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15 Jun 1993

Volume 73, Issue 12, pp. R1-8664

Page 2 of 4 Pages Previous Page Next Page | Jump to Page

Pressure‐induced rocksalt phase of aluminum nitride: A metastable structure at ambient condition

Qing Xia, Hui Xia, and Arthur L. Ruoff

J. Appl. Phys. 73, 8198 (1993); http://dx.doi.org/10.1063/1.353435 (3 pages) | Cited 65 times

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Energy‐dispersive x‐ray diffraction studies were carried out on the III‐V compound aluminum nitride to 65 GPa using a synchrotron x‐ray source. A pressure‐induced first‐order phase transition from a wurtzite structure to a rocksalt structure was observed. The first peaks of the high‐pressure phase appeared at 14 GPa. On further loading of the diamond anvil cell, the wurtzite peaks disappeared by 20 GPa. After unloading the cell to atmospheric pressure, the rocksalt structure persisted. The equilibrium transformation pressure lies on the interval 0–14 GPa.
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64.70.K- Solid-solid transitions
81.40.Vw Pressure treatment
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
64.30.-t Equations of state of specific substances

Kinetics of laser‐induced phase transitions in Ni‐Al alloys

O. Bostanjoglo and V. Penschke

J. Appl. Phys. 73, 8201 (1993); http://dx.doi.org/10.1063/1.353436 (5 pages) | Cited 5 times

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Time‐resolved transmission electron microscopy (TEM) was applied to study phase transitions in free‐standing Ni0.75Al0.25 films, induced by pulses from an Nd:YAG laser (20 ns, 532 nm). At fluences above 0.23 J/cm2 melting occurred within the laser pulse, the liquid was set into violent motion during 300 ns after melting, and the film solidified 1–2 μs later. The liquid motion was triggered by expansion of the melting film. Solidification proceeded by heterogeneous nucleation of crystals at the periphery of the laser molten spot and by centripetal growth of large plates with velocities 0.9–2.4 m/s, from which a supercooling of 2–20 K at the liquid/crystal interface is inferred. The final texture consisted of large γ and γ′ crystals plus fine‐grained Al precipitates. The dynamics were either continuously traced or intermediate stages were visualized by double‐frame TEM with exposure times of some 10 ns.
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64.70.D- Solid-liquid transitions
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Penetration profiles for fast grain‐boundary diffusion by the dissociative mechanism

Yu. M. Mishin and Chr. Herzig

J. Appl. Phys. 73, 8206 (1993); http://dx.doi.org/10.1063/1.353437 (9 pages) | Cited 8 times

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A modified variant of Fisher’s model is proposed to describe the recently discovered phenomenon of fast impurity diffusion along grain boundaries (GBs) in metals as follows, (i) The fast diffusion is assumed to occur by the dissociative mechanism. Depending on the lattice dislocation density ρ the bulk diffusion of the impurity around GBs is either vacancy controlled [if (Dt)1/2≪ρ−1/2] or interstitial controlled [if (DT)1/2≫ρ−1/2]. In the first case the effective bulk diffusivity D depends on the GB concentration whereas in the second case D=const. (ii) Fast diffusers strongly segregate to GBs. The GB saturation effect is taken into account by introducing McLean’s isotherm of GB segregation. The GB penetration profiles calculated from approximate analytical solutions of the model exhibit two parts: a near‐surface part caused by the GB saturation effect and a more deeply penetrating linear segregation part with a much smaller slope. The second part of the profile either shows strong downward curvature (vacancy‐controlled D) or demonstrates normal Fisher‐like behavior (interstitial‐controlled D). Methods of profile treatment for the determination of GB diffusion parameters are presented. Based on the present model the available experimental data are critically considered and ideas of future experiments are discussed.
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66.30.J- Diffusion of impurities
61.72.Mm Grain and twin boundaries

Boron diffusion through thin gate oxides: Influence of nitridation and effect on the Si/SiO2 interface electrical characteristics

