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31 Aug 1992

Volume 61, Issue 9, pp. 1013-1139

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Cathodoluminescence imaging and spectroscopy of dislocations in Si and Si1−xGex alloys

V. Higgs, E. C. Lightowlers, S. Tajbakhsh, and P. J. Wright

Appl. Phys. Lett. 61, 1087 (1992); http://dx.doi.org/10.1063/1.107676 (3 pages) | Cited 25 times

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Dislocations in float‐zone Si which has been plastically deformed and deliberately copper contaminated, and misfit dislocations in a relaxed Si1−xGex alloy layer grown on a Si substrate by molecular beam epitaxy, have been investigated by monochromatic and panchromatic cathodoluminescence imaging and by cathodoluminescence spectroscopy. The measurements show that the D3 and D4 luminescence features originate on the slip lines in plastically deformed Si and at the misfit dislocations in the Si1−xGex alloy layer whereas the D1 and D2 bands are dominant between the slip lines and the misfit dislocations.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Dv Composition, segregation; defects and impurities
71.55.Ht Other nonmetals

Inhibition of etching in oxygen‐implanted AlGaAs

C. L. Reynolds, S. E. Lengle, R. E. Ahrens, and S. M. Parker

Appl. Phys. Lett. 61, 1090 (1992); http://dx.doi.org/10.1063/1.107677 (2 pages)

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Ion bombardment for the formation of thermally stable, high resistivity layers in GaAs and AlGaAs is well known. The impact of this device isolation scheme on subsequent processing steps is less understood. Here, we report on an inhibition of etching in oxygen‐implanted AlGaAs at an ion dose of 1×1014/cm2. Speculation on potential applications is given.  
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61.72.U- Doping and impurity implantation
61.80.Jh Ion radiation effects
81.65.-b Surface treatments

Improved performance of carbon‐doped GaAs base heterojunction bipolar transistors through the use of InGaP

C. R. Abernathy, F. Ren, P. W. Wisk, S. J. Pearton, and R. Esagui

Appl. Phys. Lett. 61, 1092 (1992); http://dx.doi.org/10.1063/1.107678 (3 pages) | Cited 23 times

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Carbon‐doped GaAs/AlGaAs heterojunction bipolar transistors (HBTs) typically exhibit severe leakage at the base‐emitter interface which limits their utility for low‐current applications. Furthermore, the device breakdown voltage, and hence power handling capability, is limited due to the band gap of the GaAs collector material. In this letter we will demonstrate for the first time that both of these limitations can be overcome through the use of InGaP. Since InGaP is not readily doped with carbon, it does not suffer from compensation due to carryover of carbon from the GaAs base. Hence, the ideality factor of the base‐emitter junction improves from 1.3 to 1.09 when the conventional n‐AlGaAs emitter layer is replaced with n‐InGaP. Moreover, InGaP eliminates the crossover of the base and collector currents typically observed in heavily carbon doped GaAs HBTs. This results in the maintenance of gain even at very low collector currents. As a collector material, we have found that InGaP produces significantly higher breakdown voltage than GaAs (19 V vs 12 V) of the same thickness and doping, due to its larger band gap. As in the emitter, InGaP collectors exhibit excellent ideality factors of ∼1.05.
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85.30.Pq Bipolar transistors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Low residual impurities assessment by photoluminescence in multistep wafer‐annealed semi‐insulating Czochralski‐grown GaAs

O. Ka, O. Oda, Y. Makita, and A. Yamada

Appl. Phys. Lett. 61, 1095 (1992); http://dx.doi.org/10.1063/1.107679 (3 pages) | Cited 5 times

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Multistep wafer‐annealed semi‐insulating GaAs wafers (MWA) are characterized using photoluminescence (PL). The PL spectra present well‐resolved near‐band‐edge transitions, including the doublet of the neutral acceptor‐bound exciton. A detailed investigation using selective pair luminescence of samples submitted to different annealings, i.e., wafer‐ or ingot‐annealing, single or multistep, shows that carbon is the main shallow acceptor. However, for the wafer‐annealed samples, two other residual impurities found in the as‐grown or ingot‐annealed crystals have their estimated concentrations noticeably reduced, for Zn (e.g., around 1013 cm−3 in MWA), or are unresolved for Si. This reduction of background impurities may have direct consequences for device applications.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
61.72.U- Doping and impurity implantation

Spectroscopic ellipsometric measurements of the dielectric function of germanium dioxide films on crystal germanium

Y. Z. Hu, J.‐Th. Zettler, S. Chongsawangvirod, Y. Q. Wang, and E. A. Irene

Appl. Phys. Lett. 61, 1098 (1992); http://dx.doi.org/10.1063/1.107680 (3 pages) | Cited 12 times

