REGULAR ISSUE PAPERS
Role of Interfacial-Charge in the Growth of GaN on -SiC
SHANG YUAN REN1 and JOHN D. DOW2
1--Department of Physics, Peking University, Beijing 100871, People's Republic of China and Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504. 2--Department of Physics and Astronomy, Arizona State University, Tempe, AZ
85287-1504.
KEY WORDS
6H-SiC, GaN, substrate
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The growth of GaN and AlN films on (0001) substrates of 6H-SiC has
produced high-quality opto-electronic films. The SiC surface at the interface
with GaN or AlN is either Si-terminated or C-terminated, and the Si-terminated
interface is known to be the better substrate, producing higher-quality films.
The polarity of the interface is important, as recognized by Sasaki and
Matsuoka. We propose that the main relevant parameter for characterizing the
interface and its potential for producing high-quality opto-electronic GaN or
AlN films is the interfacial charge, which leads to the best films when the
charge is positive and relatively large. The positive charge reduces the size
of the N ions at the interface and hence improves the local lattice
match. (The charges are approximately -0.45 |e| and +0.55 |e| on the
interfacial N and Si atoms, respectively.) Therefore, while the polarity of the
interface is important, the polarity's effect on the local lattice mismatch is
what leads to a high-quality interface. These ideas are consistent with XPS
data and are supported by electronegativity arguments, by calculations for
ordinary mono-bonded GaN/SiC superlattices (with N-Si and Ga-C interfaces) and
by computations for superlattices with tri-bonded interfaces. We predict that
the tri-bonded N-Si interface of GaN/SiC should produce excellent GaN and AlN
films.
InAsSb/InTlSb Superlattice: A Proposed Heterostructure for Long Wavelength Infrared Detectors
S. IYER,1 J. LI,2 S. CHOWDHURY-NAGLE,2 and K.K. BAJAJ3
1--Department of Electrical Engineering, North Carolina A&T State
University, Greensboro, NC 27411. e-mail address: iyer@garfield.ncat.edu. 2--Department of Electrical Engineering, North Carolina A&T State University, Greensboro, NC 27411. 3--Department of Physics, Emory University, Atlanta, GA 30322.
KEY WORDS
InAsSb/InTlSb, long wavelength infrared (LWIR) detector,
superlattice
|
A novel superlattice (SL) heterostructure, comprising of InTlSb well and
InAsSb barrier lattice matched to InSb, is proposed for long wavelength 8-12 µm
detectors. Improvements in the InTlSb epilayers' structural quality are
expected, as it will be sandwiched between higher quality zinc-blende InAsSb
epilayers. Preliminary energy band calculations of 30Å
InAs0.07Sb0.93/100Å
In0.93Tl0.07Sb SL show the band alignment favorable to
type I with three heavy-hole subband confinement in the valence band and a
partial electron subband confinement in the conduction band due to the small
conduction band offset. Including the effect of strain indicates significant
changes in the band offsets, with optical bandgap essentially unaltered. The
optical band gap of this SL was computed to be 0.127 eV (9.7 µm) at 0K,
indicating its potential for long wavelength applications.
Deposition of Tantalum Oxide Films by Dual Spectral Source Assisted
Metalorganic Chemical Vapor Deposition (MOCVD)
Y. CHEN,1 R. SINGH,2 and J. NARAYAN3
1--Department of Electrical and Computer Engineering, Clemson University,
Clemson, SC 29634-0915. 2--Department of Electrical and Computer Engineering, Clemson University, Clemson, SC 29634-0915. e-mail address: raj.singh@ces.clemson.edu. 3--Materials Science and Engineering Department, North Carolina State University, Raleigh, NC 27695.
KEY WORDS
Dielectrics, metalorganic chemical vapor deposition (MOCVD),
rapid isothermal processing (RIP)
|
Dual spectral source assisted metalorganic chemical vapor deposition
(MOCVD) is an ideal technique for the deposition of high dielectric constant
materials. Tungsten halogen lamps and a deuterium lamp are used as the sources
of optical and thermal energy. In this paper, we have reported the deposition
and characterization of tantalum penta oxide films. Ta2O5
films were deposited at 660°C for 15 min and annealed at 400° for 1 h.
