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B. Choudhuri and A. Mondal
Noise-equivalent power: The unwanted signal generated due to the random movement of the current carrier is known as noise. The noise contributes to the degradation
of information present in a signal. The noise-equivalent power (NEP) of a detector
is defined as the amount of power required to generate the same amount of noise in
a detector. It is expressed in terms of power per square root of bandwidth (W/
√
Hz).
Responsivity: The responsivity parameter represents the ability of a detector to convert the terahertz radiation into electrical entity (voltage or current). It is defined
as the ratio of the generated photocurrent/photovoltage (output) to the incident
electromagnetic power (input)
R =
I Ph
P inc
(A/W)
R =
V Ph
P inc
(V/W)
where I Ph (V Ph ) is the photocurrent (photovoltage) when light is entered into the
detector at a given wavelength, and P inc is the incident power,
Response time: Response time can be assumed as the time taken by the system to
show a change in the output signal with a change in input radiation. Generally, rise
time and fall time are the two terms those specify the speed of the optical detector
response. Rise time is the time taken by the signal to reach 90% of its maximum
value from 10% of its maximum value. Similarly, the fall time can be defined as
the time required by the detector to reach 10% of the maximum value from 90% of
the maximum value. These parameters can be measured from the radiation on–off
switching characteristics.
3 Various Types of Terahertz Detectors
In 1878, American astronomer Samuel P. Langley demonstrated the first bolometer
to measure electromagnetic power using a temperature-dependent electrical resistance [6]. Since then, the bolometers are being used dominantly to measure terahertz
radiation. Presently, with the rapid advancement of electronic device industry, the
technology is making the shift to the semiconductor-based bolometer development.
In the following section, the pioneering research work carried out on semiconductor
terahertz detector is elaborated:
Condori Quispe et al. made theoretical analysis and numerical solution of resonant tunnelling diode gated high-electron-mobility transistor for terahertz radiation
detection. AlGaN/GaN/AlGaN structure (as shown in Fig. 1) was considered for
the development of HEMT device. Maximum stable power gain was observed to be
~48 dB. This high gain was attributed to the gate-to-channel negative differential
conductance and 2-D electron gas in HEMT channel region as shown in Fig. 2 [7].
B. Choudhuri and A. Mondal
Noise-equivalent power: The unwanted signal generated due to the random movement of the current carrier is known as noise. The noise contributes to the degradation
of information present in a signal. The noise-equivalent power (NEP) of a detector
is defined as the amount of power required to generate the same amount of noise in
a detector. It is expressed in terms of power per square root of bandwidth (W/
√
Hz).
Responsivity: The responsivity parameter represents the ability of a detector to convert the terahertz radiation into electrical entity (voltage or current). It is defined
as the ratio of the generated photocurrent/photovoltage (output) to the incident
electromagnetic power (input)
R =
I Ph
P inc
(A/W)
R =
V Ph
P inc
(V/W)
where I Ph (V Ph ) is the photocurrent (photovoltage) when light is entered into the
detector at a given wavelength, and P inc is the incident power,
Response time: Response time can be assumed as the time taken by the system to
show a change in the output signal with a change in input radiation. Generally, rise
time and fall time are the two terms those specify the speed of the optical detector
response. Rise time is the time taken by the signal to reach 90% of its maximum
value from 10% of its maximum value. Similarly, the fall time can be defined as
the time required by the detector to reach 10% of the maximum value from 90% of
the maximum value. These parameters can be measured from the radiation on–off
switching characteristics.
3 Various Types of Terahertz Detectors
In 1878, American astronomer Samuel P. Langley demonstrated the first bolometer
to measure electromagnetic power using a temperature-dependent electrical resistance [6]. Since then, the bolometers are being used dominantly to measure terahertz
radiation. Presently, with the rapid advancement of electronic device industry, the
technology is making the shift to the semiconductor-based bolometer development.
In the following section, the pioneering research work carried out on semiconductor
terahertz detector is elaborated:
Condori Quispe et al. made theoretical analysis and numerical solution of resonant tunnelling diode gated high-electron-mobility transistor for terahertz radiation
detection. AlGaN/GaN/AlGaN structure (as shown in Fig. 1) was considered for
the development of HEMT device. Maximum stable power gain was observed to be
~48 dB. This high gain was attributed to the gate-to-channel negative differential
conductance and 2-D electron gas in HEMT channel region as shown in Fig. 2 [7].