Effect of LT GaAs on Epitaxial Al/GaAs Schottky Diode Characteristics
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EFFECT OF LT GaAs ON EPITAXIAL Al/GaAs SCHOTTKY DIODE CHARACTERISTICS KAI ZHANG* AND D. L. MILLER Center for Electronic Materials and Processing, Department of Electrical and Computer Engineering, *Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 ABSTRACT The effect of LT GaAs on the effective barrier height of the epitaxial Al/GaAs Schottky contact was investigated for the first time by inserting a thin LT GaAs layer (50 - 500A) between the in situ deposited Al film and conventional MBE GaAs epitaxial layer. The activation energy plot of saturation current for the devices showed that the effective barrier height exhibits a dependence on LT GaAs thickness and reaches a saturated barrier height when the LT GaAs layer exceeds a critical thickness. Compared to the samples which had no LT GaAs layer, the effective Schottky barrier height was decreased from 0.79 eV to 0.35 eV for the n-GaAs samples, and increased from 0.55 eV to 0.72 eV for the p-GaAs samples. The Schottky barrier height modification achieved by LT GaAs is tentatively explained in the terms of a bulk Fermi level pinning model. The work described here suggests that LT GaAs can be used as a defect source with controlled thickness to study defect associated phenomena such as Schottky barrier height modification.
1.Introduction GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures (LT GaAs) has been shown to be both electrically and optically inactive, and has been used as a buffer layer for GaAs MESFETs to eliminate backgating [1]. These properties of LT GaAs were attributed to excess arsenic incorporation due to non-stoichiometric growth at low substrate temperatures, which results in a high density of arsenic antisite (ASGa) defects[2], arsenic interstitial (Asi) defects [3] and arsenic precipitates [4, 5]. The role of defects in Schottky barrier height modification has been verified by surface processing [6-9], which introduced a defect layer near the semiconductor surface. Since LT GaAs contains a high density of defects, it may also influence the Schottky barrier height. In this work, the effect of LT GaAs on the electrical characteristics of epitaxial Al/GaAs Schottky contacts was examined for the first time by inserting a thin LT GaAs layer (50 - 500A) between the in situ deposited Al films and conventional MBE GaAs epitaxial layers. Using the LT GaAs layer as a defect region to study Schottky barrier modification offers the advantage of a defect layer of controlled thickness, which is difficult to achieve by other surface modification techniques such as ion implantation. 2. Experimental procedure Samples with the epitaxial layer structure as shown in Fig. 1 were grown in a Varian Gen II MBE system on (100) Si doped (n+) GaAs substrates cut 20 off toward (110), or normally (100)±0.50 Zn doped (p+) GaAs substrates. A LT GaAs cap layer with a thickness of 50A to 500A was grown at a reduced temperature of 3000C without changing other growth parameters. A 1500A Al film was
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