Permanent-Magnet Materials: Research Directions and Opportunities
R.H. RICHMAN1and W.P. McNAUGHTON2
1--Daedalus Associates, Inc., 2134 Old Middlefield Way, Mountain View, CA 94043. 2--Cornice Engineering, Inc., P.O. Box 2542, Durango, CO 81302.
Permanent magnets are pervasive in modern industrial societies. They enable conversion of electrical energy to mechanical energy, they underlie microwave communications, and they constitute the active material in data-storage devices. To sustain the evolution of new and improved permanent-magnet materials, an active research enterprise is required. In this paper, the status of modern rare earth-transition metal magnets is outlined, contemporary research directions are summarized, and unresolved issues and research opportunities are enumerated.
Permanent-magnetic materials, rare earth-transition metals
REGULAR ISSUE PAPERS
Surface Treatment of ZnSe Substrate and Homoepitaxy of ZnSe
M.W. CHO,1 K.W. KOH,1 K. MORIKAWA,1 K. ARAI,1 H.D. JUNG,1 Z. ZHU,1 T. YAO2 and Y. OKADA3
1--Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980, Japan. 2--Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980, Japan and Joint Research Center for Atom Technology, National Institute for Advanced Interdisciplinary Research, Tsukuba 305, Japan. 3--Electrotechnical Laboratory, Umezono, Tsukuba 305, Japan.
High quality ZnSe(100) substrates have been used for homoepitaxial growth by molecular beam epitaxy. A chemical pretreatment suitable for ZnSe substrate preparation is determined from x-ray photoemission spectroscopy studies. Thermal cleaning processes for the ZnSe(100) surface were investigated by in-situ reflection high energy electron diffraction and the surface phase diagram for ZnSe(100) was obtained for the first time. The low temperature photoluminescence spectra recorded from homoepitaxial layers exhibit unsplit free and bound exciton transitions with strong intensities. The full widths at half maximum of the (400) x-ray diffraction spectra for ZnSe homoepitaxial layer were 17~31 arcsec.
Molecular beam epitaxy (MBE), surface treatment, ZnSe homoepitaxy
Dry Etching of III-V Semiconductors in IBr/Ar Electron Cyclotron Resonance Plasmas
J.W. LEE,1 J. HONG,1 E.S. LAMBERS,1 C.R. ABERNATHY,1 S.J. PEARTON,1 W.S. HOBSON,2 and F. REN2
1--Department of Materials Science & Engineering, University of Florida, Gainesville FL 32611. 2--Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974.
IBr/Ar plasmas were found to be promising candidates for room temperature dry etch processing of the III-V semiconductors GaAs, AlGaAs, GaSb, InP, InGaAs, and InSb. Results showed fast etch rates (~3,000Å/min) at high microwave power (1000W) and good surface morphology (typical root mean square roughness ~2 nm), while retaining the near-surface stoichiometry. There was little variation of surface smoothness over a wide range of plasma compositions for Ga-containing materials. By contrast, there was a plasma composition window of about 25-50% of IBr in IBr/Ar plasmas for maintaining good morphology of In-containing semiconductors like InP. Etch rates of the semiconductors generally increased with microwave power (400-1000 W) and rf power (50-250 W), whereas there was little dependence of the rates on the increasing percentage of IBr in the IBr/Ar plasma composition above 30% IBr for In-based, and 50% IBr for Ga-based materials. Those results show the etch rates over 30% of IBr in IBr/Ar are desorption-limited. Photoresist masks do not hold up well to the IBr under ECR conditions, resulting in poor profile control, whereas SiNx offers much better etch resistance.
III-V semidconductors, electron cyclotron resonance, etching, plasmas, reactive ion etching
Laser-Induced Direct Etching of GaAs Using Chlorofluorocarbon (CFC) Alternative Gases
MOO-SUNG KIM,1 CHEON LEE,2 SE KI PARK,2 WON CHEL CHOI,1 EUN KYU KIM,3 SEONG-IL KIM,1 BYOUNG SUNG AHN,1 and SUK-KI MIN1
1--Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Korea. 2--Department of Electrical Engineering, Inha University, Inchon 402-751, Korea. 3--Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Korea. e-mail: firstname.lastname@example.org.
Non-ozone layer destructive chlorofluorocarbon (CFC) alternatives have been initially used for laser-induced thermochemical etching of GaAs. The CFC alternatives used here are CHClF2 and C2H2F4. Respective etching rates of 188 and 160 µm/s were achieved using CHClF2 and C2H2F4 gases. Aspect ratios of 2.5 and 1.5 were achieved with a single laser scan for CHClF2 and C2H2F4, respectively. The presence of some reaction products deposited on the etched region was dependent on three variables: laser power, scan speed, and gas pressure. Chemical compositions of the reaction products were measured by Auger electron spectroscopy.