D. Mathiot, A. Straboni, E. Andre, and P. Debenest

J. Appl. Phys. 73, 8215 (1993); http://dx.doi.org/10.1063/1.353438 (6 pages) | Cited 41 times

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The diffusion of boron in N2 ambient is studied by using p+ polysilicon metal‐oxide‐silicon structures annealed during times long enough to allow boron diffusion through the gate oxide, up to the underlying substrate. Assuming equilibrium segregation at the interfaces, the boron diffusivity in the oxide is calculated by numerically fitting the resulting profile in the substrate. It is found that B diffuses in SiO2 with an activation energy of about 3 eV. We also quantify the influence of the nitridation of the oxide, and confirm its efficiency as a diffusion barrier. However, this study reveals a strong inconsistency between the extracted diffusivity values of B in SiO2 and the amount of B atoms being able to reach the Si/SiO2 interface to account for the observed interface state density.
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66.30.J- Diffusion of impurities
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.-b Surface treatments

Ion channeling study of Scx(Yb,Er)1−xAs films on GaAs (001)

A. Guivarc’h, Y. Ballini, M. Minier, B. Guenais, G. Dupas, G. Ropars, and A. Regreny

J. Appl. Phys. 73, 8221 (1993); http://dx.doi.org/10.1063/1.353439 (6 pages) | Cited 9 times

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1.8 MeV He+ ion backscattering and channeling was used to study various lattice matched and mismatched ScxYb1−xAs and ScyEr1−yAs films grown on GaAs (001). The lattice matching leads to excellent epitaxy with χmin as low as 1.5% along the [001] direction. It is demonstrated unambiguously that the interface peaks result from the first atoms of the Ga rows of the substrate, indicating that the As sublattice is continuous across the rare‐earth monoarsenide/GaAs interface. These lattice matched heterostructures are proposed as ideal tools for studying ion channeling phenomena. Concerning the mismatched heterostructures, it is shown that the mosaic resulting from the strain relaxation, and the lattice tilt occurring for thick films can be evaluated directly from aligned spectra.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Transmission electron microscopy and transmission electron diffraction structural studies of heteroepitaxial InAsySb1−y molecular‐beam epitaxial layers

Tae‐Yeon Seong, A. G. Norman, I. T. Ferguson, and G. R. Booker

J. Appl. Phys. 73, 8227 (1993); http://dx.doi.org/10.1063/1.353440 (10 pages) | Cited 19 times

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Molecular‐beam epitaxy InAsySb1−y layers were grown at temperatures ranging from 295 to 470 °C across the full composition range. Transmission electron microscopy and transmission electron diffraction (TED) examinations showed that for layers grown at and below 400 °C with nominal compositions 0.4<y<0.8, separation into two phases occurred resulting in a series of alternating plates approximately parallel to the layer surface. TED showed that the cubic lattices of the two phases were tetragonally distorted and their compositions were deduced to be typically InAs0.38Sb0.62 and InAs0.72Sb0.28. The plates were larger and more regular along the [110] direction than the [110] direction. As the growth temperature increased from 295 to 400 °C, for layers of nominal composition InAs0.5Sb0.5, the plate length increased from 0.1 to 2.0 μm and the plate thickness from 10 to 50 nm. Crystallographic defects were present in the layers and their occurrence was different in the phase‐separated and non‐phase‐separated layers. The plates formed spontaneously at the growing surface and were stable during subsequent annealing at 350 and 370 °C. It is suggested that they arise due to the presence of a miscibility gap at these growth temperatures. We have termed these spontaneously grown plate structures ‘‘natural’’ strained layer superlattices.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Doping of Si thin films by low‐temperature molecular beam epitaxy

