JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 25, Number 12, December 1996 This Month Featuring: Regular Issue Papers. View December 1996 Table of Contents.

REGULAR ISSUE PAPERS

KEY WORDS (AlP)n(GaP)n, metalorganic vapor phase epitaxy (MOVPE), photoluminescence (PL), short-period superlattice, strained layers

Biaxial tensile strain is introduced into (AlP)_n(GaP)_n superlattices (SLs) by growing the SLs on slightly lattice-mismatched InGaP intermediate layers on GaP(001) substrates. A significant enhancement of photoluminescence intensity is observed for the strained (AlP)_n (GaP)_n short-period SLs, especially for those with n ¾= 3.

Patterning of Transparent Conducting Oxide Thin Films by Wet Etching for a-Si:H TFT-LCDs
JE-HSIUNG LAN¹ JERZY KANICKI,¹ ANTHONY CATALANO,² JAMES KEANE,² WILLEM DEN BOER,³ and TIEER GU³
1--Center for Display Technology and Manufacturing, University of Michigan, Ann Arbor, MI 48105-2551. 2--National Renewal Energy Laboratory, Golden, CO. 3--Optical Imaging Systems Inc., Northville, MI 48084.

KEY WORDS Al-doped zinc oxide, etching, films, hydrogen containing plasma, indium tin oxide

The patterning characteristics of the indium tin oxide (ITO) thin films having different microstructures were investigated. Several etching solutions (HCl, HBr, and their mixtures with HNO₃) were used in this study. We have found that ITO films containing a larger volume fraction of the amorphous phase show higher etch rates than those containing a larger volume fraction of the crystalline phase. Also, the crystalline ITO films have shown a very good uniformity in patterning, and following the etching no ITO residue (unetched ITO) formation has been observed. In contrast, ITO residues were found after the etching of the films containing both amorphous and crystalline phases. We have also developed a process for the fabrication of the ITO with a tapered edge profile. The taper angle can be controlled by varying the ratio of HNO₃ to the HCl in the etching solutions. Finally, ITO films have been found to be chemically unstable in a hydrogen containing plasma environment. On the contrary, aluminum doped zinc oxide (AZO) films, having an optical transmittance and electrical resistivity comparable to ITO films, are very stable in the same hydrogen containing plasma environment. In addition, a high etch rate, no etching residue formation, and a uniform etching have been found for the AZO films, which make them suitable for a-Si:H TFT-LCD applications.

Au/Ge/Pd Ohmic Contacts to n-GaAs with the Mo/Ti Diffusion Barrier
CHUN-YI CHAI,¹ JUNG-A HUANG,¹ YONG-LIN LAI,¹ JANNE-WHA WU,¹ CHUN-YEN CHANG,¹ YI-JEN CHAN,² and HUANG-CHUNG CHENG¹
1--Department of Electronics Engineering and Institute of Electronics, Semiconductor Research Center, National Chiao-Tung University, Hsinchu, Taiwan, Republic of China. 2--Department of Electrical Engineering, National Central University, Chungli, Taiwan, Republic of China.

KEY WORDS Au/Mo/Ti/Ge/Pd metallization, n-type GaAs, ohmic contact

The influences of the As-outdiffusion and Au-indiffusion on the performances of the Au/Ge/Pd/n-GaAs ohmic metallization systems are clarified by investigating three different types of barrier metal structures Au/Ge/Pd/GaAs, Au/Ti/Ge/Pd/GaAs, and Au/Mo/Ti/Ge/Pd/GaAs. The results indicate that As-outdiffusion leads to higher specific contact resistivity, whereas Au-indiffusion contributes to the turnaround of the contact resistivity at even higher annealing temperature. For Au/Mo/Ti/Ge/Pd/n-GaAs samples, they exhibit the smoothest surface and the lowest specific contact resistivity with the widest available annealing temperature range. Moreover, Auger electron spectroscopy depth profiles show that the existing Ti oxide for the Mo/Ti bilayer can very effectively retard Au-indiffusion, reflecting the onset of the turnaround point at much higher annealing temperature.

