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21 Aug 1995

Volume 67, Issue 8, pp. 1045-1171

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Wet chemical etching of AlN

J. R. Mileham, S. J. Pearton, C. R. Abernathy, J. D. MacKenzie, R. J. Shul, and S. P. Kilcoyne

Appl. Phys. Lett. 67, 1119 (1995); http://dx.doi.org/10.1063/1.114980 (3 pages) | Cited 60 times

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Single‐crystal AlN grown on Al2O3 is found to be wet etched by AZ400K photoresist developer solution, in which the active component is KOH. The etching is thermally activated with an activation energy of 15.5±0.4 kcal mol−1, and the etch rate is found to be strongly dependent on the crystalline quality of the AlN. There was no dependence of etch rate on solution agitation or any crystallographic dependence noted, and the etching is selective over other binary group III nitrides (GaN, InN) and substrate materials such as Al2O3 and GaAs. © 1995 American Institute of Physics.
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81.65.-b Surface treatments

Be incorporation and surface morphologies in homoepitaxial InP films

M. A. Cotta, M. M. G. de Carvalho, M. A. A. Pudenzi, K. M. I. Landers, C. F. de Souza, R. Landers, and O. Teschke

Appl. Phys. Lett. 67, 1122 (1995); http://dx.doi.org/10.1063/1.114981 (3 pages) | Cited 1 time

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We have studied the mechanism of Be incorporation in InP homoepitaxial films grown by metalorganic molecular beam epitaxy. The actual Be concentration in the films reaches 1–2×1019 cm−3 while the hole concentration saturates at a lower value ☒∼2×1018 cm−3 in our case). The measured lattice mismatch between film and substrate depends both on growth temperature and Be flux. The resulting changes in morphology suggest that the excess Be forms microclusters in the films grown at higher temperatures—due to the higher surface mobility, leading to the growth of oval defects. Be rejection to the surface is also observed. The surfaces of samples with no cap layer present a granulation which may be related to the formation of a new phase like Be3P2. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Theoretical analysis of the geometries of the luminescent regions in porous silicon

Nicola A. Hill and K. Birgitta Whaley

Appl. Phys. Lett. 67, 1125 (1995); http://dx.doi.org/10.1063/1.114982 (3 pages) | Cited 8 times

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The luminescence energies of a variety of crystalline silicon nanostructures are calculated using a time‐dependent tight‐binding technique. The calculated energies are compared with measured values for porous silicon samples to determine the geometries of the regions in which electron‐hole recombination occurs. We observe a correlation between luminescence wavelength and nanostructure which is consistent with the porosity changes during the etching process. We conclude that porous silicon samples which emit visible light are composed of small crystallites, and that the active regions in longer wavelength emitters are wirelike structures. © 1995 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Metalorganic chemical vapor deposition of tantalum nitride by tertbutylimidotris(diethylamido)tantalum for advanced metallization

M. H. Tsai, S. C. Sun, H. T. Chiu, C. E. Tsai, and S. H. Chuang

Appl. Phys. Lett. 67, 1128 (1995); http://dx.doi.org/10.1063/1.114983 (3 pages) | Cited 36 times

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We deposited tantalum nitride (TaN) films by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) using a new precursor tertbutylimidotris(diethylamido)tantalum (TBTDET). Strong Ta–N double bond in the precursor preserved the ‘‘TaN’’ portion during the pyrolysis process. This method has yielded low‐resistivity films. It changed from 10 mΩ cm (deposited at 500 °C) to 920 μΩ cm (obtained at 650 °C). The carbon and oxygen concentrations were low in the films deposited at 600 °C, as determined by x‐ray photoelectron spectroscopy. Transmission electron microscopy and x‐ray diffraction analysis indicated that the as‐deposited films exhibited polycrystalline structures with the lattice constants close to the bulk TaN value. The TaN barrier layer was successfully applied as a glue layer for CVD tungsten (W) metallization schemes. © 1995 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Deep levels caused by misfit dislocations in GaAsSb/GaAs heterostructures

T. Wosiński, A. Makosa, T. Figielski, and J. Raczyńska

Appl. Phys. Lett. 67, 1131 (1995); http://dx.doi.org/10.1063/1.114984 (3 pages) | Cited 9 times

