JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 24, Number 2, February 1995 This Month Featuring: Regular Issue Papers.View February 1995 Table of Contents.

REGULAR ISSUE PAPERS

KEY WORDS Chemical beam epitaxy (CBE), GaAs, Hall measurement, reflection high-energy electron diffraction (RHEED), trisdimethylaminoarsenic, secondary ion mass spectroscopy (SIMS)

The growth of GaAs by chemical beam epitaxy using triethylgallium and trisdimethylaminoarsenic has been studied. Reflection high-energy electron diffraction (RHEED) measurements were used to investigate the growth behavior of GaAs over a wide temperature range of 300-550°C. Both group III- and group V induced RHEED intensity oscillations were observed, and actual V/III incorporation ratios on the substrate surface were established. Thick GaAs epitaxial layers (2-3 µm) were grown at different substrate temperatures and V/III ratios, and were characterized by the standard van der Pauw-Hall effect measurement and secondary ion mass spectroscopy analysis. The samples grown at substrate temperatures above 490°C showed n-type conduction, while those grown at substrate temperatures below 480°C showed p-type conduction. At a substrate temperature between 490 and 510°C and a V/III ratio of about 1.6, the unintentional doping concentration is n ~2 x 10¹⁵ cm^-3 with an electron mobility of 5700 cm²/V · s at 300K and 40000 cm²/V · s at 77K.

Selenium Doping of GaInP by Atomic Layer Epitaxy
D. JUNG,¹* M. LEONARD,² N.E. EL-MASRY,² and S.M. BEDAIR²
1--Department of Physics, North Carolina State University, Raleigh, NC 27695-8202. 2--Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911. *Present address: Laser Diode Laboratory, Samsung Advanced Istitute of Technology, P.O. Box 111, Suwon 440-600, South Korea.

KEY WORDS Atomic layer epitaxy (ALE), GaAs, GaInP, selenium (Se)

Selenium doping of GaInP was performed using atomic layer epitaxy. The dependence of the n-type carrier concentration of Se-doped GaInP on growth temperature was quite different from that of Se-doped GaAs. Reducing growth temperature was found to be a crucial factor in achieving high n-type doping levels in as-grown Se-doped GaInP.

The Thermal Stability of Ohmic Contact to n-type InGaAs Layer
J.W. WU,¹ C.Y. CHANG,¹ K.C. LIN,¹ E.Y. CHANG,² J.S. CHEN,² C.T. LEE³
1--Institute of Electronics, National Chiao Tung University, Hsinchu, Taiwan, Republic of China. 2--Institute of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China. 3--Institute of Optical Sciences, National Central University, Chung-Li, Taiwan, Republic of China.

KEY WORDS InGaAs, ohmic contact, specific contact resistance, thermal stability

The thermal stability of ohmic contact to n-type InGaAs layer is investigated. When Ni/Ge/Au is used as the contact metal, the characteristics of the ohmic contact are degraded after thermal treatment. The specific contact resistance of (Ni/Ge/Au)-InGaAs ohmic contact after annealing at 450°C is about 15 times larger than that of as-deposited sample. This is due to the decomposition of InGaAs and the interdiffusion of Ga and Au. A new phase of Au₄In appears after annealing at 300°C. While in the case of Ti/Pt/Au, Au does not penetrate into the InGaAs layer as revealed by secondary ion mass spectroscopy. The specific contact resistance of (Ti/Pt/Au)-InGaAs ohmic contact after annealing at 450°C is eight times larger than that of as-deposited sample. Therefore, the thermal stability of (Ti/Pt/Au)-InGaAs ohmic contact is better than that of (Ni/Ge/Au)InGaAs ohmic contact.

Thermal Stability of Sputter-Deposited ZnO Thin Films
Y. SONG, E.S. KIM and A. KAPILA
Department of Electrical Engineering, University of Hawaii at Manoa, Honolulu, HI 96822.

KEY WORDS Piezoelectric thin films, thermal stability

This paper describes our investigation on the thermal stability of sputter-deposited, piezoelectric, ZnO thin films, using x-ray photoelectron spectroscopy (XPS), capacitance-voltage (C-V) measurements of metal-insulator-semiconductor structures, and electron microprobe. We focus on out-diffusion of Zn from ZnO thin films at a high temperature (450°C) and the composition change of zinc and oxygen after high temperature annealing (up to 700°C), since these factors are related to reliability and integrated circuits-process-compatibility of the ZnO films which are being used increasingly more in microtransducers and acoustic devices. Our experiments with electron microprobe show that ZnO thin films sputter-deposited from a ZnO target in a reactive environment (i.e., with O₂) are thermally stable (up to 700°C). Additionally, the out-diffusion of zinc atoms from the ZnO films at a high temperature (460°C) is verified to be negligible using the XPS and C-V measurement techniques. The usage of a compound ZnO target, reactive environment with O₂ and optimized deposition parameters (including gas ratio and pressure, substrate temperature, target-substrate distance and rf power, etc.) is critical to deposit thermally stable, high quality ZnO films.

