type 6H silicon carbide has been studied using positron lifetime spectroscopy with isochronal annealing temperatures of 400, 650, 900, 1200, and 1400°C. In the as-grown sample, we have identified the V Si vacancy, the V C V Si divacancy, and probably the V C vacancy. The silicon vacancy and the carbon vacancy were found to anneal out in the temperature range 400-650°C. The V C V Si divacancy was found to persist at an annealing temperature of 1400°C.
Conversion of the Au/ n-ZnO contact from Ohmic to rectifying with H 2 O 2 pretreatment was studied systematically using I-V measurements, x-ray photoemission spectroscopy, positron annihilation spectroscopy, and deep level transient spectroscopy. H 2 O 2 treatment did not affect the carbon surface contamination or the E C-0.31 eV deep level, but it resulted in a significant decrease of the surface OH contamination and the formation of vacancy-type defects ͑Zn vacancy or vacancy cluster͒ close to the surface. The formation of a rectifying contact can be attributed to the reduced conductivity of the surface region due to the removal of OH and the formation of vacancy-type defects.
Articles you may be interested in Comparison of crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te nanocrystalline thin films: Effects of homogeneous irradiation with an electron beam Electron-irradiation-induced divacancy in lightly doped silicon The recovery of the electrical resistivity and thermoelectric power in a number of n-and p-type a-tin samples, irradiated at low temperature, is considered. Three distinct first-order stages in the temperature range 20-50 K are observed. A fractional defect recovery has been deduced such that relative percentages of lA : 18 : Ie =90 : 4 : 6 anneal in the three stages. Activation energy scaling factors were found to be 69, 94, and 122 meV, respectively, for the three stages. Carrier mobilities as functions of carrier and defect concentration were calculated and found to be in good agreement with previously published values. Estimates for these quantities were also deduced when the samples were near to their intrinsic states (n. ~ nh)' A c1ose-pair-defect charge carrier trapping model provides a consistent explanation for all damage and recovery data.
It is expected from existing theories that the core level of Si nanocrystals (nc-Si) embedded in a SiO2 matrix
should shift toward a higher binding energy as compared to that of bulk crystalline Si due to quantum size
effect. Indeed, it is observed in X-ray photoemission experiments that the Si 2p core level shifts to a higher
apparent binding energy by 1−2 eV for all five oxidation states of Si
n
+ (n = 0, 1, 2, 3, and 4) in the material
system of SiO2 containing nc-Si. However, it is found that the core-level shift is due to a charging effect in
the material system. After correction for the charging effect by using C 1s binding energy due to contamination
on the SiO2 surface, the core level of the oxidation state Si4+ is the same as that of pure SiO2, whereas the
core level of the isolated nc-Si with an average size of about 3 nm shifts by ∼ 0.6 eV to a lower binding
energy as compared to that of bulk crystalline Si. It is suspected that the core-level shift of the nc-Si toward
a lower binding energy is due to the influence of the differential charging between the SiO2 surface layer and
the nc-Si underneath.
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