Deep center related to hydrogen and carbon in p-type silicon

Abstract

We have found a hole trap related to hydrogen and carbon in p-type crystalline silicon after hydrogen and deuterium injection by chemical etching and plasma exposure. It was found from deep-level transient spectroscopy that this center is located at 0.33 eV above the valence band and shows no Poole–Frenkel effect in electric fields lower than 6×103 V/cm. The depth profiling technique using deep-level transient spectroscopy indicated that this center is distributed over the range 1–7 μm from the surface with densities of 1011–1013 cm−3, depending on the hydrogenation method. On the other hand, secondary ions mass spectroscopy revealed that the majority of deuterium injected into silicon exists within a much shallower region less than 60 nm from the surface with higher densities of 1018–1020 cm−3. We have therefore concluded that the majority of injected hydrogen stays in the near-surface region probably in the form of a molecule and larger clusters and only the minority diffuses into the bulk in an atomic form to form an electrically active complex with carbon. We performed annealing experiments to investigate the thermal stability of the complex. It was stable in the dark up to 100 °C, above which it was completely annihilated in first-order kinetics with an activation energy of about 1.7 eV. The illumination of band gap light with and without a reverse bias at room temperature and at 50 °C induced no effect on the stability of the trap. This is contrast to the photoinduced annihilation of a recently observed electron trap related also to hydrogen and carbon and with comparable thermal stability in n-type silicon. These similarities and differences between the two traps and the comparison of the present results with the recently published theoretical calculations of the total energy of hydrogen configurations in the hydrogen-carbon complex suggest that the previously observed electron trap and the presently observed hole trap arise from two different defects with similar origins and structures and are tentatively ascribed to the electronic states of ‘‘bond-centered’’ and ‘‘anti-bonding of carbon’’ configurations of hydrogen in the hydrogen-carbon complex, respectively.