Deep-Level Dominated Current-Voltage Characteristics of Novel Semiconductor Heterostructures
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DEEP-LEVEL DOMINATED CURRENT-VOLTAGE CHARACTERISTICS OF NOVEL SEMICONDUCTOR HETEROSTRUCTURES
K. DAS, Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907 ABSTRACT
Current-voltage characteristics of Au contacts formed on buried implanted oxide silicon-oninsulator structures and molecular beam epitaxially grown GaAs on (1012) sapphire and siliconon-sapphire substrates indicate that the dominant transport mechanism in these films is spacecharge-limited current conduction in the presence of deep-level states. The deep-level parameters, determined using an analysis of the current-voltage characteristics, appear to be sensitive to the nature of crystallographic defects present in the grown layers. Conduction in the GaAs film on SOS was dominated by one discrete state located - 0.28eV below the conduction band-edge, which is close to the El center uniquely observed in the molecular beam epitaxially grown GaAs-on-Si. Discrete levels are also observed in annealed buried implanted oxide silicon-on-insulator films. In contrast, the GaAs films deposited directly on (1012) sapphire substrates and rapid-thermally annealed high-dose As implanted buried oxide SOI films appear to have a continuous distribution of states. The distributed states in GaAs films deposited directly on sapphire probably arise from the electrical activity of the double-position boundaries present in this material system. INTRODUCTION Heteroepitaxial GaAs films have received a great deal of attention for the potential monolithic integration of optoelectronic and electronic devices [1]. The advantages of insulating sapphire and silicon-on-insulators (SOI) such as silicon-on-sapphire (SOS) and buried implanted oxide structures in silicon are potentially numerous and include: (1) dielectric isolation, (2) extreme radiation hardness, and (3) the excellent physical,and optical transmission properties afforded by sapphire. The present study involves an assessment of the electrical characteristics of the material systems utilizing photolithographically-defined metal-semiconductor contacts. The currentvoltage (I-V) characteristics of these contacts indicate that the dominant transport mechanism is space-charge-limited current conduction and is influenced by the presence of deep-level states. An analysis of the I-V characteristics has been employed to determine the position and concentration of the deep states in implanted oxide SOI and heteroepitaxial GaAs films deposited on (1012) sapphire and silicon-on-sapphire (SOS) substrates. The procedure, as outlined below, can serve as a technique for the rapid electrical assessment of the films prior to device fabrication. EXPERIMENTAL PROCEDURE GaAs films have been grown directly on (1012) sapphire and commercially-available chemical vapor deposited (CVD) (100) silicon-on-sapphire (SOS) substrates by molecular beam epitaxy (MBE) under identical growth conditions [2]. The native oxide present on the SOS sample was desorbed by heating the substrates to a tem
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