Deep Electron Traps In Mbe Gaas On Si
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DEEP ELECTRON TRAPS IN MBE GaAs ON Si
K.NAUKA, G.A.REID, S.J.ROSNER, S.M.KOCH*, and J.S.HARRIS* Hewlett Packard Laboratories, Palo Alto, CA 94304 *Stanford Electronics Lab, Stanford University, Stanford, CA 94305
ABSTRACT Deep electron traps were investigated in MBE GaAs grown directly on Si substrates with orientations a few degrees off the axis. Capacitance Deep Level Transient Spectroscopy (CDLTS) revealed the presence of eleven electron traps in the GaAs epilayer. Their activation energies ranged from 0.21 eV to 0.83 eV below the conduction band. Most of these traps were previously observed in homoepitaxial GaAs films grown under As-rich conditions (VPE, MBE), or in electron irradiated bulk GaAs. Trap concentrations tracked Si dopant density and MBE growth conditions. Observed deep levels are not introduced by metals or other contaminants present at the GaAs-Si interfaces. Rather, they are caused by defect complexes. These complexes involve native point defects, whose formation is favoured by As-rich environments, by lattice mismatch, and by different thermal expansion coefficients. Si dopant atoms may also participate in the formation of these defects. A similar deep level generation mechanism is proposed for the electron traps in homoepitaxial MBE GaAs layers.
INTRODUCTION GaAs grown directly on Si substrates (GaAs/Si) offers a variety of possibilities for generating new types of micro- and optoelectronic devices. This material combines advantages offered by the GaAs epilayer (direct gap related optical phenomena, high mobility) with the superior qualities of Si material (mechanical strength, highly advanced Si device technologies). GaAs has been grown on Si both by MBE and OMVPE techniques, and a large number of potential applications have already been demonstrated. These include MESFETs, MODFETs, LEDs, laser action at room temperature, and monolithically integrated GaAs LEDs driven by a Si MOS controller [1-5]. There are several fundamental incompatibilities of the GaAs-Si system which could hinder its further development. The most serious are: thermal expansion coefficient differences, large lattice mismatch, and antiphase disorder caused by polar on nonpolar nucleation. Intensive efforts have attempted to overcome these problems. Optimization of the growth conditions have resulted in GaAs layers with very good structural integrity and a dislocation density below 108 cm- 2 . The structural quality of GaAs/Si has been studied rather extensively. There are numerous reports correlating structural quality of GaAs/Si with growth parameters [6-9]. However, little is known about the electronic nature of defects in heteroepitaxial GaAs/Si structures. The goal of this study was to investigate deep electron traps in GaAs grown by MBE on Si substrates, and to relate them to the growth conditions.
Mat. Res. Soc. Symp. Proc. Vol. 91.
1987 Materials Research Society
226
Experimental The epilayers examined in this study were grown using Varian GenII MBE equipment. The substrates were p-type 2 inch diameter (100)
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