J. L. Lindström

Deep level defects in electron-irradiated 4H SiC epitaxial layers

Deep level defects in electron-irradiated 4H SiC epitaxial layers grown by chemical vapor deposition were studied using deep level transient spectroscopy. The measurements performed on electron-irradiated p+n junctions in the temperature range 100–750 K revealed several electron traps and one hole trap with thermal ionization energies ranging from 0.35 to 1.65 eV. Most of these defects were already observed at a dose of irradiation as low as ≈5×1013 cm-2. Dose dependence and annealing behavior of the defects were investigated. For two of these electron traps, the electron capture cross section was measured. From the temperature dependence studies, the capture cross section of these two defects are shown to be temperature independent.

Electronic properties of vacancy–oxygen complex in Ge crystals

It is argued that the vacancy-oxygen (VO) complex (A center) in Ge has three charge states: double negative, single negative, and neutral. Corresponding energy levels are located at E-c-0.21 eV (VO--/-) and E-v+0.27 eV (VO-/0). An absorption line at 716 cm(-1) has been assigned to the asymmetrical stretching vibration mode of the doubly negatively charged VO complex

ELECTRICALLY ACTIVE POINT DEFECTS IN N-TYPE 4H-SIC

An electrically active defect has been observed at a level position of ∼ 0.70 eV below the conduction band edge (Ec) with an extrapolated capture cross section of ∼ 5×10−14 cm2 in epitaxial layers ...

Photoluminescence of GaN: Effect of electron irradiation

The effect of electron irradiation on the optical properties of GaN material with various electrical conductivity (i.e., n type, compensated, and p type) is studied in detail by photoluminescence (PL) spectroscopy. Electron irradiation with a dose <1017 cm−2 is found to have a minor effect on photoluminescence, indicating a high radiation resistance of GaN. For higher doses, two major effects of electron irradiation on PL properties can be distinguished, i.e., radiation-induced quenching of the PL, likely caused by a radiation-induced formation of competing recombination channels, and radiation-induced formation/activation of new optically active centers.

Capture cross sections of electron irradiation induced defects in 6H–SiC

An investigation of electron irradiation induced deep levels in 6H–SiC p+n diodes grown by chemical vapor deposition has been performed. Deep level transient spectroscopy (DLTS) reveals several overlapping peaks in the temperature range 140–650 K. The electron capture cross sections have been measured by directly observing the variation of the DLTS peak height with the duration of the filling pulse and fitting the capacitance transient using multiple linear regression. Temperature dependence studies of the electron capture cross section were performed on three of the observed levels.

The oxygen dimer in Si: Its relationship to the light-induced degradation of Si solar cells?

It is widely believed that the light induced degradation of crystalline silicon solar cells is due to the formation of a BsO2i recombination center created by the optically excited migration of the oxygen dimer (charge-state-driven motion). In this letter the concentration dependence of the neutral state of O2i on [Oi] in p- and n-type Cz–Si has been determined using infrared absorption. A systematic search for the absorption signature of the dimer in the doubly positively charged state has been unsuccessful. These data strongly suggest that charge-state-driven motion (Bourgoin–Corbett mechanism) of the oxygen dimer cannot occur in typical solar silicon and hence bring into question the accepted degradation mechanism.

Deep‐level transient spectroscopy and photoluminescence studies of electron‐irradiated Czochralski silicon

Isothermal annealing of electron‐irradiated Czochralski silicon samples (n‐type) has been performed at 335 °C. The annealing process was studied using deep‐level transient spectroscopy (DLTS) and photoluminescence (PL). The dominating level in the DLTS spectra directly after irradiation is located ∼0.18 eV below the conduction band and has previously been assigned to a vacancy‐oxygen center by other authors. During the anneal the concentration of vacancy‐oxygen centers decreases, and simultaneously a new level, ∼0.20 eV below the conduction band, grows up. It is shown that the defect giving rise to this new level may be vacancy related. The PL spectra directly after irradiation are dominated by the G line (969 meV) and the C line (790 meV). The G line disappears rapidly, while the C line is still present after 320 min at 335 °C. During the heat treatment some new lines appear, e.g., the P line (767 meV) and a line at 950 meV. Based on the annealing kinetics, it is speculated that the 950‐meV defect may be vacancy related.

Defect reactions associated with divacancy elimination in silicon

Defect reactions associated with the elimination of divacancies (V-2) have been studied in n-type Czochralski (Cz) grown and float-zone (FZ) grown Si crystals by means of conventional deep-level transient spectroscopy and high-resolution Laplace deep-level transient spectroscopy (LDLTS). Divacancies were introduced into the crystals by irradiation with 4 MeV electrons. Temperature ranges of the divacancy disappearance were found to be 225-275 degreesC in Cz Si crystals and 300-350 degreesC in FZ Si crystals upon 30 min isochronal annealing. Simultaneously with the V-2 disappearance in Cz Si crystals a correlated appearance of two electron traps with activation energies for electron emission 0.23 eV {E(0.23)} and 0.47 eV {E(0.47)} was observed. It is argued that the main mechanism of the V-2 disappearance in Cz Si crystals is related to the interaction of mobile divacancies with interstitial oxygen atoms. This interaction results in the formation Of V2O centres, which are responsible for the E(0.23) and E(0.47) traps. Electronic properties of the V2O complex were found to be very similar to those of V-2 but energy levels of the two defects could easily be separated using LDLTS. In FZ Si crystals, a few electron traps appeared simultaneously with the V-2 annihilation. The small concentration of these traps compared with the V-2 concentration before annealing prevented their reliable identification. (Less)

Defect engineering in Czochralski silicon by electron irradiation at different temperatures

Infrared absorption studies of defect formation in Czochralski silicon irradiated with fast electrons in a wide range of temperatures (80-900 K) have been performed. The samples with different contents of oxygen (O-16, O-18) and carbon (C-12, C-13) isotopes were investigated, The main defect reactions are found to depend strongly on irradiation temperature and dose, as well as on impurity content and pre-history of the samples. Some new radiation-induced defects are revealed after irradiation at elevated temperatures as well as after a two-step (hot + room-temperature (RT)) irradiation.

Dominant recombination center in electron‐irradiated 3C SiC

Deep level defects and their role in carrier recombination processes in electron‐irradiated 3C SiC have been studied by photoluminescence (PL) and optically detected magnetic resonance (ODMR). An isotropic ODMR spectrum, with a g value of 2.0061±0.0002 and an effective electron spin S=1/2, is observed in irradiated 3C SiC films. From the spectral dependence studies of the ODMR signal, the defect is shown to be a deep level center related to a radiation‐induced PL band with a zero‐phonon line at 1.121 eV. Due to the competition between different carrier recombination channels, this ODMR spectrum can also be observed as a decrease of any other PL emissions from the sample, indicating its dominant role in recombination processes.