H.‐J. Gossmann, F. C. Unterwald, and H. S. Luftman

J. Appl. Phys. 73, 8237 (1993); http://dx.doi.org/10.1063/1.353441 (5 pages) | Cited 67 times

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Two‐dimensional doping sheets (‘‘δ doping’’) are integral parts of many novel semiconductor device concepts. Deep submicron design rules require junction depths significantly below 100 nm. This level of control is difficult to achieve with ion implantation. We discuss the application of thermal, coevaporative doping with Sb and elemental B during Si molecular beam epitaxy at growth temperatures below ≊300 °C to this problem. We show that it is possible to create structures with very high doping levels, yet with very sharp doping transitions. Delta‐doping spikes with a full width at half maximum of <2.7 nm and <4.0 nm have been obtained by secondary‐ion mass spectrometry for Sb and B, respectively, with corresponding up‐slopes of 2.5 and 0.94 nm/decade. Homogeneously doped films show full activation up to NSb≊6×1020 cm−3 and NB≳1×1021 cm−3. Mobilities agree with bulk values at corresponding concentrations. Mesa‐isolated pn junctions exhibit ideality factors of 1.05.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si
73.61.Cw Elemental semiconductors

Pulsed laser deposition of SiC films on fused silica and sapphire substrates

L. Rimai, R. Ager, J. Hangas, E. M. Logothetis, Nayef Abu‐Ageel, and M. Aslam

J. Appl. Phys. 73, 8242 (1993); http://dx.doi.org/10.1063/1.353442 (8 pages) | Cited 10 times

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350‐nm‐wavelength laser ablation of ceramic SiC targets has been used to deposit SiC films on fused silica and R‐cut sapphire at substrate temperatures from 300 to 1150 °C. The films deposited above 800 °C show (111) and (222) x‐ray‐diffraction bands from crystal planes parallel to the substrate. The bandwidths decrease and the integrated intensities increase with deposition temperature. The crystallite dimension for the highest‐temperature films is in the order of 50 nm. The diffraction peaks are absent for the films deposited at the lower temperatures. Analysis of optical transmission spectra of the high‐temperature films shows a lowest‐energy gap near 2.2 eV which is the value for cubic SiC. The low‐temperature films show smaller and variable gaps. The room‐temperature resistivities of the former are low, from 0.02 to 0.1 Ω cm whereas the latter are insulating. Film thicknesses and deposition rates ranging from 0.2 to over 0.6 Å/pulse are obtained from the spectra and by monitoring of the interference oscillations in the infrared emission through the film during deposition.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
78.66.Li Other semiconductors

Single‐crystal Si/NiSi2/Si(100) structures

R. T. Tung, D. J. Eaglesham, F. Schrey, and J. P. Sullivan

J. Appl. Phys. 73, 8250 (1993); http://dx.doi.org/10.1063/1.353443 (8 pages) | Cited 1 time

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High‐quality, uniform, Si/NiSi2/Si(100) structures were demonstrated by a combination of molecular‐beam epitaxy and postgrowth, high‐temperature annealing. A Si template technique ensures the epitaxial orientation of the Si overlayer. The unusual inverse Volmer–Weber mode observed during the growth of Si on NiSi2(100) is shown to be a result of interface and surface energetics. The evolution of the interface morphology of the double‐heteroepitaxial structures is discussed in terms of thermodynamics.
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68.55.-a Thin film structure and morphology
68.35.Md Surface thermodynamics, surface energies

Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on (111)Si at low temperatures

T. L. Lee and L. J. Chen

J. Appl. Phys. 73, 8258 (1993); http://dx.doi.org/10.1063/1.353444 (9 pages) | Cited 14 times

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Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures have been studied by both conventional and high‐resolution transmission electron microscopy, Auger electron spectroscopy, and x‐ray diffraction. A 10‐nm‐thick yttrium thin film, deposited onto (111)Si at room temperature, was found to completely intermix with Si to form an 11‐nm‐thick amorphous interlayer. Crystalline Y5Si3 and Si were observed to nucleate first within the amorphous interlayer in samples annealed at temperatures lower than 200 °C. Epitaxial YSi2−x was found to be the only phase formed at the interface of amorphous interlayer and crystalline Si in samples annealed at temperatures higher than 250 °C. In as deposited 20‐ to 60‐nm‐thick Y thin films on silicon samples, crystalline Y5Si3, Si, and YSi and a 2.5‐nm‐thick amorphous layer were found to be present simultaneously. Good correlations were found among difference in atomic size between metal and Si atoms, the calculated free energy of mixing as well as the critical and maximum amorphous interlayer thickness for the Y/Si and a number of refractory metal/Si systems. The Y/Si system is the only system found up to date among all metal/Si systems that the a interlayer can be grown to a thickness exceeding 10 nm during deposition at room temperature.
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68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Misfit dislocation distributions in capped (buried) strained semiconductor layers

