been studied using photoemission valence band and core level spectroscopy. The results are compared with those obtained previously for the interaction of arsenic with Si(111) and hydrogen with the arsenic‐terminated Si(111) surface. We have found that neither As nor H fully passivates the Si(111) surface with respect to the other species. Hydrogen can be removed from both the Si(111):As + H and Si(111):H + As surfaces by annealing, leaving As bonded to the Si(111) surface. A comparison is also made between arsenic‐terminated surfaces made with (i) an As4deposition onto a substrate whose temperature was varied from 800 °C down to 300 °C and (ii) a deposition at 300 °C followed by a 650 °C anneal. It is found that method (i) yields a surface with significantly better surface order.

ISSN:1071-1023    

DOI:10.1116/1.584265

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Cluster growth experiments of Ga on As terminated Si(111) are reported and shown to simulate Ga–As coevaporation in the case of low Ga and very low As fluxes. Based on these observations a model for GaAs clustering is proposed which explains qualitatively the absence of postdeposit clustering and can be quantified in order to be compared to recent substrate temperature dependent GaAs cluster size measurements by transmission electron microscopy techniques.

ISSN:1071-1023    

DOI:10.1116/1.584266

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Recently developed semiempirical potential energy functions for the Ga–As–Si and Ga–As–Al systems have been applied here to determine the excess formation energy for GaAs clusters on GaAs(001̄), AlAs(001̄), Si(001), and one atomic layer As‐covered Si(001) substrates as a function of cluster size and cluster shape by the Monte Carlo technique. Pyramidal type ledges on the GaAs clusters are found to be the favored ledge for the first three layers while an inverted‐pyramidal type ledge is also favored in certain cases for the As1/Si(001) substrate. Cluster formation at ledges is compared with cluster formation on a flat terrace for the Si(001) and the As1/Si(001) substrates.

ISSN:1071-1023    

DOI:10.1116/1.584267

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We simulate the epitaxial growth and annealing of GexSi1−xalloys on a Si(001) substrate using a stochastic Monte Carlo technique. Our simulation indicates that: (i) the overgrowth is defect‐free forx≤0.2, whereas defect formation is inevitable forx≥0.5; and (ii) initiation of phase segregation into Si and Ge(001) layers is obtained by means of solely surface diffusion effects during growth and annealing. These result from the kinetically more active nature of Ge atoms as compared to Si atoms, together with an effect arising from the compressive strain in the alloy layers.

ISSN:1071-1023    

DOI:10.1116/1.584268

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Time‐resolved photoluminescence spectra and decay data are presented for a series of type II (GaAs/AlAs) samples with different GaAs layer thicknesses. Low‐temperature delayed spectra reveal that the spectral lines shift gradually to lower energy with delay, and that the shift extends to ms time scales. At 6 K the decay curves of the type II emission contain power‐law and exponential components with rates ∼103s−1, indicating significant Γ–Xmixing, both by random and nonrandom processes. Both rates increase with temperature. The dependence of the decay rates and spectra on the GaAs layer thickness is examined. Models of the recombination mechanisms are discussed in the context of these new results.

ISSN:1071-1023    

DOI:10.1116/1.584270

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

A series of electrical measurements on double barrier resonant tunneling structures is described. It is shown that the bistability effect in the current–voltage characteristics of a double barrier structure can be removed by connecting a suitable capacitor to the external circuit. These measurements cast serious doubt on the recent interpretation of the bistability as an intrinsic space‐charge effect. The temperature dependence of the tunneling current at voltages below threshold is also investigated. An expression for the temperature and voltage dependence of the thermally activated resonant tunneling process is compared with experiment. Finally, the effect of hydrostatic pressure (up to 11 kbar) onI(V) characteristics is studied. It is found that, whereas the pressure has little effect on the low‐temperatureI(V) characteristics, the peak/valley ratio at room temperature is significantly reduced. This behavior is attributed to the effect of the higher conduction band minima.

ISSN:1071-1023    

DOI:10.1116/1.584271

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We use total yield photoelectron spectroscopy in combination with the Kelvin probe to study changes in the work function and the distribution of occupied band gap states upon boron doping and oxidation of amorphous hydrogenated silicon (a‐Si:H) surfaces. We observe 3×1011occupied surface states/cm2in clean undopeda‐Si:H in an 0.4‐eV wide band centered 5.0 eV below the vacuum level, which we ascribe to intrinsic surface defects. Incorporation of boron removes these states and exposes the intrinsic valence band tail, which is exponential over four orders of magnitude in the density of states. In contrast toc‐Si, where adsorbed oxygen decreases the large intrinsic surface state density (4×1014states/cm2) on the clean, cleaved surface, the relatively low density of intrinsic surface states ona‐Si:H allows the observation of oxygen‐inducedsurface band gap states. The origin of these states is discussed.

ISSN:1071-1023    

DOI:10.1116/1.584272

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

GaAs surfaces cleaved in ultrahigh vacuum and cooled to 100 K [low temperature (LT)] were exposed to molecular oxygen. Band bending as a function of exposure was measured with ultraviolet photoemission spectroscopy. Band bending on LTp‐GaAs is very small up to exposures>106L, whereas the same exposures give considerable band bending at room temperature (RT). Band bending on LTn‐GaAs is as fast as at RT. This situation is therefore opposite to that of metals/LT GaAs reported last year at this conference, but is analogous to that produced by Cl/GaAs at RT. These results can be interpreted in terms of simple adsorption of electronegative species which introduce an acceptor level deep in the GaAs gap. As for metals on LT GaAs, the nature of the surface states induced by the adsorption of single species dominates the position ofEFat low coverage. Metallicity dominates at high coverages of metals; oxidation‐induced defects dominate at RT or at higher exposures for O2/GaAs.

ISSN:1071-1023    

DOI:10.1116/1.584273

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Insulated gate electronic devices on InP and related III–V compound semiconductors have not to date achieved a level of performance adequate for commercial exploitation. This in part is believed to be due to the noncongruent dissociation of the group V element upon heating. In order to minimize such surface effects on InP, we have investigated two broad approaches; one involving the creation of an excess overpressure of phosphorous to suppress the anion loss; and one involving the creation of an ideal interface analogous to the SiO2/Si system by sulfurization.Insituphotoluminescence, measured during annealing in a phosphorous ambient in a mass spectrometer equipped low‐pressure chemical vapor deposition growth chamber, shows that surface degradation may be retarded by appropriate use of gaseous phosphorous. A phosphorous‐rich interfacial oxide, grown prior to SiO2growth, similarly appears to considerably improve the interface of InP metal–insulator–semiconductor (MIS) structures as seen byC–Vanalysis. Sulfurized InP MIS structures treated in (NH4)2Sx, show excellent interface quality as judged by high‐frequency and quasistaticC–Vmeasurements. MIS field effect transistors fabricated using the benefits of these surface treatments show large transconductances and stabilities approaching those of thermal SiO2/Si with<5% variation in drain current over a 12 h test period.

ISSN:1071-1023    

DOI:10.1116/1.584274

出版商:American Vacuum Society    

年代:1988

数据来源: AIP