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Two deep electron traps induced by lattice mismatch in relaxed GaAs1−xSbx layers (x=0% to 3%) grown by liquid phase epitaxy (LPE) on GaAs substrates have been revealed by means of deep‐level transient spectroscopy. One of the traps, that shows nonstandard, logarithmic capture kinetics and whose energy level is tied to the valence‐band edge, has been related to electron states associated with α dislocations. The other trap has been attributed to the EL2 defect and possible reasons of its unexpected formation in the LPE‐grown layers are briefly discussed. © 1995 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ultrathin luminescent nanoporous silicon on n‐Si: pH dependent preparation in aqueous NH4F solutions

Th. Dittrich, S. Rauscher, V. Yu. Timoshenko, J. Rappich, I. Sieber, H. Flietner, and H. J. Lewerenz

Appl. Phys. Lett. 67, 1134 (1995); http://dx.doi.org/10.1063/1.114985 (3 pages) | Cited 5 times

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Thin nanoporous Si layers were formed on n‐Si(100) in 0.1 M NH4F electrolyte and investigated with field emission scanning electron microscopy and photoluminescence (PL). The microstructure of the electrochemically prepared Si surfaces depended strongly on the pH of the electrolyte. A pebblelike surface structure was formed during anodization at pH 4.5, while nanoporous Si layers were formed at lower pH. The onset of macropore formation was observed after anodization at pH 3.0. The shape of the PL spectra was found to be practically independent of the nanoporous structure. The results are discussed on the basis of the etch rate of oxidized Si atoms and of the role of surface states for PL. © 1995 American Institute of Physics.  
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78.55.Hx Other solid inorganic materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Two dimensional electronic flute

M. I. Dyakonov and M. S. Shur

Appl. Phys. Lett. 67, 1137 (1995); http://dx.doi.org/10.1063/1.114986 (3 pages) | Cited 8 times

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Based on a complete similarity between the plasma waves in a field effect transistor and sound waves, we discuss a possibility of realizing an electronic terahertz oscillator utilizing the excitation of the plasma waves in the two dimensional resonance cavities by adjacent electron flow. © 1995 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
72.30.+q High-frequency effects; plasma effects

Photoluminescence of residual transition metal impurities in GaN

J. Baur, U. Kaufmann, M. Kunzer, J. Schneider, H. Amano, I. Akasaki, T. Detchprohm, and K. Hiramatsu

Appl. Phys. Lett. 67, 1140 (1995); http://dx.doi.org/10.1063/1.114987 (3 pages) | Cited 32 times

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A large number of epitaxial GaN samples as well as AlN ceramics have been studied by photoluminescence (PL) and PL excitation spectroscopy. In addition to the PL of residual iron, two new bands with zero‐phonon‐lines at 0.931 and 1.193 eV have been observed frequently in GaN. An analysis of the PL bands indicates that they arise from internal transitions within the 3d shell of residual vanadium and chromium impurities. The chromium PL has also been observed in polycrystalline AlN ceramics. © 1995 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors

Strain compensation in Si1−xGex by heavy boron doping

B. Tillack, P. Zaumseil, G. Morgenstern, D. Krüger, and G. Ritter

Appl. Phys. Lett. 67, 1143 (1995); http://dx.doi.org/10.1063/1.114988 (2 pages) | Cited 11 times

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Strain compensation in SiGe by heavy boron doping was demonstrated. For this purpose, SiGe layers containing up to several percent of boron were deposited using rapid thermal chemical vapor deposition. The strain compensation effect was evaluated by double crystal x‐ray diffraction measuring the difference between the diffraction peak distances of the boron doped samples and a reference sample without boron which can be directly related to the decrease of the lattice constant in Si1−x−yGexBy due to the incorporation of boron. The films were characterized by cross‐sectional transmission electron microscopy (XTEM), Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS). © 1995 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Superconducting and structural properties of in‐plane aligned a‐axis oriented YBa2Cu3O7−x thin films

Gun Yong Sung and Jeong Dae Suh

Appl. Phys. Lett. 67, 1145 (1995); http://dx.doi.org/10.1063/1.114989 (3 pages) | Cited 12 times