Ar ion laser, chlorofluorocarbon (CFC) alternative, GaAs,
high aspect ratio, high speed etching, laser-induced etching, maskless
Nearly Room-Temperature Type-II Quantum-Well Lasers at 3-4 µm
CHIH-HSIANG LIN,1 P.C. CHANG,1 S.J. MURRY,1 D. ZHANG,1 RUI Q. YANG,1 S.S. PEI1 J.I. MALIN,2 J.R. MEYER,2 C.L. FELIX,2 J.R. LINDLE,2 L. GOLDBERG,2 C.A. HOFFMAN,2 and E.J. BARTOLI2
1--Space Vacuum Epitaxy Center, University of Houston, Houston, TX 77204-5507. 2--Code 5600, Naval Research Laboratory, Washington, DC 20375.
We report optically pumped four-constituent InAs/lnGaSb/InAs/AlSb type-II
quantum-well lasers emitting at 3.2-4.1 µm. Lasing was observed up to 350K
under pulsed operation, with a characteristic temperature T0 up to
68K at temperatures above ambient.
Laser diodes, mid-infrared, type-II heterostructures, quantum wells
LPE Growth of Crack-Free PbSe Layers on Si(100) Using MBE-Grown PbSe/BaF2/CaF2 Buffer Layers
B.N. STRECKER,1 P.J. McCANN,1 X.M. FANG,1 R.J. HAUENSTEIN,2 M. O'STEEN,2 and M.B. JOHNSON3
1--School of Electrical and Computer Engineering and Laboratory for Electronic Properties of Materials, University of Oklahoma, Norman, OK 73019. 2--Department of Physics, Oklahoma State University, Stillwater, OK 74078. 3--Department of Physics and Astronomy and Laboratory for Electronic Properties of Materials, University of Oklahoma, Norman, OK 73019.
Crack-free PbSe on (100)-oriented Si has been obtained by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. MBE is employed first to grow a PbSe/BaF2/CaF2 buffer structure on the (100)-oriented Si. A 2.5 µm thick PbSe layer is then grown by LPE. The LPE-grown PbSe displays excellent surface morphology and is continuous over the entire 8 x 8 mm2 area of growth. This result is surprising because of the large mismatch in thermal expansion coefficients between PbSe and Si. Previous attempts to grow crack-free PbSe by MBE alone using similar buffer structures on (100)-oriented Si have been unsuccessful. It is speculated that the large concentration of Se vacancies in the LPE-grown PbSe layer may allow dislocation climb along higher order slip planes, providing strain relaxation.
IV-VI semiconductors, BaF2, CaF2,
Structural, Electrical, and Optical Studies of GaAs Implanted with MeV As or Ga Ions
J. JASINSKI,1 Z. LILIENTAL-WEBER,2 J. WASHBURN2 H.H. TAN,3 C. JAGADISH,3 A. KROTKUS,4 S. MARCINKEVICIUS,5 and M. KAMINSKA6
1--Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720. On leave from Institute of Experimental Physics, Warsaw University, Poland. 2--Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720. 3--Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, ACT 0200 Canberra, Australia. 5--Semiconductor Physics Institute, A. Gostauto 11, 2600 Vilnius, Lithuania. 6--Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw, Poland. Also at Department of Physics II, Royal Institute of Technology, Stockholm, Sweden.
The structural properties of GaAs implanted with high doses of 2 MeV arsenic or
gallium ions with subsequent annealing at different temperatures were studied
by transmission electron microscopy, Rutherford backscattering
spectrometry-channeling, double crystal x-ray diffraction. Optical absorption,
electrical conductivity, Hall effect and time-resolved photoluminescence were
applied to monitor changes in electrical and optical characteristics of the
material. An important conclusion from this investigation is that there was
hardly any difference between materials implanted with gallium or arsenic. For
implantation of either species, a large number of point defects was introduced
and for a high enough dose a buried amorphous layer was formed. Hopping
conduction and high absorption below band-to-band transition were observed for
both cases. After low temperature annealing of the amorphous material, a high
density of stacking faults and microtwins were found. Regrowth rates at the
front and back amorphous-crystalline interfaces showed a significant
difference. This was attributed to differences in local nonstoichiometry of the
material at the upper and lower amorphous-crystalline interfaces. Structural
studies showed the presence of some residual damage (a band of polycrystalline
material in the center of the regrown area) with some associated strain even
after annealing at high temperatures. Recovery to the conduction band transport
in annealed samples was observed but mobilities, of the order of 2000
cm2/Vs, were still smaller than in unimplanted GaAs. These results
show that, in as-implanted material and even after annealing at lower
temperatures, the point defects introduced by the implantation are responsible
for the very short photocarrier lifetime.
GaAs, ion implantation, point defects
Chemical Composition and Thermal Stability of 2 Butyl, 5 Chloro, Benzimidazole Film
V. SIRTORI, L. LOMBARDI, and G. REDAELLI
IBM Semea, Department 424, Via Lecco 61, 20059 Vimercate, Italy.
