Simulations with two different setups are conducted: one with a bandgap
of 1.89 eV (effective mass 0.11m in the
valley [218]), and one with a bandgap of 0.69 eV (effective
mass of 0.04m
[219]), as summarized
in Table 3.4. Results for electron mobility as a
function of lattice temperature, free carrier concentration, and
electric field are obtained.
As a particular example, Fig. 3.8 shows the low-field
electron mobility in hexagonal InN as a function of free carrier
concentration. Results from other groups
[176],[222],[231] and various experiments
[231],[232],[233], [234]
are also included. Assessing the classical band structure model
(
=1.89 eV), we achieve an electron mobility of
4000 cm
/Vs, which is in good agreement with the theoretical
results of other groups using a similar setup [176]. Considering
the newly calculated band structure model (
=0.69 eV), a maximum
mobility of
10000 cm
/Vs is achieved.
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The corresponding scattering rates are illustrated in
Fig. 3.9. The increased mobility can be explained with the
lower effective electron mass. Polyakov et al. [221]
calculated a theoretical limit as high as 14000 cm/Vs, however their
simulation does not account for piezoelectric scattering which is the
dominant mobility limitation factor at low concentrations (see
Fig. 3.9).
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Fig. 3.10 shows the mobility as a function of concentration for various values of the polar-optical phonon scattering coefficient and the high-frequency dielectric constant. Choosing the lower value results in a much higher maximum mobility, while the dependence on the scattering coefficient is lower.
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Fig. 3.11 shows the electron drift velocity versus electric
field at 10 cm
carrier concentration. Our MC simulation
results differ compared to simulation data from other groups
[221],[223],[228],[235]
either due to piezoelectric scattering at lower fields or, at high
fields, due to the choice of parameters for the permittivity and polar
optical phonon energy (
).
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Fig. 3.12 shows our simulation results obtained with
=0.04m
and with different values of the permittivity and phonon
energy. The values
=6.7 and
=11.0 proposed in
[222] lead to lower electron
velocities. Fig. 3.13 confirms that first the polar
optical phonon scattering and then the acoustic deformation potential
and inter-valley phonon scattering rates increase with higher electric
field, and are therefore decisive for the NDM effects.
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