T. J. Gosling, R. Bullough, S. C. Jain, and J. R. Willis

J. Appl. Phys. 73, 8267 (1993); http://dx.doi.org/10.1063/1.353445 (12 pages) | Cited 31 times

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An elastic continuum model is used to investigate distributions of misfit dislocations in a capped layer structure. Effects of the free surface at the top of the cap and of interactions between dislocations have been rigorously incorporated, making the study applicable to structures with caps of arbitrary thickness and to the process of strain relaxation in layers already containing misfit dislocations. Two dislocation types are considered in detail: single dislocations (singles) residing at the lower interface, between the strained layer and the substrate, and dislocation dipoles, i.e., pairs of parallel dislocations with opposite Burgers vectors, one at the lower interface and the other at the upper interface, between the strained layer and the cap. Although singles cause unwanted long‐range distortion in the cap, which is not caused by dipoles, dipoles give rise to increased localised distortion, due to the presence of the additional dislocation, at the upper interface. Hence singles and dipoles compete as misfit dislocation types in capped layers, with the dominant type being determined by the parameters of the layer structure. It is demonstrated that interactions between dislocations are crucial, and that experimental observations cannot be explained by consideration of an isolated single or dipole. Interactions between singles in an array at the lower interface result in a buildup of strain energy in the cap. The rapidity of this buildup with dislocation density demands a transition from relaxation by singles to relaxation by arrays of dipoles; such a transition would not be predicted by a consideration of isolated singles or dipoles. Energy evaluations are performed to incorporate such interactions between dislocations while providing a sequential view of strain relaxation, with singles and dipoles entering the structure one at a time. It is thus demonstrated that a mixture of singles and dipoles is expected in many capped layers of practical interest. An example calculation predicts a mixture that is consistent with experimental observation.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Lk Linear defects: dislocations, disclinations

Silicide formation and silicide‐mediated crystallization of nickel‐implanted amorphous silicon thin films

C. Hayzelden and J. L. Batstone

J. Appl. Phys. 73, 8279 (1993); http://dx.doi.org/10.1063/1.353446 (11 pages) | Cited 185 times

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The nucleation and growth of isolated nickel disilicide precipitates in Ni‐implanted amorphous Si thin films and the subsequent low‐temperature silicide‐mediated crystallization of Si was studied using in situ transmission electron microscopy. Analysis of the spatial distribution of the NiSi2 precipitates strongly suggested the occurrence of site saturation during nucleation. NiSi2 precipitates were observed in situ to migrate through the amorphous Si thin films leaving a trail of crystalline Si at temperatures as low as ∼484 °C. Initially, a thin region of epitaxial Si formed on {111} faces of the octahedral NiSi2 precipitates with a coherent interface which was shown by high‐resolution electron microscopy to be Type A. Migration of the NiSi2 precipitates led to the growth of needles of Si which were parallel to 〈111〉 directions. The growth rate of the crystalline Si was limited by diffusion through the NiSi2 precipitates, and an effective diffusivity was determined at 507 and 660 °C. A mechanism for the enhanced growth rate of crystalline Si is proposed.
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81.15.Np Solid phase epitaxy; growth from solid phases
61.72.uf Ge and Si
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Incongruent transfer in laser deposition of FeSiGaRu thin films

