Nature and distribution of electrically active defects in Si-implanted and lamp-annealed GaAs

The nature and spatial distribution of deep levels arising from defects in device-quality, Si-implanted, and lamp-annealed liquid encapsulated Czochralski GaAs have been investigated. The best activation and mobility values are obtained for annealing times and temperatures of 3–5 s and 900–950 °C, respectively. Further improvements are obtained for a two-step annealing in which a second step at 840–850 °C for 15–40 s follows the main anneal step. From Hall measurements, average layer mobilities of 4000 cm2/V s and activation of 55–65% are obtained for a Si+ dose of 6.5×1012 cm−2 at 100 keV. Electrically active deep-level traps were studied by sensitive deep-level transient spectroscopy (DLTS) and optical DLTS techniques. A dominant 0.57-eV electron trap, which is also present in furnace-annealed GaAs, originates from implantation damage and is possibly related to VGa. Additional electron traps with activation energies of 0.35 and 0.40 eV are present only in lamp-annealed GaAs. Commonly observed hole traps have activation energies of 0.27–1.1 eV. The origins of these centers are discussed. Trap densities in single-step lamp-annealed samples are extremely low in comparison with furnace-annealed samples. Typical values of NT/n are 10−2–10−4. Concentrations are even lower in samples undergoing two-step annealing. The spatial variation of trap density seems to be principally determined by the variation of defect density in the substrate. It is apparent that high-quality implanted and annealed GaAs can be obtained by the two-step lamp annealing procedure.