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Identification of As-vacancy complexes in Zn-diffused GaAs
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Image of FIG. 1.
FIG. 1.

ToF-SIMS ion intensity of Zn over sample thickness for the as-quenched Zn-diffused SI GaAs. Zn diffusion was performed from both surfaces of the sample for 2 h at 950 °C. The diffusion is terminated by quenching the sample in RT water. The TOF-SIMS measurement was performed on the cleaved sample with a measuring area of 500 × 500 μm2.

Image of FIG. 2.
FIG. 2.

Low momentum (S) parameter as a function of the incident positron energy in SI GaAs reference sample.

Image of FIG. 3.
FIG. 3.

S parameter plotted as a function of the depth from the sample surface. The curve was compiled from the individual S(E) curves measured for the as-quenched sample and after each etching step for the same sample. The etch depths were considered as appropriate rightward shifts. The S parameter approaches the reference level at a depth of 42 μm. Therefore, this value represents the defect layer. The solid line is plotted as a smoothed curve to guide the eye.

Image of FIG. 4.
FIG. 4.

Defect profile as obtained by positron annihilation in Zn-diffused SI GaAs. The positron trapping rate is plotted as a quantity proportional to the defect concentration as a function of the depth.

Image of FIG. 5.
FIG. 5.

Temperature dependence of the average positron lifetime in Zn-diffused GaAs. The measurement is repeated after each etching step for the same sample as shown in the figure.

Image of FIG. 6.
FIG. 6.

Average and defect-related positron lifetimes and its relative intensity in Zn diffused GaAs as a function of the depth below the surface. The profile was assembled from the individual measurements for the as-quenched sample and after each etching step for the same sample measured at 300 K. The etch depths were taken into account as appropriate rightward shifts. τav approaches the reference level (bulk GaAs; dashed line) at a depth of ∼45 μm.

Image of FIG. 7.
FIG. 7.

Localized positron wave function in the As vacancy (a) and in the VAs-ZnGa complex (b) in GaAs according to the theoretical calculations. X- and Y-axis are the two spatial directions [110] and [001], respectively. The ion positions are denoted by the circles.

Image of FIG. 8.
FIG. 8.

Average positron lifetime as a function of sample temperature in SI GaAs. The sample was annealed without Zn addition for 2 h at 950 °C. Only 10 mg As were added. The annealing is terminated with quenching the sample in water. The sample is thus a reference experiment to the results shown in Fig. 5 .

Image of FIG. 9.
FIG. 9.

Results of Doppler broadening spectroscopy of Zn-diffused SI GaAs (as-quenched) and pure Zn samples. All ratio plots are normalized to SI GaAs reference sample (left part). Ratio of the momentum density to bulk GaAs for different vacancies and vacancy complexes in GaAs are theoretically calculated (right part). The curve for V As-ZnGa is in agreement with that measured in Zn-diffused GaAs. The theoretical curves are not accurate for  < 15 × 10−3 m o c (Refs. 24 and 27 ) and hence are omitted.


Generic image for table
Table I.

The results of theoretical calculations of positron lifetimes for different vacancies and vacancy complexes in GaAs for unrelaxed structures.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Identification of As-vacancy complexes in Zn-diffused GaAs