E. van de Riet, J. C. S. Kools, and J. Dieleman

J. Appl. Phys. 73, 8290 (1993); http://dx.doi.org/10.1063/1.353447 (7 pages) | Cited 32 times

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The laser ablation and deposition of FeSiGaRu is studied. The deposited thin films are analyzed with Auger electron spectroscopy and Rutherford backscattering spectrometry. It is found that the gallium and ruthenium content of the thin films is strongly dependent on the laser fluence. At high laser fluences (6 J/cm2) the thin films are depleted of gallium due to preferential sputtering of the gallium atoms from the thin film. Near the threshold fluence (1.9 J/cm2) the films contain an excess of gallium due to preferential evaporation of gallium from the target. The latter conclusions are based on time‐of‐flight studies of ablated atoms and ions and on measurements of the atoms that are sputtered from the substrate by the incoming flux.
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68.55.Nq Composition and phase identification
81.15.Fg Pulsed laser ablation deposition
75.50.Bb Fe and its alloys

The energetics of dislocation array stability in strained epitaxial layers

T. J. Gosling, J. R. Willis, R. Bullough, and S. C. Jain

J. Appl. Phys. 73, 8297 (1993); http://dx.doi.org/10.1063/1.354087 (7 pages) | Cited 15 times

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Two aspects of the energetics of dislocation array stability in lattice‐mismatched strained layers are addressed. The first concerns criteria for determining equilibrium dislocation distributions in strained layers; the second concerns the difference between the energies of arrays of dislocations in which the Burgers vectors of all dislocations are identical, and those in which the screw components of the Burgers vectors alternate. The conclusions reached are at variance with those of recent work by Feng and Hirth on periodic arrays of dipoles in an infinite body [X. Feng and J. P. Hirth, J. Appl. Phys. 72, 1386 (1992); J. P. Hirth and X. Feng, J. Appl. Phys. 67, 3343 (1990)]. In particular, it is emphasized that if layers remain in equilibrium then there is always a residual mean strain; in other words, the mismatch strain is never completely relaxed. Also it is shown, via a direct calculation, that although alternating the screw components of the Burgers vectors of dislocations within a single array is energetically favorable, it is preferable to have all screw components of the same sign within an array if two orthogonal arrays are considered. Although for comparison with the work of Feng and Hirth arrays of dipoles in an infinite body are considered in more detail, the stated conclusions are also shown to hold for arrays of unpaired dislocations near a free surface.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Lk Linear defects: dislocations, disclinations

Optimal epilayer thickness for InxGa1−xAs and InyAl1−yAs composition measurement by high‐resolution x‐ray diffraction

Brian R. Bennett and Jesús A. del Alamo

J. Appl. Phys. 73, 8304 (1993); http://dx.doi.org/10.1063/1.353448 (5 pages) | Cited 11 times

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The composition of InxGa1−xAs and InyAl1−yAs epitaxial layers on InP substrates can be measured by high‐resolution x‐ray diffraction (HRXRD) in many cases. If layers are too thick, however, substantial lattice relaxation will occur, requiring multiple asymmetric scans to determine composition. If layers are too thin, they will not produce a distinct Bragg peak. Based upon measurements of both coherent and relaxed layers as well as simulations, we have determined the range of epilayer thickness over which a single HRXRD scan yields the composition of InxGa1−xAs and InyAl1−yAs layers to within 1%. Calibration layers grown within this range allow fast and accurate characterization.
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68.55.Nq Composition and phase identification
61.05.C- X-ray diffraction and scattering

Hindered transformation of Pd2Ge to PdGe in the Pd/a‐Ge:H system

F. Edelman, C. Cytermann, R. Brener, M. Eizenberg, R. Weil, and W. Beyer

J. Appl. Phys. 73, 8309 (1993); http://dx.doi.org/10.1063/1.353449 (4 pages)

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A comparative study of the interfacial reactions between Pd and a‐Ge:H, deposited at TS=150 °C (low temperature, LT) and at TS=200, 300 °C (high temperature, HT), was carried out by x‐ray diffraction and Auger electron spectroscopy after sample annealing in the regime of T=200–300 °C and t=1/4–4 h. It was found that the Pd/a‐Ge:H(LT) formed a much more stable Pd2Ge interfacial layer, compared to the Pd/a‐Ge:H(HT) system in which the Pd2Ge was transformed to PdGe. The main difference between the LT‐ and the HT‐a‐Ge:H films is probably the structure of the material. Whereas the HT films are compact, the LT‐a‐Ge films contain a network of voids which slow down the diffusion of Ge to the interface.
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68.35.Fx Diffusion; interface formation
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.Nq Composition and phase identification