The stability of a 2 butyl, 5 chloro, benzimidazole film (BCB) before and after
a thermal treatment, which simulated the annealing of a typical soldering
process, was the main motivation of the present work. The chemical bonds inside
the BCB film and between this film and the copper substrate were investigated
by x-ray photoelectron spectroscopy (XPS). The thickness of that film was
measured by optical ellipsometry. Protection of the film vs oxidation and its
physical modification during the thermal treatment were also invest igated. The
XPS valence data showed that a part of the chlorine was linked to the benzene
ring while the other part formed either copper chloride or another chloride
linked to the nitrogen of the BCB molecule. The passivation film hardened and
became an electric insulator during the thermal treatment, so that any
successive electrical test was impaired.
Benzimidazole, copper surface, inhibitor, x-ray photoelectron spectroscopy (XPS)
Defect Characterization of n-Type Si1-xGex After 1.0 keV Helium-Ion Etching
S.A. GOODMAN,1 F.D. AURET,1 K. NAUKA,2 and J.B. MALHERBE1
1--Physics Department, University of Pretoria, Pretoria, 0002, South Africa. 2--Hewlett Packard Co., Palo Alto, CA 94304.
SiGe heterostructures with their associated geometries and properties promise a
novel generation of Si-based devices. Surface processing and, in particular,
dry or plasma etching of semiconductors is a key technology for producing
optoelectronic integrated circuits and high speed electronic devices. We have
used deep-level transient spectroscopy (DLTS) in an investigation of the
electronic properties of defects introduced in n-Si1-xGex
(x = 0.00 to 0.25) during 1 keV helium-ion etching (fluence = 1 x
1012 cm-2) prior to the deposition of gold Schottky
barrier diodes (SBDs). Six electron defects (EHe1-EHe6) were detected after
this processing stage. The defects detected after etching are compared to those
introduced by 5.4 MeV alpha-particle (-) irradiation and, also, radio frequency (rf) sputter-deposition of Au SBDs on material from the same wafer.
Four of the electron defects (EHe1, EHe2, EHe4, and EHe6) are detected in Si.
The remaining two defects (EHe3 and EHe5) are only detected in material
containing germanium. It was noted that defects introduced during the He-ion
etch process have the same DLTS "signatures" as defects after the sputter
deposition process, but none were the same as those introduced during the
-particle irradiation. The influence of increased Ge content on DLTS peak shape and positions is also illustrated and discussed.
Deep level transient spectroscopy (DLTS), defects, helium-ion
etching, SiGe, sputter-deposition
Thermally Stimulated Current Measurements on a UV Irradiated Organic Photoreceptor Layer
D.P. WEBB,1 Y.C. CHAN,1 C.K.H. WONG,1 Y.W. LAM,1 K.M. LEUNG,2 and D.S. CHIU2
1--Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong. 2--Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
Thermally stimulated current (TSC) measurements have been performed on a xerographic photoreceptor which has been treated with ultraviolet (UV) radiation. The charge transport layer of the photoreceptor consists of a polyester molecularly doped with an arylamine substituted hydrazone which was observed to undergo UV induced rearrangement to an indazole derivative. The indazole derivative is transparent to the wavelength component inducing the photo-reaction so that the depth of converted material gradually extends farther into the CTL with UV exposure time. The xerographic residual potential variation with irradiation time is attributed to the formation of a potential barrier to transfer of charge from hydrazone hopping states to indazole hopping states. The mobility activation energy obtained from TSC measurements is 0.22 eV for unirradiated material, which decreases to 0.12 eV after 1200 s of irradiation. The latter energy is identified as a signature of the potential barrier. This identification is corroborated by the correlation between the decrease of the residual potential and the increase of the TSC activation energy after 3600 s of irradiation.
Thermally stimulated current, UV radiation, xerographic photoreceptor
Improved Reproducibility of AlGaInAs Laser Threshold by InP Substrate Deoxidation under Phosphorous Flux
J.C. HARMAND, E. IDIART-ALHOR, J.M. MOISON, and F. BARTHE
France Telecom/CNET Laboratoire de Bagneux, 196 avenue Henri Ravera, BP 107, 99225 Bagneux Cedex, France.
When AlGalnAs laser structures are grown by molecular beam epitaxy on InP, the substrate deoxidation procedure is found to influence the quality of the structure: the laser threshold current densities are found to be low and reproducible when P2 is used for the substrate deoxidation. On the other hand, the reproducibility is not achieved with a deoxidation under As2. In order to interpret this result, very thin AlInAs overlayers have been deposited on InP substrates which were preliminarily deoxidized under P2 or As2 flux. The AlInAs morphology is observed by atomic force microscopy. The InP anneal under As2 leads to a rough surface as compared to the InP anneal under P2. These observations suggest that a systematic use of P2 for the substrate deoxidation can definitely improve the reliability of AlGaInAs laser structures on InP.
AlGaInAs lasers, atomic force microscopy, molecular beam epitaxy, surface deoxidation
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