Differential Photo-Voltage Spectroscopy for Characterizing Epitaxial Multilayered and Quantum Well Structures
S. AHMAD TABATABAEI, AGIS A. ILIADIS, and COLIN E.C. WOOD
Joint Program for Advanced Electronic Materials, Electrical Engineering Department, University of Maryland and Laboratory for Physical Sciences, College Park, MD 20742.

KEY WORDS Ellipsometry, excitor transitions, molecular beam epitaxy, photo-voltage spectroscopy

An improved photo-voltage spectroscopy (PVS) technique, capable of accurately characterizing multilayered and quantum well structures, is presented. The technique is developed by noise reduction and differentiation of the photo-voltage signal which improves the accuracy and sensitivity of the standard photo-voltage spectroscopy dramatically. The resulting differential-photo-voltage spectroscopy is capable of measuring the energy gap (E_g) and hence the composition, of ternary and quaternary compounds in multilayered structures at room temperature, with a substantially higher degree of confidence than the standard PVS technique. Several structures have been examined successfully. Two representative AlGaAs/GaAs structures are reported here to establish the capabilities of this technique. These structures were found to provide values for E_g and Al mole fraction, in excellent agreement with both the targeted values based on reflective high-energy electron diffraction oscillations during molecular beam epitaxial growth, and the measured values from variable angle ellipsometry. Numerous excitor transitions from quantum wells are clearly resolved and shown to be in excellent agreement with the theoretically predicted ones.

Control of Low Fe Content in the Preparation of Semi-lnsulating InP by Wafer Annealing
D. WOLF, G. HIRT, and G. MÜLLER
Institut fur Werkstoffwissenschaften, LS 6, Kristallabor, Universität Erlangen-Nürnberg, Martensstrasse 7, D-91058 Erlangen, Germany.

KEY WORDS Annealing, Fe doping, InP, semi-insulating

A reproducible technique for preparing semi-insulating (SI) InP by high temperature annealing can only be achieved by controlled doping with Fe in a sufficient concentration for compensation. However, a successful and reproducible method to adjust the low Fe content has not been developed up to now. In this paper, we report two different experimental approaches to control the Fe content by using either precompensated starting material or an Fe source for doping via the vapor phase. InP wafers (2" diam) which were lightly predoped with Fe ([Fe] < 5 x 10¹⁵ cm^-3) during liquid encapsulated Czochralski (LEC) growth were converted from the semiconducting to the SI state and were subsequently analyzed by laterally resolved resistivity measurements. These wafers show high resistivity uniformity ( 1 x 10⁸ -cm) which has never previously been achieved with LEC material at such a low Fe concentration. Furthermore, we present the first results of annealing nominally undoped InP with a defined Fe source.

Photoluminescence and Photoreflectance Study of Si/Si_0.91Ge_0.09 andSi₉/Ge₆ Quantum Dots
Y.S. TANG,¹ C.M. SOTOMAYOR TORRES,¹* R.A. KUBIAK,² T.E. WHALL,² E.H.C. PARKER,² H. PRESTING,³ and H. KIBBEL³
1--Nanoelectronics Research Centre, Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ, United Kingdom. 2--Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom. 3--Daimler Benz AG, Research Center, Wilhelm-Runge-Strasse 11, 89081 Ulm, Germany. Royal Society of Edinburgh Research Fellow.

KEY WORDS Photoluminescence, photoreflectance, quantum dots, Si/SiGe

Nanometer-scale quantum dots based on a series of Si/Si_0.91Ge_0.09 strained layer superlattices and a Si₉/Ge₆ strain-symmetrized superlattice were fabricated using electron beam lithography and reactive ion etching. They were investigated by photoluminescence and photoreflectance. It was found for the first time that the quantum efficiency of optical emission from the quantum well layers increased by over two orders of magnitude when the quantum dot sizes were reduced to 100 nm.

Submicron Nickel Filaments Made by Electroplating Carbon Filaments as a New Filler Material for Electromagnetic Interference Shielding
XIAOPING SHUI and D.D.L. CHUNG
Composite Materials Research Laboratory, Furnas Hall, State University of New York at Buffalo, Buffalo, NY 14260-4400.

KEY WORDS Composites, electromagnetic interference, filaments, fibers, nickel, shielding

Short nickel filaments of diam 0.4 µm and containing 94 vol% Ni and 6 vol% C were fabricated by electroplating with nickel 0.1 µm diam catalytically grown carbon filaments. The use of these filaments in polyether sulfone in amounts of 3, 7, 13, and 19 vol% gave composites with electromagnetic interference shielding effectiveness at 1-2 GHz of 42, 87, 84, and 92 dB, respectively, compared to a value of 90 dB for solid copper. Less shielding was attained when 0.1 µm diam carbon filaments or 2 or 20 µm diam nickel fibers were used instead.