The leakage current densities of 10.6 nm thick films are as low as
10-10 A/cm2 for gate voltage under 4V. To the best of our
knowledge, these are the best results reported to date by any researcher. The
high energy photons used in the in-situ cleaning and deposition process
play an important role in obtaining high quality films of
Ta2O5.
Chemical Beam Epitaxial Growth of InP Using EDMIn and BPE
C.W. KIM, L.P. SADWICK, and G.B. STRINGFELLOW
College of Engineering, University of Utah, Salt Lake City, Utah 84112.
KEY WORDS
BPE, chemical beam epitaxy, EDMIn, InP
|
The effect of the growth temperature on the quality of InP grown by
chemical beam epitaxy (CBE) using ethyldimethylindium (EDMIn) and
bisphosphinoethane (BPE) are presented. The growth rate was nearly independent
of growth temperature, BPE flow rate, and cracker cell temperature in the range
from 700 to 900°C. Smooth and mirror-like surfaces were obtained for all of
the samples grown at temperatures above 465°C. All of the InP samples were
n-type. As the growth temperature increased, the net carrier concentration
decreased and reached a minimum value of 3.2 x 1015 cm-3
at 485°C. The electron mobility increased with increasing growth
temperature, reaching values of 3630 and 21800 cm2/Vs at 300 and
77K, respectively. The photoluminescence was found to depend strongly on the
growth temperature. Excitonic luminescence was detected only for growth
temperatures above 465°C. The intensity of the band edge emission is
comparable to that of the acceptor related emission for layers grown at
465°C. At 485°C, the band-edge recombination is dominant and the acceptor
related emission is barely observable. As the growth temperature increased from
465 to 485°C, the full width at half maximum of the bound exciton peak
decreased from 6.8 to 3.5 meV at 14K. This trend was consistent with the
decrease in the impurity concentration deduced from the Hall effect
measurements.
Effects of Trimethylindium on the Purity of
In0.5Al0.5P and In0.5Al0.5As
Epilayers Grown by Metalorganic Chemical Vapor Deposition
J.C. CHEN,1 Z.C. HUANG,1,2 and K.J. LEE1,3 and RAVI KANJOLIA4
1--Department of Computer Science and Electrical Engineering, University of Maryland Baltimore County, Baltimore, MD 21228. 2--Also with Hughes-STX Corporation, 7701 Greenbelt Road, Suite 400, Greenbelt, MD 20770. 3--Also with Department of Electrical Engineering, University of Maryland, College Park, College Park, MD 20742. 4--Morton International, Inc., Danvers, MA 01923.
KEY WORDS
InAlP, InAlAs, metalorganic chemical vapor deposition
(MOCVD), trimethylindium (TMIn)
|
In0.5Al0.5P lattice-matched to GaAs and
In0.5Al0.5As lattice-matched to InP epilayers were grown
by atmospheric pressure metalorganic chemical vapor deposition (AP-MOCVD). The
effect of trimethylindium on the purity of the as-grown layers was
systematically studied using secondary ion mass spectroscopy (SIMS), deep level
transient spectroscopy (DLTS), and capacitance-voltage (C-V) measurements. The
SIMS results showed that oxygen is the main impurity in all layers and the
oxygen concentration in InAlP was approximately one to four orders of magnitude
higher than the oxygen concentration found in InAlAs when the same indium
source was used, indicating that more oxygen was introduced by the phosphine
source than by the arsine source. Two electron traps in the InAlP epilayers and
four electron traps in the InAlAs epilayers were observed in this study. When a
high-purity indium source was used, the best InAlP epilayer showed only one
deep electron trap at 0.50 eV while the best InAlAs epilayer showed no deep
levels measured by DLTS. In addition, we also found that a high concentration
of oxygen is related to the high resistivity in both material systems; this
suggests that semi-insulating (SI) materials can be achieved by oxygen doping
and high quality conducting materials can only be obtained through the
reduction of oxygen. The oxygen concentration measured by SIMS in the best
InAlAs epilayer was as low as 3 x 1017 cm-3.
Characterization of Organic Thin Films for OLEDs Using Spectroscopic Ellipsometry
FRANCIS G. CELII, TRACY B. HARTON, and O. FAYE PHILLIPS
Semiconductor Research & Development/Technology, Texas Instruments, Inc., M/S 147, P.O. Box 655936, Dallas, TX 75265.