Remote n‐type modulation doping of InAs quantum wells by ‘‘deep acceptors’’ in AlSb

Jun Shen, John D. Dow, Shang Yuan Ren, Saied Tehrani, and Herb Goronkin

J. Appl. Phys. 73, 8313 (1993); http://dx.doi.org/10.1063/1.353450 (6 pages) | Cited 15 times

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Due to the fact that impurities normally change their doping characters when they undergo shallow to deep transitions or deep‐to‐false‐valence transitions, a single defect, such as a cation on an Sb site, can explain all of the following facts for nonintentionally doped AlxGa1−xSb alloys and InAs/AlxGa1−xSb superlattices and quantum‐well structures: (i) Bulk GaSb is p type; (ii) bulk AlSb is semi‐insulating; (iii) InAs/AlSb superlattices with InAs quantum wells thicker than a critical thickness dc(x=1.0) are n type, where the InAs shallow–deep critical thickness function dc(x) is around ≂100–≂150 Å for 0.5<x≤1.0 for InAs/AlxGa1−xSb superlattices; (iv) InAs/AlSb superlattices with InAs quantum wells thinner than dc(x=1.0) are semi‐insulating. In addition, the theory predicts that Al0.5Ga0.5Sb and AlSb will be semi‐insulating when nonintentionally doped, but can be converted to p type by the application of hydrostatic pressure P: P≳90 kbar and P≳150 kbar, respectively. These changes of doping character, which lie outside the conventional effective‐mass theory, occur often in type‐II band‐alignment systems, such as InAs/AlxGa1−xSb.  
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors

Free‐carrier absorption of nondegenerate semiconductors in quantizing magnetic fields: Nonpolar optical phonon scattering

Chhi‐Chong Wu and Chau‐Jy Lin

J. Appl. Phys. 73, 8319 (1993); http://dx.doi.org/10.1063/1.353423 (5 pages) | Cited 1 time

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The effect of nonpolar optical phonon scattering on the free‐carrier absorption in n‐type semiconductors such as germanium has been investigated quantum mechanically in quantizing magnetic fields. It is assumed that the energy band structure of electrons in semiconductors is nonparabolic and the dominant scattering mechanism for conduction electrons is of the nonpolar optical phonon scattering. When the radiation is polarized parallel to a dc magnetic field B, the absorption coefficient appears to be of a complex value due to the interaction between the radiation field and the optical phonon field in nondegenerate semiconductors. Results show that the real part of the absorption coefficient oscillates with the magnetic field in the high‐field region, and imaginary part of the absorption coefficient appears with a few extremum points (peaks and dips) in high magnetic fields. These are different from those of the acoustic phonon scattering in III–V compound semiconductors such as InSb or GaAs, in which the absorption coefficient oscillates with the magnetic field in lower magnetic fields and then increases monotonically with the field.  
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72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
78.20.-e Optical properties of bulk materials and thin films
72.20.My Galvanomagnetic and other magnetotransport effects

Multicarrier characterization method for extracting mobilities and carrier densities of semiconductors from variable magnetic field measurements

