For the ternary semiconductors the low field mobility is
composed according to the Matthiesen rule with a bowing correction.
(3.40)
This concept is useful, if the two mobilities to
combine are of similar magnitude. For InAlAs, however, in a one-valley modeling approach the
binary mobilities to combine differ by two orders of magnitude. In this case,
(3.42) can supply negative mobility values for certain
parameter combinations of bowing parameters, doping, temperature, and material composition.
In Fig. 3.4 a one-valley approach is also given, which shows the significant disagreement with the available
data at = 0.52.
Fig. 3.3 shows the comparison of measurements,
MC data and the composition dependent analytical low field mobility model for
AlGaAs. The figures illustrate the improvement of the two valley modeling concept, since any one-valley bowing approach for electrons
will either neglect certain compositions, where the mobility gets negative, to allow a precise fit of other compositions, or will
deliver completely wrong values. The data are taken from [304].
For holes it was found, that a one-valley approach can fit the available data with sufficient accuracy.
Fig. 3.4 shows the carrier mobility for InAlAs versus
material composition for background concentration of 10 cm.
Although InAlAs is a very important material for both InP based HEMTs and HBTs, the understanding of the properties
of InAlAs is still very poor, as can be seen in Fig. 3.4.
Table 3.15 supplies the bowing parameters for (3.42).
Table 3.15:
Bowing parameters for ternary alloys for harmonic bowing in (3.42).
Material
C
C
C
C
[cm/Vs]
[cm/Vs]
[cm/Vs]
[cm/Vs]
AlGaAs
180
-250
1e6
1e6
InGaAs
1e6
1e6
-
1e6
InAlAs
1e6
1.5e8
1e6
1e6
AlGaN
1e6
1e6
-
1e6
Figure 3.5:
Carrier mobility as a function of
material composition for InGaAs at
= 300 K.
Fig. 3.5 shows the material dependence of the mobility in InGaAs. The simple quadratic bowing approach
applies for the low field mobility shown for the whole material composition. The experimental data to compare are Hall
data taken from HEMTs from the AlGaAs/InGaAs and the InAlAs/InGaAs materials system.
The data for the pseudomorphic HEMTs are taken from [77] and [79]. For the metamorphic HEMTs grown on GaAs
the data are taken from [314] and the compilation of
[113], the data for InP based devices are taken from [322]. If a double channel concept is applied, a weighted
average is determined for . It can be seen that the metamorphic devices reach similar mobility values as
the corresponding InP devices.
In Fig. 3.6 the comparison of MC data, measurements, and
the analytical model for InAlAs as a function of doping is shown. The data are taken from
the compilation of Littlejohn et al. in [163] and selectively from Goto et al. in [105]. By using a special
value for AlAs, given in Table 3.13 suitable for InAlAs only, very good agreement is achieved in Fig. 3.6.
The problem of possibly negative mobility values in (3.42) can be overcome with the bowing parameter in Table 3.15,
without having to apply a second material composition concept for the ternary alloys
in the simulator, as e.g. suggested by Sotoodeh et al. in [273].
Figure 3.6:
Comparison of the analytical
model, measurement, and MC data for InAlAs
versus doping concentration at
= 300 K
[105,163].
Figure 3.7:
Comparison of the analytical model,
measurements, and MC data for InGaAs versus
doping concentration at
= 300 K.
In Fig. 3.7 a similar comparison for InGaAs is given. The figure stresses the
importance of the residual background concentration for the low field properties [191].
To allow for the simulation of metamorphic and
pseudomorphic HEMTs on InP substrate, MC simulations have been
performed for 0.52 to support the available MC
investigations in [120] and data compiled
in [163].
Next:3.2.5.3 High Field MobilityUp:3.2.5 Carrier Mobility Previous:3.2.5.1 Low Field MobilityQuay
2001-12-21