KEY WORDS
Organic films, organic light emitting diodes (OLEDs),
spectroscopic ellipsometry
|
We report the optical characterization of thin, evaporated organic films
used in fabrication of organic light emitting diodes (OLEDs):
N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-1,1'biphenyl-4,4'diamine, or TPD, and
tris (8-hydroxy) quinolato aluminum, or Alq3. In particular, we have
obtained and analyzed spectroscopic ellipsometry (SE) data using a multi-sample
approach, to determine the optical constants for Alq3 and TPD films
over the wavelength range 250-850 nm. We show that bi-layer Alq3/TPD
films on Si can be analyzed for individual layer thicknesses, even though the
refractive index is nearly identical for these films in the visible region.
Simulations of in situ monitoring are also presented, which show sub-nm
thickness resolution for organic layer growth on a Si monitor wafer. SE has
great utility for process control, either by ex situ or in situ
thickness measurement.
Defect State Assisted Tunneling in Intermediate Temperature Molecular Beam Epitaxy Grown GaAs
A.E. YOUTZ,1 B. NABET,2 and F. CASTRO2
1--Electrical and Computer Engineering Department, Drexel University,
Philadelphia, PA 19104. Present address: Lucent Technologies, 330 S. Randolphville Rd., Piscataway, NJ 08854. 2--Electrical and Computer Engineering Department, Drexel University, Philadelphia, PA 19104.
KEY WORDS
Defect assisted tunneling, low-temperature-grown GaAs,
metal-semiconductor-metal (MSM) detectors, Schottky contacts, thermal
annealing
|
Current transport in molecular beam epitaxy (MBE) GaAs grown at low and
intermediate growth temperatures is strongly affected by defects. A model is
developed here that shows that tunneling assisted by defect states can
dominate, at some bias ranges, current transport in Schottky contacts to
unannealed GaAs material grown at the intermediate temperature range of about
400°C. The deep defect states are modeled by quantum wells which trap
electrons emitted from the cathode before re-emission to semiconductor.
Comparison of theory with experimental data shows defect states of energies
about 0.5 eV below conduction band to provide the best fit to data. This
suggests that arsenic interstitials are likely to mediate this conduction.
Comparison is also made between as-grown material and GaAs grown at the same
temperature but annealed at 600°C. It is suggested that reduction of these
defects by thermal annealing can explain lower current conduction at high
biases in the annealed device as well as higher current conduction at low
biases due to higher lifetime. Quenching of current by light in the as-grown
material can also be explained based on occupancy of trap states.
Identification of this mechanism can lead to its utilization in making ohmic
contacts, or its elimination by growing tunneling barrier layers.
Effects of Aluminum Sputtering Process Parameters on
Via Step Coverage in Micro-Electronic Device Manufacturing
G. DePINTO,1 S. DUNNIGAN,1 K. SCHWECHEL1 and B. MISHRA2
1--MOS 8 Process Engineering, Motorola, 3501 Ed Bluestein Blvd., Austin, TX
78721. 2--Department of Metallurgical & Materials Engineering, Colorado School of
Mines, Golden, CO 80401.
KEY WORDS
Argon pressure, chamber configuration, PVD aluminum,
step coverage, temperature
|
It has been observed that the step coverage achieved for aluminum
deposition at 200°C on a multi-chamber (ultra-high vacuum) horizontal
physical vapor deposition (PVD) system (System A) is electrically comparable to
the step coverage on a single chamber, high vacuum (vertical) PVD system
(System B) at 300°C under the optimized conditions of pre-clean process,
sputtering power, argon pressure and chamber hardware configuration. In
addition, it has been determined that the metal step coverage is relatively
poor at temperatures higher than 200°C on System A, whereas the metal step
coverage on System B is better at 300°C when compared with both
substantially lower and higher temperatures. Since step coverage is a vital
parameter in the manufacturing of sub-micron devices with high aspect ratio
vias, the effect of the sputtering process parameters has been studied. This
work investigates possible causes for the observed temperature effect and
evaluates possible methods for improving the step coverage. The directionality
of sputtering and film-substrate bonding are identified as two primary factors
controlling step coverage.
