JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 26, Number 2, February 1997 This Month Featuring: Regular Issue Papers and Letters. View February 1997 Table of Contents.

REGULAR ISSUE PAPERS

KEY WORDS Defect generation, flux ratio, interface chemistry, stacking faults, surface stoichiometry, ZnSe/GaAs

The existence of Zn-As and vacancy-contained Ga-Se interfacial layers are suggested by transmission electron microscopy of Zn- and Se-exposed (or -reacted) ZnSe/GaAs interfaces, respectively. A very low density of faulted defects in the range of ~10⁴/cm² was obtained in samples with Zn passivation on an As-stabilized GaAs-(2 x 4). However, the density of As precipitates increases as the surface coverage of c(4 x 4) reconstruction increased on the Zn-exposed As-stabilized GaAs-(2 x 4) surface and this is associated with an increase of the density of extrinsic-type stacking faults bound by partial edge dislocations with a core structure terminated on additional cations. On the other hand, densities of extrinsic Shockley- and intrinsic Frank-type stacking faults are of ~5 x 10⁷/cm² in samples grown on Se-exposed Ga-rich GaAs-(4 x 6) surfaces. Annealing on this Se-exposed Ga-rich GaAs-(4 x 6) generated a high density of vacancy loops (1 x 10⁹/cm²) and an increase of the densities of both Shockley- and Frank-type stacking faults (5 x 10⁸/cm²) after the growth of the films. Furthermore, we have studied the dependence of the generation and structure of Shockley-type stacking faults on the beam flux ratios in samples grown on Zn-exposed As-stabilized GaAs-(2 x 4) surfaces. Cation- and anion-terminated extrinsic-type partial edge dislocations were generated in samples grown under Zn- and Se-rich conditions, respectively. However, an asymmetric distribution on defect density under varied beam flux ratios (0.3 ¾ P_Se/P_Zn ¾ 10) is obtained.

Interface Structure in Arsenide/Phosphide Heterostructures Grown by Gas-Source MBE and Low-Pressure MOVPE
A.Y. LEW, C.H. YAN, R.B. WELSTAND, J.T. ZHU, C.W. TU, P.K.L. YU, and E.T. YU
University of California at San Diego, Department of Electrical and Computer Engineering, La Jolla, CA 92093-0407.

KEY WORDS GaAs, gas source molecular beam epitaxy (GSMBE), InGaAs/InP, low-pressure metalorganic vapor phase epitaxy (MOVPE)

We have used cross-sectional scanning tunneling microscopy (STM) to study interface structure in arsenide/phosphide heterostructures grown by gas-source molecular beam epitaxy (GSMBE) and by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). High-resolution images of GSMBE samples consisting of GaAs interrupted at 200Å intervals with a 40 s P₂ flux reveal substantial, growth-temperature-dependent incorporation of phosphorus with nanometer-scale lateral variations in interface structure. STM images of InGaAs/InP multiple quantum well structures grown by LP-MOVPE show evidence of interface asymmetry and extensive atomic cross-incorporation at the interfaces. Data obtained by STM have been corroborated by high-resolution x-ray diffraction and reflection high-energy electron diffraction. Together, these studies provide direct information about nanometer-scale grading and lateral nonuniformity of arsenide/phosphide interfaces that can occur under these growth conditions.

An Empirical Relation Between the Melting Point and the Direct Bandgap of Semiconducting Compounds
B.R. NAG
Calcutta University, 92 Acharya Prafulla Chandra Road, Calcutta-700009, India.

KEY WORDS Bandgap, entropy of fusion, melting point, semiconductor

The melting point is found to vary linearly with the direct bandgap for groups of semiconductors with common anions. Implication of this empirical result is discussed. The linear relation is used to choose between different reported values of metling point for some compounds.

Magnetic and Photomagnetic Properties of Polycrystalline Wide-Gap Semiconductor Cd_1-xMn_xTe Thin Films
X.-F. HE,¹ A. KOTLICKI,² P. DOSANJH,² B.G. TURRELL,² J.F. CAROLAN,² S. JIMENEZ-SANDOVAL,³ and P. LOZANO-TOVAR³
1--Department of Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada. Present Address: Department of Physics and Center for Electronic and Electro-Optic Materials, State University of New York at Buffalo, Buffalo, New York 14260. 2--Department of Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada. 3--Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del IPN Apartado Postal 14-740, 07000 Mexico D.F., Mexico.

KEY WORDS CdMnTe thin films, fiber-optic superconducting quantum interference device (SQUID) magnetometry, magnetization, polycrystalline, photomagnetization

The magnetic and photomagnetic properties of polycrystalline Cd_1-xMn_xTe thin films prepared by radio frequency (rf) sputtering have been investigated. Magnetization measurements were carried out using a rf superconducting quantum interference device magnetometer in the temperature range of 1.8~300K at various magnetic fields up to 5.5 T. For temperatures above 40K, Curie-Weiss behavior was observed with a negative Weiss constant indicating predominantly antiferromagnetic interactions. Spin-glass transitions occurred at low temperatures. Photoinduced magnetization has been observed when the sample was illuminated by unpolarized light from an optical fiber.

