Hydrogen-related Levels Research Articles

Radiation Defects and Thermal Donors Introduced in Silicon by Hydrogen and Helium Implantation and Subsequent Annealing

The effect of high-energy hydrogen and helium implantation and subsequent annealing on generation of radiation defects and shallow donors in the low-doped oxygen-rich FZ n-type silicon was investigated. Samples were implanted with 7 MeV 4He2+ or 1.8 MeV 1H+ to fluences ranging from 1x109 to 3x1011 cm-2 and 1.4x1010 to 5x1012cm-2, resp., and then isochronally annealed for 30 minutes in the temperature range up to 550°C. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when annealing temperature exceeds 375°C, i.e. when the majority of vacancy-related recombination centers anneals out. The excess concentration of TDs is proportional to the helium fluence and peaks at 1.6x1014cm-3 if annealing temperature reaches 475°C. Proton irradiation itself introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Formation and annealing of shallow and deep hydrogen-related levels are strongly influenced by electric field at annealing temperatures below 175°C. If annealing temperature exceeds 350°C, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by radiation enhanced TDs.

Identification of hydrogen related defects in proton implanted float-zone silicon

Hydrogen related defects in high purity n-type float zone silicon samples have been studied by means of Deep Level Transient Spectroscopy. They were introduced, as well as the characteristic vacancy-oxygen (VO) and divacancy (V 2 ) centers, by MeV proton implantation. Two hydrogen related defect levels were resolved at 0.32 eV and 0.45 eV below the conduction band edge (E c ). Careful annealing studies indicate strongly that a third hydrogen related level, overlapping with the singly negative charge state level of V 2 , is also present in the implanted samples. The annealing behavior of the hydrogen related defects has been compared with literature data leading to a rather firm identification. The E c -0.32 eV level originates from a VO center partly saturated with hydrogen (a VOH complex) while the E c -0.45 eV level may be ascribed to a complex involving a monovacancy and a hydrogen atom (a VH complex). The third hydrogen related defect is tentatively ascribed to a complex involving a hydrogen atom and a divacancy (a V 2 H complex).

Electrical properties of platinum-hydrogen complexes in silicon

The interaction between hydrogen and platinum is studied in n- and p-type silicon using deep-level transient spectroscopy. Hydrogen is introduced by wet-chemical etching or during crystal growth. In both cases we find that hydrogen forms only electrically active complexes with platinum. Four platinum-hydrogen related deep levels are identified: E(90) at ${\mathrm{E}}_{\mathrm{C}}$-0.18 eV, E(250) at ${\mathrm{E}}_{\mathrm{C}}$-0.50 eV, H(150) at ${\mathrm{E}}_{\mathrm{V}}$+0.30 eV, and H(210) at ${\mathrm{E}}_{\mathrm{V}}$+0.40 eV. These levels belong to at least three different platinum-hydrogen complexes. Level E(250) is identical to the so-called midgap level in Pt-doped Si, which is believed to control the minority-carrier lifetime in Pt-doped silicon. Level H(150) is an acceptor and is present both in n- and p-type samples after hydrogenation. It belongs to a platinum-hydrogen complex which contains more hydrogen atoms than the complexes responsible for the other hydrogen-related levels. Annealing at temperatures above 600 K results in a complete dissociation of all the platinum-hydrogen related defects and the substitutional platinum concentration is fully restored.