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

Abstract

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.