Scanning Tunneling Potentiometry Study of Electron Reflectivity of a Single Grain Boundary in Thin Gold Films
M.A. SCHNEIDER, M. WENDEROTH, A.J. HEINRICH, M.A. ROSENTRETER, and R.G. ULBRICH
Universität Göttingen, IV. Physikalisches Institut, Bunsenstr. 13,
D-37073 Göttingen, Germany.
KEY WORDS
Grain boundary scattering, scanning tunneling microscopy
(STM), scanning tunneling potentiometry (STP), thin film resistivity
|
Spatial variations of the local electric field in current-carrying thin
gold films were studied with a scanning tunneling microscope on a nanometer
scale. With a refined scanning tunneling potentiometry technique, it was
possible to determine the local electric fields within single grains. At grain
boundaries, we observe potential drops on length scales of less than 1 nm which
exceed the potential difference within a grain greatly. We interpret our
findings by applying a theory that models grain boundaries as barriers with a
reflectivity R for the conduction electrons. With the assumption of
isotropic background scattering within each grain, we determine the local
current-density j(x,y) that passes a grain boundary. From that, we obtain the
reflectivity of individual grain boundaries and find values of R = 0.7 to R =
0.9 which is much higher than expected from macroscopic experiments.
Influence of AlN Protective Film Thickness on the Hardness and
Electrophotographic Properties of Organic Photoconductors
X.S. MIAO,1 Y.C. CHAN,1 C.K.H. WONG,1 D.P. WEBB,1 Y.W. LAM,1 K.M. LEUNG,2 and D.S. CHIU2
1--Department of Electronic Engineering, City University of Hong Kong, Hong
Kong. 2--Department of Physics and Materials Science, City University of
Hong Kong, Hong Kong.
KEY WORDS
AlN film, electrophotographic properties, microhardness,
organic photoconductor
|
The deposition of a protective film to increase the hardness of an
organic photoconductor (OPC) surface is an effective method to lengthen the
lifetime of the OPC. In this work, AlN protective films were deposited onto OPC
samples by rf reactive magnetron sputtering with low substrate temperature. The
AlN films were deposited with optimized sputtering conditions and exhibited
very high transmissivity in the visible wavelength range 300~800 nm. The films
caused a remarkable increase in the hardness of the OPC surface, by between 32
and 62%. The acceptance voltage, dark decay rate, photodischarge rate,
difference between the residual potential and the acceptance voltage of the OPC
protected by AlN film were improved. These results show AlN is a suitable
protective film for OPC.
A Comparison of the Critical Thickness for MBE Grown LT-GaAs Determined by
In-Situ Ellipsometry and Transmission Electron Microscopy
K.G. EYINK,1 M.A. CAPANO,1 S.D. WALCK,1 T.W. HAAS1 and B.G. STREETMAN2
1--Materials Directorate, 2941 P St. Ste. 1, Wright-Patterson AFB, OH
45433-6533. 2--The University of Texas, Microelectronics Research Center, MER 1.606/R9900
Austin TX 78712.
KEY WORDS
Defects, ellipsometry, low temperature (LT) GaAs, molecular
beam epitaxy (MBE)
|
The growth of low temperature (LT) GaAs by molecular beam epitaxy has
been studied using ellipsometry. Different regimes of growth were observed in
the data, depending on film thickness. Epitaxial growth of pseudomorphic
LT-GaAs occurred immediately above the substrate, followed by a layer with
changing dielectric properties. This upper layer can be modeled as a two-phase
region consisting of epitaxial LT-GaAs and small grained, polycrystalline GaAs,
which increases in volume fraction with increasing layer thickness. For
sufficiently thick LT layers cross-sectional transmission electron microscopy
analysis showed pyramidal defects that were composed primarily of highly
twinned regions. The ellipsometry data showed a deviation from the homogeneous
growth model at a thickness less than the thickness at which the pyramidal
defects nucleated in all samples.
Study of Amorphous Ta2O5 Thin Films by DC Magnetron
Reactive Sputtering
K. CHEN,1 M. NIELSEN,1 G.R. YANG,1 E.J.
RYMASZEWSKI,2 and T.-M. LU1
1--Center for Integrated Electronics and Electronic Manufacturing, Rensselaer Polytechnic Institute, Troy, New York, 12180. Also with Physics Department. 2--Center for Integrated Electronics and Electronic Manufacturing, Rensselaer Polytechnic Institute, Troy, New York, 12180. Also with Material Engineering Department.