Study of Metal-Polymer Adhesion--A New Technology: Cu Plasma PIB
G.-R. YANG,¹ H. SHEN,² C. LI,³ and T.-M. LU¹
1--Department of Physics, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. 2--Department of Physics, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. Currently in the Department of Electrical and Computer Systems Engineering, Rensselaer Polytechnic Institute. 3--Material Science Department, Fudan University, Shanghai, China.

KEY WORDS Adhesion, Cu, plasma partially ionized beam (Plasma PIB), parylene-N (PA-N), secondary ion mass spectrosmetry (SIMS), x-ray photoelectron spectroscopy (XPS), plasma immersion ion implantation (PIII)

Adhesion between copper and n-type parylene (PA-N) has been studied. The PA-N film was deposited on Si (100) substrate by vapor deposition polymerization (VDP), and the Cu film was deposited on PA-N by plasma partially ionized beam (Plasma PIB) as well as other deposition techniques as a comparison. The adhesion strength was measured by 90deg. peel test after the sample was cleaved into a strip to define geometry. A peel strength of greater than 70 g/mm between the Cu film and PA-N was achieved by Cu Plasma PIB. X-ray photoelectron spectroscopy (XPS) studies found no Cu-O-C bond formation at Cu-parylene surface, while secondary ion mass spectrometry (SIMS) studies showed that a significant amount of Cu was shallowly implanted into the PA-N, with an average concentration of 10¹⁷-10¹⁸ atoms/cm³ near the interface. The results showed that a physically intermixing layer of about 100Å between the two phases formed by shallow implantation of Cu into PA-N was the main mechanism of adhesion. A suggested model is proposed correspondingly.

Interfacial Reaction and Electrical Property of Ge/Ni/ZnSe for Blue Laser Diode
DAE-WOO KIM,¹ JOON SEOP KWAK,¹ HEE-SOO PARK,¹ HWA NYUN KIM,¹ HONG KOO BAIK,¹ SUNG-MAN LEE,² CHANG-SOO KIM,³ and SAM-KYU NOH³
1--Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Korea. 2--Department of Materials Engineering, Kangwoen University, Chunchen Kangwoen-Do 200-701, Korea. 3--KRISS, Materials Evaluation Center, Daejon 305-606, Korea.

KEY WORDS Ge/Ni/ZnSe, Ni3Se2, Ni/ZnSe, Schottky barrier height, ZnSe

Interfacial reaction and electrical property of the Ge/Ni/ZnSe have been investigated as a fundamental study to develop ohmic contacts to p-ZnSe, using x-ray diffraction, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and capacitance-voltage measurement. Ni/ZnSe, Ni/Ge systems have been also studied for comparison with the Ge/Ni/p-ZnSe system and the electrical property could be related to the interfacial reaction. After annealing at 170°C, Ni₃Se₂ and NiGe were formed at Ni/ZnSe and Ge/Ni interface, respectively. The increase of annealing temperature resulted in the decomposition of Ni₃Se₂ through the reaction with Ge. The change of the Schottky barrier height strongly depended on the annealing temperature. According to the result of Ni/ZnSe interface reaction, Ni₃Se₂ in the Ni/ZnSe interface lowered the Schottky barrier height. At higher annealing temperature, the Schottky barrier height increased and it was mainly due to the thermal decomposition of ZnSe.

The Optimization of the Double Mask System to Minimize the Contact Resistance of a Ti/Pt/Au Contact
G.L. WAYTENA,¹ H.A. HOFF,¹ I.P. ISAACSON,² M.L. REBBERT,² D.I. MA,^2,3 CHRISTIE MARRIAN,² and J.S. SUEHLE⁴
1--Naval Research Laboratory, Washington, DC 20375. 2--Nanoelectronics Processing Facility, Naval Research Laboratory, Washington, DC 20375. 3--Author to whom inquires should be directed. 4--National Institutes of Standards and Technology (NIST), Gaithersburg, MD 20899.

KEY WORDS Contact resistance, diamond, metallization, ohmic contact, Ti diffusion, transmission line model

The fabrication of Ti/Pt/Au ohmic contacts on diamond using two transmission line model masks during the photolithography step was modified as a result of the adverse effects on the resistance from the rectifying lip created by the overlap of the two masks, and the possible inhibition of carbide formation due to the presence of oxygen on the diamond surface before metallization. The first modification consisted of decreasing the rectifying lip by diffusing a small amount of Ti from beneath the contact defined by the first mask, and decreasing the overlap of the two masks from 5 to 2 µm, which is close to the minimum allowable by our photolithography techniques. The second modification consisted of the desorption of oxygen from the diamond surface using a heat treatment in vacuum and cool down in purified hydrogen. As a result of these changes, the contact resistance was decreased by more than two orders of magnitude from 8.1 x 10^-2 -cm² to 1.2 x 10^-4 -cm².