J. S. Kim, D. G. Seiler, and W. F. Tseng

J. Appl. Phys. 73, 8324 (1993); http://dx.doi.org/10.1063/1.353424 (12 pages) | Cited 43 times

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A simple, practical method is described to extract the carrier concentration and mobility of each component of a multicarrier semiconductor system (which may be either a homogeneous or multilayered structure) from variable magnetic field measurements. Advantages of the present method are mainly due to the inclusion of both the longitudinal and transverse components of the conductivity tensor and normalization of these quantities with respect to the zero‐field longitudinal component of the conductivity tensor. This method also provides a simple, direct criterion by which one can easily determine whether the material under test is associated with a one‐carrier or multicarrier conduction. The method is demonstrated for a simple one‐carrier system [GaAs single‐channel high‐electron‐mobility‐transistor (HEMT) structure] and two multicarrier systems (an InGaAs‐GaAs double‐channel HEMT structure and two types of carriers present in an InGaAs single‐channel HEMT structure). The analysis of the experimental data obtained on these samples demonstrates the utility of the method presented here for extracting carrier concentrations and mobilities in advanced semiconductor structures.
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72.20.-i Conductivity phenomena in semiconductors and insulators
73.50.-h Electronic transport phenomena in thin films

Nondestructive diagnostic method using ac surface photovoltage for detecting metallic contaminants in silicon wafers

Hirofumi Shimizu and Chusuke Munakata

J. Appl. Phys. 73, 8336 (1993); http://dx.doi.org/10.1063/1.353425 (4 pages) | Cited 18 times

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Effects of residual metal impurities after RCA (Radio Corporation of America) standard cleaning (alkaline and acid rinses) on the generation of ac surface photovoltages (SPVs) are investigated using n‐type silicon wafers. Aluminum (Al) and iron (Fe) in the native oxide induce a negative charge, causing high ac SPVs in n‐type wafers. The ac SPV dependency on the concentration of Al and Fe is determined. Nickel and zinc, however, have little effect on the generation of ac SPVs. In commonly employed cleaning processes, Al is the major impurity in the native oxide, and thus the ac SPV technique is applicable to nondestructive diagnostics for quality control in cleaning processes.
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72.40.+w Photoconduction and photovoltaic effects
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Behavior of InP:Fe under high electric field

K. Turki, G. Picoli, and J. E. Viallet

J. Appl. Phys. 73, 8340 (1993); http://dx.doi.org/10.1063/1.353426 (9 pages) | Cited 9 times

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The behavior of semi‐insulating InP:Fe under high electric field is investigated. The current‐voltage (I‐V) characteristics are studied on both long liquid‐encapsulated Czochralski‐grown samples and short epitaxial‐grown layers. These characteristics show a linear regime at low voltages followed, for higher voltages, by a nonlinear behavior and a current breakdown. The critical electric field at which the nonlinearity begins is found to be independent of the sample thickness, the material compensation, and the nature of the contacts, and is equal to 10 kV/cm. This fact rules out the usual explanation in terms of Lampert’s injection theory. In the nonlinear regime, a slow transient response (≊1 s at room temperature) is observed only for long samples. The time constant of this effect exhibits a thermal activation energy (≊0.64 eV) close to that of the iron‐related deep level. Field‐dependent effects on the thermal emission rate and the capture cross section are discussed. Considering a field enhancement of the capture cross section, we propose a model to explain both the nonlinear characteristics and the slow dynamic behavior of long samples. The current breakdown observed at higher fields is attributed to an impact ionization of the deep levels and not to a trap‐filled‐limit voltage as previously reported.
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72.20.Ht High-field and nonlinear effects
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Energy levels of GaSb grown by metalorganic chemical vapor deposition

Y. K. Su and S. M. Chen

J. Appl. Phys. 73, 8349 (1993); http://dx.doi.org/10.1063/1.353427 (4 pages) | Cited 8 times

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Undoped GaSb epilayers were grown on GaSb and GaAs substrates using the metalorganic chemical vapor deposition (MOCVD) technique, and photoluminescence (PL). Hall effect measurements were used to characterize the undoped epilayers. For undoped GaSb epilayers, four energy levels revealed by PL spectra are shown to be due to acceptors, using KTdp/dEf va Ef‐Ev data obtained from Hall effect results, where p is the hole concentration, Ef and Ev are the Fermi level and the top of valence band, respectively. The acceptor levels lie at 3, 58, 80, and 130 meV above the top of valence band, respectively. The donor level is 15 meV below the bottom of the conduction band. These acceptor levels exist in almost all of the undoped p‐type GaSb epilayers grown at high temperature, while the donor level exists only in the undoped n‐type GaSb epilayers grown by low‐temperature MOCVD. It is found that these levels may be changed using the different growth temperatures.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Trap‐assisted conduction in nitrided‐oxide and re‐oxidized nitrided‐oxide n‐channel metal‐oxide‐semiconductor field‐effect transistors