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From spectroscopic ellipsometry measurements in the 1.5–5.7 eV photon energy range we determined the complex dielectric function of thermally grown germanium dioxide in the 1.0–6.3 eV range. A Kramers–Kronig consistent dispersion formula utilizing an exponential‐shaped optical band edge was used in conjunction with both previously published far ultraviolet absorbance data for amorphous GeO2 and our spectra. These measurements show that ϵ2 for GeO2 can be regarded to be zero in the range of E<5.5 eV, which differs from a previous report. Using these new optical results for the investigation of oxide growth, we find that GeO2 grows via a parabolic growth law with a growth constant, kp=1.2×10−19 m2 s−1 at 550 °C.
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81.65.-b Surface treatments
78.66.-w Optical properties of specific thin films
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films

Interdiffusion problems at CdTe/InSb heterointerfaces grown by temperature gradient vapor transport deposition

T. W. Kim, M. Jung, H. L. Park, H. K. Na, and J. S. Kim

Appl. Phys. Lett. 61, 1101 (1992); http://dx.doi.org/10.1063/1.107681 (3 pages) | Cited 7 times

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CdTe epitaxial films were grown by a simple method of temperature gradient vapor transport deposition on p‐InSb (111) orientation substrates in the growth temperature range between 200 and 280 °C. Raman spectroscopy showed the optical phonon modes of the CdTe thin films and the formation of an indium telluride interfacial layer in the CdTe/InSb heterostructures. The stoichiometry of the CdTe/InSb heterostructures was observed by the Auger electron spectroscopy, and Auger depth profiles also demonstrated that the CdTe/InSb heterointerface was not abrupt. The results indicated that the films grown at about 265 °C posed a significant problem due to interdiffusion from the InSb substrates during the growth.
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68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
78.30.Fs III-V and II-VI semiconductors

Scanning tunneling microscopy of GaAs multiple pn junctions

S. Gwo, A. R. Smith, C. K. Shih, K. Sadra, and B. G. Streetman

Appl. Phys. Lett. 61, 1104 (1992); http://dx.doi.org/10.1063/1.107682 (3 pages) | Cited 20 times

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Scanning tunneling microscopy and spectroscopy is used to study GaAs multiple pn junction samples cleaved in ultrahigh vacuum. Direct topographic contrast over the pn junctions can be observed in the constant current imaging mode. The topographic height in the p‐type regions appears much lower (by about 5 Å) than that in the n‐type regions. Tunneling spectroscopy measurements show consistency with the assignment of the p‐ and n‐type regions. We discuss a possible mechanism for the observed contrast.
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07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states

Observation of interface traps in the silicon conduction band at the (100)Si/SiO2 interface at 4.2 K

W. R. Anderson, R. G. Wheeler, and T. P. Ma

Appl. Phys. Lett. 61, 1107 (1992); http://dx.doi.org/10.1063/1.107683 (3 pages)

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Measurement of the gate capacitance‐voltage and conductance‐voltage characteristics of metal‐oxide‐semiconductor field‐effect transistors at 4.2 K has been used to search for Si/SiO2 interface traps above the silicon conduction band edge. A distinct feature emerges in the gate conductance curves after x‐ray irradiation providing strong evidence for the formation of conduction‐band interface traps. Trap densities and time constants have been extracted using a distributed circuit model. The trap energy level lies about 20 meV above the bottom of the conduction band.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.De Semiconductor-device characterization, design, and modeling

Charge transfer and low‐temperature electron mobility in a strained Si layer in relaxed Si1−xGex

Frank Stern and Steven E. Laux

Appl. Phys. Lett. 61, 1110 (1992); http://dx.doi.org/10.1063/1.107684 (3 pages) | Cited 54 times

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Calculated results for charge transfer and low‐temperature electron mobility in strained silicon grown epitaxially on relaxed Si1−xGex are presented versus the thickness of an undoped spacer layer and other structural and materials parameters. The indicated conduction band offset for Si on relaxed Si0.7Ge0.3 is 180±15 meV. Scattering by the remote doping impurities that supply the carriers is found to be the dominant scattering mechanism in high‐mobility samples. Samples with enhanced interface scattering are expected to have a stronger temperature dependence of mobility.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Bk General theory, scattering mechanisms

Continuous coherent microwave oscillation in InSb p‐n junctions

Katsutoshi Kamakura

Appl. Phys. Lett. 61, 1113 (1992); http://dx.doi.org/10.1063/1.107685 (3 pages)