Cd and Te-Based Ohmic Contact Materials to p-Type ZnSe
K. HASHIMOTO,¹ Y. KOIDE,¹ O. TADANAGA,¹ T. OKU¹ N. TERAGUCHI,² Y. TOMOMURA,² A. SUZUKI,² and MASANORI MURAKAMI³
1--Department of Materials Science and Engineering, Division of Engineering Science, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan. 2--Central Research Laboratories, Sharp Corporation, Ichinomoto-cho, Tenri, Nara 632, Japan. 3--Department of Materials Science and Engineering, Division of Engineering Science, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan.

KEY WORDS Cd, CdxZn1-xSe, ohmic contact, Schottky barrier, Te, turn-on voltage, ZnSe

In order to explore a possibility of forming an intermediate semiconductor layer with low Schottky barrier by the conventional deposition and annealing technique, the electrical properties of Cd and Te-based contacts on the nitrogen-doped ZnSe substrates have been investigated. Cd in the Cd/W contact reacted with the ZnSe substrate after annealing at temperatures above 250°C and formed epitaxial Cd_xZn_1-xSe layers, leading to reduction of the "turn-on" voltage (V_T) from about 11 to 6 V (here, a slash "/" between Cd and W means the deposition sequence). The reduction of the V_T value by annealing at elevated temperatures was also observed for the Bi-Cd/W and In-Cd/W contacts. The average Cd composition (x) in the Cd_xZn_l-xSe layers was measured to be larger than 0.9, which agreed with the values estimated from the calculated Cd-Zn-Se phase diagrams. The ohmic behavior was strongly influenced by the thickness of the Cd_xZn_l-xSe layer, the density of misfit dislocations formed at the interface between the Cd_xZn_1-xSe and the ZnSe, and/or the total area of the Cd_xZn_1-xSe layers covering the ZnSe surface. The present result suggests that formation of the large-areal Cd_xZn_1-xSe layers with thin thickness is crucial to achieve further reduction of the V_T value by the conventional deposition and annealing technique. Also, the V_T reduction was not obtained for the Te/W contact even after annealing at temperatures close to 300°C, which was explained to be due to absence of ternary ZnSe_1-xTe_x intermediate layers.

Capacitance Behavior of GaAs-MIS Structures with Low-Temperature Grown GaAs Dielectric
J.K. LUO,¹ D. WESTWOOD,³ H. THOMAS,² and D.V. MORGAN²
1--Cardiff School of Engineering, University of Wales, Cardiff, United Kingdom. Present address: Newport Wafer-Fab Ltd., Cardiff Road, Duffryn, Newport, Gwent NY9 1YJ, United Kingdom. 2--Cardiff School of Engineering, University of Wales, Cardiff, United Kingdom. 3--Department of Physics & Astronomy, University of Wales College of Cardiff, United Kingdom.

KEY WORDS Admittance spectroscopy, capacitance-voltage (C-V), interface potential, low temperature grown GaAs, molecular beam epitaxy (MBE), metal/dielectric/semiconductor

Low temperature (LT-) grown GaAs has been used as a dielectric in a metal/dielectric/semiconductor structure, and its capacitance behavior has been investigated by C-V_B and admittance spectroscopy. The C-V_B measurement revealed a barrier height of 0.40 eV at the interface of the LT- and n-GaAs. The capacitance-temperature profile shows a step decrease in capacitance, accompanied by a maximum conductance as the measurement temperature was decreased. The detailed investigation shows that this anomalous C-T behavior is caused by the increase of resistivity of the LT-GaAs, which leads to the formation of a metal/insulator/semiconductor structure at low temperature. This result has an impact on the application of the LT-GaAs, because it introduces a frequency dispersion to the device characteristics.

Analysis of the Infrared Transmission Data of Hydrogenated Amorphous Silicon Film Fabricated by High Rate PECVD
W. HU, FLORENCE Y.M. CHAN, D.P. WEBB, Y.C. CHAN, and Y.W. LAM
Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.