S. Fleischer, P. T. Lai, and Y. C. Cheng

J. Appl. Phys. 73, 8353 (1993); http://dx.doi.org/10.1063/1.354086 (6 pages) | Cited 8 times

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The off‐state leakage characteristics of n‐channel metal‐oxide‐semiconductor field‐effect transistors with pure oxide, low‐partial pressure nitrided (LPN) oxide, re‐oxidized LPN, and nitrogen‐annealed LPN oxide as the gate insulator, were investigated over the temperature range 300–400 K. In the high‐field region (above 7 MV/cm), the gate‐induced drain leakage was found to be due to band‐to‐band tunneling for all samples. Low‐field conduction was determined to be due to a gate current which was many orders of magnitude higher than the Fowler–Nordheim current observed in capacitors on the same wafers. A trap‐assisted tunneling model was employed, using a trap energy of 0.7 eV determined from the activation data, in order to explain the low‐field gate current. The most likely cause of this enhanced conduction is oxide degradation in the gate‐to‐drain overlap region created during the source/drain implant.
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73.40.Gk Tunneling
85.30.Tv Field effect devices
73.61.Ng Insulators

Transport measurements in p‐type CdTe single crystals and ion‐beam doped thin films

Jochen Moesslein, Adolfo Lopez‐Otero, Alan L. Fahrenbruch, Donghwan Kim, and Richard H. Bube

J. Appl. Phys. 73, 8359 (1993); http://dx.doi.org/10.1063/1.353428 (5 pages) | Cited 4 times

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Electrical transport properties of phosphorus‐doped p‐type CdTe single crystals and phosphorus‐ion‐beam doped, homoepitaxial thin films have been investigated by means of van der Pauw Hall effect and resistivity measurements as a function of temperature from 8 to 400 K. Analysis of the data indicates a maximum doping level greater than 2×1017 cm−3 in the films, at least as high as in the single crystals. Phosphorus has an ionization energy of about 40 meV, the degree of compensation is smaller in the films, room temperature mobilities of the films are lower than those for single crystals by about 20%, and the temperature dependence of mobility is similar for both crystals and films. Impurity scattering is dominant at lower temperatures and polar mode scattering is dominant at higher temperatures with a maximum mobility at 150–190 K. Both the single crystals and the ion‐assisted doped films show a temperature independent resistivity at temperatures below 40 K, indicating the presence of impurity band conduction.
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72.80.Ey III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects

Fabrication of high mobility two‐dimensional electron and hole gases in GeSi/Si

Y. H. Xie, E. A. Fitzgerald, D. Monroe, P. J. Silverman, and G. P. Watson

J. Appl. Phys. 73, 8364 (1993); http://dx.doi.org/10.1063/1.353429 (7 pages) | Cited 56 times

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A procedure for the fabrication of two‐dimensional carrier (electron and hole) gases in modulation doped GeSi/Si heterostructures is presented. The best 4.2 K mobilities measured for the two‐dimensional electron and hole gases are 180 000 cm2/V s and 18 000 cm2/V s, respectively. Recently, two‐dimensional hole gases with mobilities as high as 55 000 cm2/V s have been obtained. The carrier gases are fabricated on top of relaxed, compositionally graded GexSi1−x buffer layers with low threading dislocation densities (≊106 cm−2). Experimental evidence indicates that the function of the graded buffer is to promote dislocation propagation while suppressing nucleation. A comparative analysis is carried out for two dimensional electron gases in GeSi/Si/GeSi and in AlGaAs/GaAs structures. Although molecular beam epitaxy is used to grow the samples, the principle discussed here is independent of growth technique.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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