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Continuous coherent microwave oscillation is observed in InSb p‐n junctions under the application of a dc reverse bias voltage in the region of avalanche breakdown and an external high magnetic field at 77 K. The observed oscillation frequency varies with the sample current of the p‐n junction and the magnetic field. The oscillation mechanism seems to be different from that of impact‐avalanche transit‐time (IMPATT) diodes because the external high magnetic field is required to cause the microwave oscillation in the InSb p‐n junctions.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Composition dependent transport properties of strain relaxed InxGa1−xAs(x<0.45) epilayers

Jianhui Chen, J. M. Fernandez, and H. H. Wieder

Appl. Phys. Lett. 61, 1116 (1992); http://dx.doi.org/10.1063/1.107686 (3 pages) | Cited 9 times

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The concentration and mobility of the two‐dimensional electron gas present at the interface between strain‐relaxed, lattice matched, InyAl1−yAs/InxGa1−xAs(x < 0.45), modulation doped heterojunctions grown by means of compositionally step‐graded buffer layers on GaAs substrates, were measured at room temperature and at 77 K. The composition dependence of the electron density is attributed to the dependence of the band‐gap energy of InxGa1−xAs and that of InyAl1−yAs on x, with a conduction band offset, ΔEc∼0.67ΔEg. The room temperature electron mobility increases from 9×103 cm2/V s for x=0.07 to 1.05×104 cm2/V s for x=0.45. Such strain‐relaxed heterostructures have higher electron mobilities than similar pseudomorphic structures with the same sheet electron concentration.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Silver on diamond Schottky diodes formed on boron doped hot‐filament chemical vapor deposited polycrystalline diamond films

G. Zhao, T. Stacy, E. J. Charlson, E. M. Charlson, C. H. Chao, M. Hajsaid, J. Meese, G. Popovici, and M. Prelas

Appl. Phys. Lett. 61, 1119 (1992); http://dx.doi.org/10.1063/1.107687 (3 pages) | Cited 16 times

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Schottky diodes were fabricated using sputter deposited silver contacts to boron doped polycrystalline diamond thin films grown by a hot‐filament chemical vapor deposition process with trimethyl borate as an in situ dopant source. High forward current density and a high forward‐to‐reverse current ratio were exhibited by these diodes. Current density‐voltage and capacitance‐voltage‐frequency characteristics of these diodes are very similar to those of Schottky diodes fabricated using a single‐crystal diamond substrate.
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85.30.Hi Surface barrier, boundary, and point contact devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Ei Rectification

Broadband (8–14 μm), normal incidence, pseudomorphic GexSi1−x/Si strained‐layer infrared photodetector operating between 20 and 77 K

R. People, J. C. Bean, C. G. Bethea, S. K. Sputz, and L. J. Peticolas

Appl. Phys. Lett. 61, 1122 (1992); http://dx.doi.org/10.1063/1.107688 (3 pages) | Cited 46 times

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Performance characteristics of a pseudomorphic p‐type, normal incidence, Ge0.25Si0.75/Si strained‐layer quantum well infrared photodetector on (001) Si is described for 20≤T≤77 K. The device shows broadband photoresponse (8–14 μm) which is attributed to strain and quantum confinement induced mixing of heavy, light, and split‐off hole bands. Typical device responsivity at λ=10.8 μm is ∼0.04 A/W over the 20–77 K temperature range. A detectivity D∗λ=3.3×109 cm √Hz/W was measured at a bias of −2.4 V for a temperature of 77 K at λ=10.8 μm and no cold shield. Room temperature FTIR measurements yield a quantum efficiency η≊3.1% at λp≊8 μm at 300 K.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.De Semiconductor-device characterization, design, and modeling

Role of hydrogen in the growth of Y1Ba2Cu3O7 on MgO substrates by off‐axis magnetron sputtering

Edward J. Cukauskas, Laura H. Allen, Gregory K. Sherrill, and R. T. Holm

Appl. Phys. Lett. 61, 1125 (1992); http://dx.doi.org/10.1063/1.107689 (3 pages) | Cited 7 times

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Y1Ba2Cu3O7 thin films have been grown on MgO by off‐axis magnetron sputtering using mixtures of argon, oxygen, and hydrogen. Reduction in film transition temperature resulting from cumulative target sputtering time (target degradation) is minimized by adding hydrogen to the sputtering gas. Without hydrogen, new targets which had produced films with 87.5 K transition temperatures degraded with deposition time and produced films with transition temperatures of only 82 K. After addition of hydrogen, these targets produced films with transition temperatures of nearly 89 K. Critical‐current densities for the films made at optimum hydrogen flow were greater than 3×106 A/cm2 at 4 K. With the addition of hydrogen, we observed a significant increase in the sputtergun cathode voltage and a dramatic increase in the deposition rate. The films were predominantly c‐axis oriented, and we observed a minimum c‐axis lattice parameter for optimum hydrogen flow. We attribute these improvements in material properties to the catalytic effect of hydrogen in maintaining atomic oxygen in the plasma, allowing more oxygen to be incorporated into the target and the film during growth.
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81.15.Cd Deposition by sputtering
74.70.-b Superconducting materials other than cuprates