KEY WORDS
dc magnetron reactive sputtering, stoichiometry, tantalum
oxide thin films, x-ray photoelectron spectroscopy
|
The dc magnetron reactive sputtering deposition of tantalum pentoxide
(Ta2O5) thin films was investigated. By combining
Schiller's criterion and Reith's "target preoxidation" procedure, high quality
Ta2O5 thin films were prepared at a high deposition rate
of about 100Å/min. The deposited films were amorphous, with a refractive
index around 2.07 and a dielectric constant of 20. An optical transmittance of
98.6% was obtained for a 4500Å thick film. The leakage current density is
5 x 10-9 A/cm2 at an electric field strength of 1 MV/cm
and its breakdown field strength is above 2 MV/cm. The temperature coefficient
of capacitance for capacitors fabricated using the deposited films is
approximately +230 ppm/°C. X-ray photoelectron spectroscopy shows that the
films are stoichiometric tantalum pentoxide, Ta2O5, and
exhibit good stability.
Chemical Vapor Deposition and Characterization of Amorphous Teflon Fluoropolymer Thin Films
R. SHARANGPANI,1 R. SINGH,2 M. DREWS,3 and K. IVEY4
1--Department of Electrical and Computer Engineering, Clemson University,
Clemson, SC 29634-0915. 2--Department of Electrical and Computer Engineering and Materials Science and Engineering Program, Clemson University, Clemson, SC 29634-0915. e-mail address:raj.singh@ces.clemson.edu. 3-School of Textiles and Materials Science and Engineering Program, Clemson University, Clemson, SC 29634-1307. 4--School of Textiles, Clemson University, Clemson, SC 29634-1307.
KEY WORDS
Direct liquid injection, low dielectric constant (K)
interconnect dielectrics, rapid isothermal processing (RIP), ultra violet (UV)
light assisted processing
|
Dielectric materials with dielectric constant (K) less than the
conventionally used SiO2 (K = 3.9) are gaining importance
particularly for low voltage operated integrated circuits due to their ability
to reduce signal propagation delays, power dissipation, and crosstalk when used
as interconnect dielectrics. In this paper, we report for the first time ever a
chemical vapor deposition technique for the deposition of the copolymeric
amorphous Teflon fluoropolymer AF 1600 which is a new low K material with a
value of K of about 1.93. The principle of direct liquid injection in an
ultra-violet (UV) light assisted rapid isothermal processing system was
followed. Different processing cycles were studied with and without the UV
source to investigate the effect of high energy photons during processing on
the film properties. Preliminary characterization results indicate that the
processed films exceed the established dielectric performance standards
required for future generation IC manufacturing. An improvement in film
properties was observed when the UV source was used during processing.
InxGa1-xAs Ohmic Contacts to n-Type GaAs with a Tungsten Nitride Barrier
CHIHIRO J. UCHIBORI,1 Y. OHTANI,1 T. OKU,1 NAOKI ONO,2 and MASANORI MURAKAMI3
1--Division of Materials Science and Engineering, Department of Engineering
Science, Kyoto University, Sakyo-ku, Kyoto 606, Japan. 2--Mitsui Mining & Smelting Co. LTD., 2081 Karafune, Oaza, Omuta, Fukuoka 836, Japan. 3--Division of Materials Science and Engineering, Department of Engineering Science, Kyoto University, Sakyo-ku, Kyoto 606, Japan.
KEY WORDS
Diffusion barrier, InxGa1-xAs, n-type
GaAs, ohmic contact, radio frequency sputtering, tungsten nitride
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Significant reduction of the contact resistance of In0.7Ga0.3As/Ni/W contacts (which were previously developed by sputtering in our laboratory) was achieved by depositing a W2N barrier layer between the Ni layer and W layer. The
In0.7Ga0.3As/Ni/W2N/W contact prepared by the
radio-frequency sputtering technique showed the lowest contact resistance of
0.2 mm after annealing at 550°C for 10 s. This contact also provided
a smooth surface, good reproducibility, and excellent thermal stability at
400°C. The polycrystalline W2N layer was found to suppress the In
diffusion to the contact surface, leading to improvement of the surface
morphology and an increase in the total area of the
InxGa1-xAs between metal and the GaAs substrate. These
improvements are believed to reduce the contact resistance.
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