KEY WORDS Absorption, hydrogenated amorphous silicon, inhomogeneity, optical band gap, plasma enhanced chemical vapor deposition (PECVD), transmission

The optical properties of hydrogenated amorphous silicon thin films prepared by a new thermocatalytic plasma enhanced chemical vapor deposition (PECVD) method are here reported for the first time. The transmission spectrum of the film, deposited at a rate of 1.5 nm/s, was measured between 500 and 1100 nm. The envelopes of the transmission spectrum interference maxima and minima were analyzed to reveal the absorption coefficient (), the refractive index n(), the average thickness of the film (791 nm) and the variation of the thickness (11.4 nm), using an analysis which takes into account film inhomogeneity. The modified Newton's method of numerical analysis was used to obtain the optical parameters. The optical band gap ₀ was determined to be 1.69 eV from the absorption coefficient spectrum, commensurate with values quoted for lower deposition rate PECVD films. The value for ₀, the small variation of the film thickness, and a value for the defect density of 3.7 x 10¹⁵ cm^-3 determined for similar material in other work indicate that the thermocatalytic PECVD method can produce acceptable quality films at a high deposition rate.

Dislocation-Free Undoped Semi-Insulating GaAs Epilayers Prepared by Chloride Chemical Vapor Deposition and Successive Wafer Annealing
A. NODA, K. KOHIRO, and O. ODA
Electronic Materials & Components Laboratory, Japan Energy Corporation, 3-17-35, Niizo-Minami, Toda, Saitama, 335, Japan.

KEY WORDS Annealing, dislocation-free, GaAs, semi-insulating epilayer

Dislocation-free (DF) undoped semi-insulating GaAs epilayers have been realized by chloride chemical vapor deposition and successive wafer annealing. It was found that undoped conductive DF GaAs epilayers grown on Si-doped n-type DF GaAs substrates can be converted to semi-insulating by wafer annealing at temperatures higher than 950°C. The resistivity of these semi-insulating epilayers was higher than 10⁷ cm. The outdiffusion of Si from the substrate to the epilayer was analyzed by secondary ion mass spectrometry and it was found that the thickness of the outdiffusion region was only 1 um.

Influence of Boron Doping on the Properties of Amorphous and Microcrystalline SiC Films Prepared Using ECR-CVD
S.F. YOON, R. JI, and J. AHN
School of Electrical and Electronics Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore.

KEY WORDS Boron doping, ECR-CVD, Raman scattering analysis, SiC

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) method from a mixture of methane, silane, and hydrogen, with diborane as the doping gas. The effect of changes in the percentage of the diborane to reactant gas mixture on the deposition rate, optical bandgap, and photoconductivity were investigated. There is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were all amorphous and the bandgap decreases as the diborane level is increased whereas films deposited at a high microwave power of 800 W at low diborane levels are highly photoconductive and contain microcrystalline silicon inclusions. These films become amorphous as the diborane level is increased, while the optical bandgap remains relatively unaffected throughout the entire range of diborane levels investigated. The effect of the microwave power was also investigated. The conductivity increases rapidly to a maximum, followed by rapid reduction at high microwave powers. Raman scattering analysis showed evidence of the formation and increase of microcrystalline silicon inclusions and diamond-like components in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity.

Characterization of Closed Space Vapor Transport GaP Epitaxial Layers
J. MIMILA-ARROYO¹ J. DIAZ,¹ M.B. DERBALI,² H. MAAREF,² S. ALAYA,² D. STIEVENARD,³ and J.C. BOURGOIN⁴
1--Centro de Investigacion y de Estudios Avanzados del I.P.N., Av. Instituto Politécnico Nacional 2508, Col. San Pedro Zacatenco, México, D.F., C.P. 07300, Mexico. 2--Département de Physique, Faculté des Sciences de Monastir, 5000 Monastir, Tunisia. 3--Institut d'Electronique et de Micro-Electronique du Nord (IEMN), UMR CNRS 9929, Département ISEN, 41 Boulevard Vauban, 59046 Lille Cedex, France. 4--Groupe de Physique des Solides, Universités Paris 6 et Paris 7, Centre National de la Recherche Scientifique, Tour 23, 2 place Jussieu, 75251 Paris Cedex 05, France.

KEY WORDS Deep level transient spectroscopy (DLTS), epitaxy, EPR, GaP, photoluminescence (PL)

The growth of homoepitaxial GaP layers using Te-doped GaP as source material has been obtained by the so-called closed space vapor transport technique. The photoluminescence study shows that these layers, when grown under optimized thermodynamical conditions, have both a large luminescence efficiency and the same optical quality as the ones obtained by liquid phase epitaxy. The variation of the luminescence properties with the conditions of growth has been investigated. Both electron paramagnetic resonance and deep level transient spectroscopy detect the presence of deep levels that are not observed in liquid phase epitaxy materials.