has been reported to form a material with high transparency, being useful for in-vitro

studies with observation on-chip of several cells process [2]. SiC compounds are trans­

parent to visible wavelengths and have been used for studies of in-vitro electrical sti­

mulation concurrently with an optical observation of SiC electrodes [2].

13.3.3 High Electron Mobility

Electron mobility could be defined as how fast an electron can move through a semi­

conductor material under an applied electric field. Therefore, the carrier mobility

(µ, Equation 13.1) is the average velocity per unit electric field, considering the intrinsic

dispersion of the electronic bands (or electronic charge, q), the effective mass (where, me

∗

for electron effective mass in n-type conductivity, and mh

∗ hole effective mass in p-type

conductivity), and the scattering time (or relaxation time, τ). The relaxation time is de­

fined as the rate of change in electron momentum as it moves through a semiconductor,

and this process can occur through different mechanisms, such as phonon scattering and

ionized impurity scattering. These scattering mechanisms can be understood through

temperature-dependent carrier mobility and concentration experiments. Additionally, the

carrier mobility and concentration are proportional to the electron conductivity, showing

the importance of high electron mobility for electronic devices.

q

m

=

(13.1)

Some WBG semiconductors have a more dispersed conduct band than the valence band,

and exhibit lower me

∗, resulting in greater n-type conductivity. In WBG oxides, such as

ZnO, the low dispersion of the valence band results in lower electron mobility (Table 13.1).

On the other hand, the III-nitride compounds have shown interesting conductive proper­

ties, highlighting the GaN-based devices. A device of the two-dimensional electron gas

(2-DEG) containing stacking layers of GaN and AlGaN generates space charges due to the

piezoelectric effects, and ultrahigh electron mobility [2]. This property enables the appli­

cation of AlGaN/GaN in high electron mobility transistors (HEMT), and especially field-

effect transistors (FET) for highly sensitive biomolecular detection [2]. Further, crystalline

SiC can also exhibit excellent electron mobility, and this high conductivity has been studied

for electrodes and sensing applications, such as in neural recording electronics using 4H-

SiC, and using 3C-SiC in neural interfaces and long-lived cellular monitoring [21].

13.3.4 Biocompatibility and Biodegradability

Biocompatibility and biodegradability are crucial properties of materials to be evaluated for

bioelectronics applications. Biocompatibility of materials is the ability of a material to be

inserted or in contact with a living system without causing an adverse effect to the sur­

rounding biological environment. Therefore, a biocompatible material must be non-toxic,

non-immunogenic, non-allergenic, and non-carcinogenic. Biodegradability of a material is

the degradation of the initial compound through biological processes, which can happen

inside the living system. Additionally, in biodegradable materials, the resulting products

from the degradation also need to be compatible with the biological system. A typical

investigation of the biocompatibility of a material is through cell culture assays in vitro.

Besides all the unique electronic and optoelectronic properties of WBG materials, some

of them also exhibit excellent biocompatibility and biodegradability, enabling them for

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Bioelectronics