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We report the superconducting and structural properties of a‐axis oriented YBa2Cu3O7−x (YBCO) films as a function of deposition temperature of PrBa2Cu3O7−x (PBCO) template layers. X‐ray diffraction (XRD) analysis revealed the orientation relationship in which the b axis of the PBCO template layers and the a axis of the YBCO films were normal to the LaSrGaO4 (100) substrate surface. In‐plane aligned a‐axis oriented YBCO films having a zero resistance temperature of 88 K and an anisotropy ratio of resistivity of 11.5 at 275 K were obtained on PBCO template layers deposited at 630 °C among the deposition temperatures ranging from 600 to 650 °C at intervals of 10 °C. The degree of in‐plane alignment of the a‐axis oriented YBCO films which was estimated by the ratio of relative intensity at 90° and 180° in the XRD ϕ scan of the (102) YBCO peak was 0.5, 0.045, and 0.053 for the films on PBCO templates deposited at 620, 630, and 640 °C, respectively. In conclusion, the deposition temperature of PBCO template layers is critical to fabricate the in‐plane aligned a‐axis oriented YBCO films on LaSrGaO4 (100) substrates. © 1995 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
74.25.F- Transport properties

Epitaxial planarization of patterned yttria‐stabilized zirconia substrates for multilayer structures

Bertha P. Chang, Neville Sonnenberg, Michael J. Cima, Jonathan Z. Sun, and Lock See Yu‐Jahnes

Appl. Phys. Lett. 67, 1148 (1995); http://dx.doi.org/10.1063/1.114990 (3 pages) | Cited 1 time

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In situ planarization of epitaxial films has been demonstrated. This is a critical technology for the processing of any epitaxial multilayer device. Ion beam assisted deposition (IBAD) has been used to planarize patterned yttria‐stabilized ZrO2 (YSZ)(001) substrates using YSZ films. X‐ray diffraction measurements have shown that the IBAD YSZ grows homoepitaxially. The IBAD planarization mechanism has similarities to those previously observed for rf bias sputtering. Critical current densities of up to 7×105 A/cm2 at 77 K have been measured for Ba2YCu3O7−x (BYC) films deposited on planarized patterned YSZ substrates using pulsed laser deposition. In contrast, BYC deposited on unplanarized patterned YSZ substrates did not become fully superconducting for measurements down to 25 K. © 1995 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
74.78.-w Superconducting films and low-dimensional structures

Quantum well states in Ni/Cu/Ni spin valve structures

F. J. Himpsel and O. Rader

Appl. Phys. Lett. 67, 1151 (1995); http://dx.doi.org/10.1063/1.114991 (3 pages) | Cited 17 times

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Quantized states are mapped in Ni/Cu/Ni(100) trilayer structures, which are taken as a more accurate rendering of spin valve devices than the bilayers studied previously. We find that an extra Ni overlayer affects the energy of quantized states in the Cu layer, explaining why the magnetic coupling is affected by the thickness of the magnetic layer, and how a phase difference may occur between magnetic coupling oscillations in trilayers and density of states oscillations in bilayers. The potential step that confines electrons to the Cu spacer is determined to be 0.9 eV. © 1995 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Magnetostatically induced giant magnetoresistance in patterned NiFe/Ag multilayer thin films

T. L. Hylton, M. A. Parker, K. R. Coffey, J. K. Howard, R. Fontana, and C. Tsang

Appl. Phys. Lett. 67, 1154 (1995); http://dx.doi.org/10.1063/1.114992 (3 pages) | Cited 18 times

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Thin film multilayer structures consisting of two permalloy layers separated by Ag spacers show little or no giant magnetoresistance in their as‐deposited state, due to a predominantly ferromagnetic interlayer exchange coupling that does not oscillate in sign with variations in the Ag spacer thickness. Upon patterning these films into arrays of dots and other geometries with micron scale features, however, antiferromagnetic coupling and giant magnetoresistance are observed due to magnetostatic interactions between layers that are induced at the edges of the patterns. In this letter we present our experimental results and discuss their relevance as magnetoresistive sensors for magnetic recording heads and other applications. © 1995 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
85.70.-w Magnetic devices

