Absolute Pressure Dependence of the Second Ionization Level of EL2 in GaAs
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ABSOLUTE PRESSURE DEPENDENCE OF THE SECOND IONIZATION LEVEL OF EL2 IN GaAs D.E. BLISS, W. WALUKIEWICZ, D.D. NOLTE*, AND E.E. HALLER Dept. of Materials Science and Mineral Engineering, University of California at Berkeley, and the Center for Advanced Materials, Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 *Present Address: Dept. of Physics, Purdue University, West Lafayette, IN 47907 ABSTRACT We report the results of DLTS experiments under uniaxial stress on the second ionization level of EL2(++/+) in p-type GaAs. We measured the shift in the hole emission rate as a function of stress applied in the [100] and [110] directions. By modeling the valence band with two independently displacing bands and appropriately derived effective masses, we obtain a small absolute hydrostatic pressure derivative for the defect, 39 ±15 meV GPa- 1. The shear contribution is negligible. This result is very different than for the first ionization level, EL2(+/o) with a emission energy pressure derivative of 90 ±15 meV GPa-1 . The difference can be accounted for by the pressure dependence of the electron capture barrier of EL2(+/o), 49 ±15meV GPa-1 . The absolute pressure derivatives of the two levels are then comparable and in good agreement with simple theory for Ga site point defects. INTRODUCTION The fundamentally interesting property of double donor EL2 in GaAs is the metastability of the defect. By illuminating a cooled crystal, T
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