Characteristics of high performance YBa2Cu3O7 step‐edge junctions

J. Luine, J. Bulman, J. Burch, K. Daly, A. Lee, C. Pettiette‐Hall, S. Schwarzbek, and D. Miller

Appl. Phys. Lett. 61, 1128 (1992); http://dx.doi.org/10.1063/1.107690 (3 pages) | Cited 29 times

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Step‐edge Josephson junctions are engineered grain boundary junctions fabricated using standard lithographic and film deposition techniques. We report a systematic study of 180 YBa2Cu3O7 step‐edge junctions and identify a fabrication technique which results in a 90% yield of working junctions with critical current spreads from 30% to 50% (1σ/Ic‐ave)over the entire substrate. Technically useful critical current values at 65 K can be obtained by adjusting YBa2Cu3O7 film thickness. IcRn values, approximately independent of film thickness, are ∼1 mV at 4.2 K and ∼0.1 mV at 65 K. Most junctions exhibit ideal electrical behavior in accordance with the RSJ model.
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85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Fabrication of thin film Nb‐(fine Nb wires)‐NbN weak links for superconducting quantum interference device applications

H. Abe, K. Hamasaki, and Y. Ikeno

Appl. Phys. Lett. 61, 1131 (1992); http://dx.doi.org/10.1063/1.107691 (3 pages) | Cited 4 times

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Thin film Nb‐(fine Nb wires)‐NbN dc‐superconducting quantum interference devices (SQUIDs) with well‐balanced critical current have been reproducibly fabricated by applying an electric field simultaneously to two insulating Nb/MgO/NbN edge‐sandwiches (each junction area=0.2 μm2) in a superconducting loop, in liquid helium. Although the critical current of a dc‐SQUID is not yet controlled sufficiently, this fabrication technique is well suited to use in short weak link dc‐SQUIDs, thanks to the reproducibility of dc‐SQUIDs with well‐balanced critical current, the simplicity of fabrication processes, and the large device resistance.
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85.25.Cp Josephson devices
85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.50.+r Tunneling phenomena; Josephson effects

a‐axis oriented growth of YBa2Cu3O7−y films on LaSrGaO4(100) substrates

S. Hontsu, N. Mukai, J. Ishii, T. Kawai, and S. Kawai

Appl. Phys. Lett. 61, 1134 (1992); http://dx.doi.org/10.1063/1.107692 (3 pages) | Cited 30 times

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We have grown a‐axis oriented YBa2Cu3O7−y (YBCO) films on LaSrGaO4 (LSGO) (100) substrates with (100) oriented seed layer of PrBa2Cu3O7−x (PBCO) using a pulsed laser deposition technique. PBCO films on LSGO (100) deposited even at ∼800 °C exhibits the a‐axis orientation. In this temperature range, PBCO films on SrTiO3 (100) substrate exhibits the c‐axis orientation. The YBCO film with a‐axis orientation was grown on this PBCO(100) layer at a wide range of 650–800 °C. The YBCO films on PBCO free substrates have, on the other hand, c‐axis orientation normal to the surface of the LSGO (100). We found that the preferred orientations of YBCO thin films can be controlled by the presence of PBCO films on LSGO substrate. For the a‐axis orientated YBCO films, the resistance perpendicular to the c axis is 1/2 of that parallel to the c axis, suggesting the preferred orientation of c axis along the surface. The zero resistance superconducting transition temperature (Tc) of the films on the LSGO (100) and PBCO (100)/LSGO (100) substrates are 88.0 and 89.0 K, respectively.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Local poling of ferroelectric polymers by scanning force microscopy

P. Güthner and K. Dransfeld

Appl. Phys. Lett. 61, 1137 (1992); http://dx.doi.org/10.1063/1.107693 (3 pages) | Cited 125 times

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We have demonstrated a new technique to polarize locally micron‐sized areas of a ferroelectric vinylidene‐fluoride trifluoroethylene (VDF‐TrFE) copolymer film by locally applying a dc voltage between the tip of a scanning force microscope and the bottom electrode underneath the polymer film. To detect these polarized regions we have stimulated the film piezoelectrically by applying an ac electric field between tip and bottom electrode, and measuring locally amplitude and phase of the surface vibration. The size of the smallest region we could polarize so far was about 1 μm.
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77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
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