ELECTROSTATIC AND CURRENT TRANSPORT-PROPERTIES OF N+/SEMI-INSULATING GAAS JUNCTIONS

The steady-state charge-balance-related properties of semiconductor junctions between highly doped n-type epitaxial layers of GaAs and semi-insulating GaAs substrates are examined. Specific results are obtained for the three most common defect compensation mechanisms within the semi-insulating material: (i) a deep donor interacting with a shallow acceptor, typified by the case of the EL2 defect and background carbon, respectively; (ii) a shallow donor and a deep acceptor, as would occur for heavy levels of silicon and chromium; and (iii) a deep donor and a deep acceptor, as would be typical of EL2 and light levels of either chromium or a complementary antisite defect. Electrostatic properties, including Fermi-level positions, built-in potentials, asymptotic electric-field profiles, and junction capacitance are analytically derived based upon Hall/Shockley-Read models of the defect states and these are additionally compared against numerical solutions which implement the same models. Junction boundary conditions that pertain to the high-level injection case normally encountered in these junctions are also analytically derived and verified by numerical simulation. Limitations on the applicability of standard step-profile p-n-junction theory are discussed, as are necessary considerations for proper numerical modeling.