Substitutional-Interstitial Silver Diffusion and Drift in Bulk (Cadmium,Mercury) Telluride: Results and Mechanistic Implications
IGOR LYUBOMIRSKY,¹ VERA LYAKHOVITSKAYA,¹ ROBERT TRIBOULET,² and DAVID CAHEN^1,3
1--Departments of Materials & Interfaces and of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel 76100. 2--CNRS LPS Bellevue, Meudon, France. 3--Author to whom corresondence should be addressed.

KEY WORDS Diffusion, electromigration, mercury cadmium telluride

The diffusion and electromigration of Ag in crystals of Cd_xHg_1-xTe is studied, as a function of original doping level and of the concentration of mercury. In materials with x = 0.55-0.8, Ag dopes p-type, when diffusing in at <125°C. This should be contrasted to what is found in n-CdTe, where in-diffusion of Ag at 200°C increases the net donor density, leaving the material n-type. Our results show that the higher is the mercury content or the hole concentration in Cd_xHg_1-xTe (x = 0.55-0.8), the faster Ag will diffuse in these materials. We explain our results, building on earlier suggestions made for Hg-rich materials, by assuming that silver diffuses by way of a substitutional-interstitial mechanism; i.e., it is present as two species with opposite charge, one of which dominates and is practically immobile, while the minority species diffuses rapidly. These forms equilibrate, at room temperature, within a few seconds, something that can be understood by postulating silver-mercury complex formation. If both forms of silver are bound to mercury, then this hypothesis explains the strong influence of mercury content on the diffusion behavior.

Characteristics of PECVD Grown Tungsten Nitride Films as Diffusion Barrier Layers for ULSI DRAM Applications
BYUNG LYUL PARK,¹ DAE-HONG KO,² YOUNG SUN KIM,¹ JUNG MIN HA,¹ YOUNG WOOK PARK,¹ SANG IN LEE,¹ HYEON-DEOK LEE,¹ MYOUNG BUM LEE,¹ U. IN CHUNG,¹ YOUNG BUM KOH,¹ and MOON YONG LEE¹
1--Semiconductor R&D Center, Samsung Electronics Co., LTD, San # 24, Nongseo-Lee, Kiheung-Eup, Yongin-City, Kyungki-Do, 449-900, Korea. 2--Semiconductor R&D Center, Samsung Electronics Co., LTD, San # 24, Nongseo-Lee, Kiheung-Eup, Yongin-City, Kyungki-Do, 449-900, Korea. Current Address: Department of Ceramic Engineering, Yonsei University, Seoul.

KEY WORDS Diffusion barrier, plasma enhanced chemical vapor desposition (PECVD), tungsten nitride, ultra large scale integration (ULSI) DRAM

We have developed tungsten nitride (W-Nitride) films grown by plasma enhanced chemical vapor deposition (PECVD) for barrier material applications in ultra large scale integration DRAM devices. As-deposited W-Nitride films show an amorphous structure, which transforms into crystalline, -W₂N and -W phases upon annealing at 800°C. The resistivity of the as-deposited films grown at the NH₃/WF₆ gas flow ratio of 1 is about 160 µ-cm, which decreases to 50 µ-cm after an rapid thermal annealing treatment at 800°C. In the contact holes with the size of 0.35 µm and aspect ratio of 3.5, the bottom step coverage of the tungsten nitride films is about 60%, which is about three times higher than that of collimated-TiN films. We obtained contact resistance and leakage current with the tungsten nitride barrier layer comparable to those with conventional collimated TiN films. The contact resistance and leakage current are stable upon thermal stressing at 450°C up to 48 h.

Accurate Determination of the Band-Offset of a Quantum Semiconductor Structure from Its Capacitance-Voltage Profile: Application to an InP/Ga_0.47In_0.53As/InP Single Quantum Well
C. GUILLOT,¹ M. DUGAY,¹ F. BARBARIN,¹ V. SOULIÈRE,² P. ABRAHAM,² and Y. MONTEIL²
1--Laboratoire des Sciences et Matériaux pour l'Electronique, et d'Automatique, URA 1793 du CNRS, Université Blaise Pascal, Clermont-ferrand II, 63177 Aubière Cedex, France. 2--Laboratoire de Physicochimie Minérale, URA 116 du CNRS, Université Claude Bernard, 69622 Villeurbanne Cedex, France.

KEY WORDS Capacitance-voltage (C-V) profiling, conduction band offset, Ga0.47In0.53As/InP, quantum well

We discuss the possible analysis of an electron distribution obtained by capacitance-voltage profiling for the determination of the conduction band offset of a single quantum well. We show that, for this method which requires only relatively light experimental equipment, a nonconsuming computational time interpretation can be set up within a quite satisfactory degree of accuracy. As an application, we report the study of a lattice matched InP/Ga_0.47In_0.53As/InP quantum well for which we get E_c = (200±10) meV, in good agreement with other measurements upon this system.