174
R. N. Kini and C. P. Vaisakh
5 Structural Properties
Lattice constant: Bismuth is the largest member of group V with an atomic radius
of 230 pm. The anionic substitution of Bi necessarily leads to lattice expansion in
general due to the high lattice mismatch. X-ray diffraction studies have revealed a
definite shift in the characteristic peaks [16–18]. The studies have shown a monotonic
increase in lattice constant with increasing Bi content in the case of GaAs. The lattice
parameter data obtained from the XRD technique is often used to assess the Bi content
in the alloy with the help of Vegard’s law.
Crystallinity: The researchers always struggle with creating highly crystalline
bismide alloys with large bismuth content. The anion mismatch is one of the important
reasons, and the lattice expansion makes it difficult to achieve a lattice matching with
the substrate [19].
6 Optoelectronic Properties
Bandgap: At dilute concentrations, Ga containing III–V: Bi alloys display a linear
decrease in the bandgap [20]. In the case of GaSb 1−y Bi y , the reduction happens at a
rate of 30–40 meV/% of Bi [21, 22]. As the disparity between the anions increases,
as in the case of the GaAs 1−x Bi x system, the bandgap drop is more pronounced and
happens at a rate of ~80–90 meV/% of Bi [18, 23–26]. Many theoretical approaches
have predicted bandgap bowing effects in III–V systems. Quantum dielectric theory
[27], tight-binding method [28], DFT [22], virtual crystal approximation (VCA) [27],
band anticrossing model (BAC) [29], etc., are the main theoretical approaches used
to model the bandgap reduction with Bi incorporation in III–V semiconductors. Out
of these, the BAC model fits well with the GaAsBi system, and a combination of
BAC and VCA models provides a satisfactory explanation for the observed bandgap
reduction in GaSbBi (Fig. 2).
Large spin–orbit splitting energy: The large spin–orbit splitting in III–V semiconductors doped with bismuth is also due to valance band anticrossing. The interaction
of electron spin–orbital angular momentum with heavy Bi atom leads to the shift
of the spin–orbit band of the new system to lower energy. This phenomenon, along
with the movement of the valance band to higher energy, results in large spin–orbit
splitting [24, 26, 33]. Such effects are useful for applications in spintronics.
7 Transport Properties
Unintentional doping: Bi-related states appear close to the valence band maxima
of the host semiconductor, which in turn mainly affects the hole transport in the
bismide alloys. One of the most crucial characteristics in all the gallium-containing
R. N. Kini and C. P. Vaisakh
5 Structural Properties
Lattice constant: Bismuth is the largest member of group V with an atomic radius
of 230 pm. The anionic substitution of Bi necessarily leads to lattice expansion in
general due to the high lattice mismatch. X-ray diffraction studies have revealed a
definite shift in the characteristic peaks [16–18]. The studies have shown a monotonic
increase in lattice constant with increasing Bi content in the case of GaAs. The lattice
parameter data obtained from the XRD technique is often used to assess the Bi content
in the alloy with the help of Vegard’s law.
Crystallinity: The researchers always struggle with creating highly crystalline
bismide alloys with large bismuth content. The anion mismatch is one of the important
reasons, and the lattice expansion makes it difficult to achieve a lattice matching with
the substrate [19].
6 Optoelectronic Properties
Bandgap: At dilute concentrations, Ga containing III–V: Bi alloys display a linear
decrease in the bandgap [20]. In the case of GaSb 1−y Bi y , the reduction happens at a
rate of 30–40 meV/% of Bi [21, 22]. As the disparity between the anions increases,
as in the case of the GaAs 1−x Bi x system, the bandgap drop is more pronounced and
happens at a rate of ~80–90 meV/% of Bi [18, 23–26]. Many theoretical approaches
have predicted bandgap bowing effects in III–V systems. Quantum dielectric theory
[27], tight-binding method [28], DFT [22], virtual crystal approximation (VCA) [27],
band anticrossing model (BAC) [29], etc., are the main theoretical approaches used
to model the bandgap reduction with Bi incorporation in III–V semiconductors. Out
of these, the BAC model fits well with the GaAsBi system, and a combination of
BAC and VCA models provides a satisfactory explanation for the observed bandgap
reduction in GaSbBi (Fig. 2).
Large spin–orbit splitting energy: The large spin–orbit splitting in III–V semiconductors doped with bismuth is also due to valance band anticrossing. The interaction
of electron spin–orbital angular momentum with heavy Bi atom leads to the shift
of the spin–orbit band of the new system to lower energy. This phenomenon, along
with the movement of the valance band to higher energy, results in large spin–orbit
splitting [24, 26, 33]. Such effects are useful for applications in spintronics.
7 Transport Properties
Unintentional doping: Bi-related states appear close to the valence band maxima
of the host semiconductor, which in turn mainly affects the hole transport in the
bismide alloys. One of the most crucial characteristics in all the gallium-containing