Electron field emission from ion‐implanted diamond

W. Zhu, G. P. Kochanski, S. Jin, L. Seibles, D. C. Jacobson, M. McCormack, and A. E. White

Appl. Phys. Lett. 67, 1157 (1995); http://dx.doi.org/10.1063/1.114993 (3 pages) | Cited 106 times

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Diamond films and islands grown by chemical vapor deposition were implanted with boron, sodium, and carbon ions at doses of 1014–1015/cm2. This structural modification at the subsurface resulted in a significant reduction of the electric field required for electron emission. The threshold field for producing a current density of 10 mA/cm2 can be as low as 42 V/μm for the as‐implanted diamond compared to 164 V/μm for the high quality p‐type diamond. When the ion‐implanted samples were annealed at high temperatures in order to anneal out the implantation‐induced defects, the low‐field electron emission capability of diamond disappeared. These results further confirm our earlier findings about the role of defects in the electron emission from undoped or p‐type doped diamond and indicate that the improved emission characteristics of as‐implanted diamond is due to the defects created by the ion implantation process. © 1995 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.80.Jh Ion radiation effects

Microfabrication of a mechanically controllable break junction in silicon

C. Zhou, C. J. Muller, M. R. Deshpande, J. W. Sleight, and M. A. Reed

Appl. Phys. Lett. 67, 1160 (1995); http://dx.doi.org/10.1063/1.114994 (3 pages) | Cited 58 times

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We present a detailed description of the fabrication and operation at room temperature of a novel type of tunnel displacement transducer. Instead of a feedback system it relies on a large reduction factor assuring an inherently stable device. Stability measurements in the tunnel regime infer an electrode stability within 3 pm in a 1 kHz bandwidth. In the contact regime the conductance takes on a discrete number of values when the constriction is reduced atom by atom. This reflects the conduction through discrete channels. © 1995 American Institute of Physics.
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73.40.Jn Metal-to-metal contacts
73.40.Gk Tunneling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Scanning tunneling microscopy based lithography employing amorphous hydrogenated carbon as a high resolution resist mask

K. Kragler, E. Günther, R. Leuschner, G. Falk, A. Hammerschmidt, H. von Seggern, and G. Saemann–Ischenko

Appl. Phys. Lett. 67, 1163 (1995); http://dx.doi.org/10.1063/1.114995 (3 pages) | Cited 12 times

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Amorphous hydrogenated carbon (a–C:H) is introduced as a constituent of a two–layer resist system for lithography with a scanning tunneling microscope (STM) operating in air. The resist is made up of a thin electron sensitive and chemically amplified top resist (≤50 nm) and a–C:H as a thick conducting and etchable bottom resist. In this setup the bottom resist acts as the counter electrode allowing in principle operation on insulating substrates. We show that it is possible to generate structures with high aspect ratios by transfering the developed top resist patterns by means of oxygen reactive ion etching (RIE) into the bottom resist and halogen RIE into silicon substrates. Linewidths between 100 and 50 nm have been observed in the bottom resist as well as in the substrates. © 1995 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
FREE

Comment on ‘‘Nanoscale InP islands embedded in InGaP’’ [Appl. Phys. Lett. 66, 361 (1995)]

W. Seifert, N. Carlsson, M.‐E. Pistol, and L. Samuelson

Appl. Phys. Lett. 67, 1166 (1995); http://dx.doi.org/10.1063/1.114996 (2 pages) | Cited 2 times

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78.55.Cr III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
FREE

Response to ‘‘Comment on ‘Nanoscale InP islands embedded in InGaP’ ’’ [Appl. Phys. Lett. 67, 1166 (1995)]

A. Kurtenbach, K. Eberl, and T. Shitara

Appl. Phys. Lett. 67, 1168 (1995); http://dx.doi.org/10.1063/1.114997 (2 pages)

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Abstract Unavailable
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78.55.Cr III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
FREE

Comment on ‘‘Use of quantum well superlattices to obtain high figure of merit from nonconventional thermoelectric materials’’ [Appl. Phys. Lett. 63, 3230 (1993)]

D. A. Broido and T. L. Reinecke

Appl. Phys. Lett. 67, 1170 (1995); http://dx.doi.org/10.1063/1.114998 (2 pages) | Cited 35 times

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73.50.Lw Thermoelectric effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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