VBO, amount of strain, effective mass (m*) and splitting (Δ lh-hh ) between the light hole (lh) and heavy hole (hh) offsets are important parameters for obtaining high hole mobility in III-V heterostructures.
Isoenergy surfaces for upper valence band in silicon, GaAs and InSb at 2 meV/25 meV/50 meV.
Isoenergy surface (left) and 2D energy contour along the transport plane (right) for upper valence band in GaAs for (a) biaxial compression and (b) uniaxial compression.
Calculated hole mobility for varying stoichiometries in InxGa1−xAs and InxGa1−xSb. Antimonides have twice as high hole mobility compared to arsenides.
Polar plot showing calculated hole mobility enhancement for (a) 2% biaxial strain and (b) 2% uniaxial strain. Hollow/solid symbols represent tension/compression. The substrate orientation was (100) while the angle along the plot represents the different directions along which the channel of the transistor can be oriented. For uniaxial strain, the strain was applied parallel to the transport direction.
Calculated mobility enhancement for varying amount of biaxial strain, which can be achieved during MBE growth. Positive values represent biaxial compression while negative strain represents biaxial tension.
Two different approaches for obtaining a compressively strain Sb-channel. Approach A uses an InGaSb channel and an AlGaSb barrier. Approach B utilizes a GaSb channel and an AlAsSb barrier.
Cross-section showing the different layers in a quantum-well heterostructure with (a) InxGa1−xSb and (b) GaSb channel. The AlAsxSb1−x layer is composed of a AlSb/AlAs short-period superlattice. Also shown are high resolution TEM images around the channel region.
(a) Dislocations and (b) misfit defects in the buffer layer which accommodates the large lattice mismatch between the channel and the GaAs substrate.
High Resolution XRD scans on the samples A1 (top) and B1 (bottom) near the (004) GaAs peak. For sample B1, which uses (AlAs)AlSb as the buffer, we observe main and satellite peaks characteristic of the digital superlattice.
Reciprocal lattice scan on sample B1 around GaAs (004) and(115).
VBO for sample A1 (approach A) is calculated by taking the difference in the valence band spectrum from the InxGa1−xSb channel and AlyGa1−ySb buffer.
VBO for sample B1 (approach B) is calculated by taking the difference in the valence band spectrum from the GaSb channel and the AlAsySb1−y buffer.
Hole mobility (μ h) and sheet charge (Ns) are measured as a function of temperature using Hall measurements for samples: A1, A2, A3 (top) and B1, B2 (bottom).
A high temperature anneal (600 °C/60 s) before channel growth to optimize the interface results in a large increase in low-temperature mobility but gives only a slight gain (900 cm2/Vs to 940 cm2/Vs) in mobility at 300 K.
Conductivity tensors (σxx and σxx) are measured as a function of magnetic field (B) for various temperatures. MSA on the data confirms that there is no parallel conduction in the stack and is used to estimate number of carriers in lh/hh bands and their mobility (Figure 17).
(a) Number and (b) mobility of carriers in the light (lh) and heavy hole (hh) bands as a function of temperature for sample A1.
Shubnikov-de-Haas (SdH) oscillations in sheet resistance (inset) are observed at low temperatures and high magnetic field. Temperature dependence of these oscillations is used to calculate m* (Table III).
SdH oscillations at 2 K are plotted vs. 1/B for a sheet charge of 1.1 × 1012/cm2. The oscillatory behavior is periodic in nature with a single dominant frequency, indicating that only the lh band is occupied at this sheet charge.
SdH oscillations at 2 K are plotted vs. 1/B for sheet charge of 3.5 × 1012/cm2. The oscillations are combinations of two dominant frequencies, indicating that both lh and hh bands are occupied at this sheet charge.
Hole mobility (μ h) is measured as a function of sheet charge (Ns) using gated Hall measurements. Reported values in (strained) silicon are also plotted for comparison.
Relevant properties of different semiconductor materials at 300 K. Note that III-V’s (antimonides in particular) have lower elasticity constants than silicon.
Parameters measured, technique used, and corresponding figures.
Details on the samples studied. Mobility and sheet charge (NS) at 300 K measured using Hall measurements are listed along with value of light hole effective mass measured using Shubnikov–de Haas oscillations.
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