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Electrical characterization and modelling of n–n Ge-Si heterojunctions with relatively low interface state densities
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View: Figures


Image of FIG. 1.
FIG. 1.

Cross section transmission electron microscope (TEM) image showing the expitaxial SME Ge layer on a Si (100) substrate (Refs. 9 and 15). The inset enlarges the abrupt Si-Ge interface to visualize the regular dislocation network. In this dark field/weak beam image, the sample was rotated by .

Image of FIG. 2.
FIG. 2.

Calculated band diagram of the n–n heterojunction in thermal equilibrium at , illustrating the quantities used in the model. The parameters used for the band diagram calculation were extracted from the experimental I(V)-curves (see chapter IV).

Image of FIG. 3.
FIG. 3.

Ratios between the trap occupation probabilities according to the Fermi distribution of the Ge and the general expression according to Eq. (7) as function of the trap energy level within the Ge bandgap. Different bias conditions are shown. The vertical lines mark the respective positions of .

Image of FIG. 4.
FIG. 4.

Calculated band diagram of the n–n Si-Ge heterojunction under negative bias on Ge ( = −0.3 V), illustrating different current transport mechanism. The size of the arrowheads on each side illustrates the relative amount of capture (emission) by (from) the interface states and of thermionic emission from (to) the Si to (from) the Ge, respectively.

Image of FIG. 5.
FIG. 5.

Measured I(V)-curves of n–n Ge-Si heterojunction diode for different temperatures. is externally applied voltage on the device, which may partially drop across series resistances.

Image of FIG. 6.
FIG. 6.

Interface charge density as a function of the position of the Ge quasi Fermi level with respect to the Ge valence band edge at z = 0. All data points refer to the reverse direction −0.5 V 0 V. The and the values were extracted from the experimental I(V)-curves. Linear regression was performed within the linear regime of the curves (dashed lines).

Image of FIG. 7.
FIG. 7.

(a) Comparison of experimental (symbols) and simulated (lines) -curves for different current transport mechanisms—thermionic emission (mechanism (1)) and total trap mediated current (mechanism(2 + 3)). In the simulations, the capture cross section was varied from to . All curves refer to . (b) Single contributions to interface generation/recombination and net electron transmission from Ge to Si for and . (c) Comparison of experiment and simulations assuming the hole density in the Si to be determined by rather than by (in contrast to (a) and (b)). was fixed to .

Image of FIG. 8.
FIG. 8.

Comparison between experimental J(V)-curves (symbols) and simulated thermionic emission current (lines) for different temperatures. The experimental curves had been corrected for the voltage drop across the series resistance (neglectable in reverse direction). In the simulations, was fixed to as extracted for .

Image of FIG. 9.
FIG. 9.

Comparison of experimental C(V) curve (symbols) and simulated individual capacitive contributions (lines) for . The experimental data refer to the parallel capacitance at 10 kHz, which was calculated from the measured impedance at 10 kHz and 20 kHz within a framework of a three element equivalent circuit model (capacitance in parallel to a conductance in series with a resistor).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Electrical characterization and modelling of n–n Ge-Si heterojunctions with relatively low interface state densities