Optoelectronic materials for advanced IR sensing should combine wide strong electron coupling to the IR radiation, spectral tunability, adjustable dynamic range, manageable trade-off parameters, such as the noise characteristics and the operating time. Modern nanomaterials based on quantum dots and quantum wells provide wide possibilities to manage photoelectron processes via tuning the charge of quantum dots and quantum wells by the electric field and/or optical pumping. Variations in charge built in dots and wells change spectral characteristics, photocarrier lifetimes, and noise processes. These effects are especially strong in nanomaterials with strong selective doping of dots and wells. Manageable built-in charge provides wide possibilities to control the spectra, detector responsivity, and recombination processes.
We present the results of design, fabrication, and characterization of the room-temperature, low electron heat capacity
hot-electron THz microbolometers based on two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures. The
2DEG sensor is integrated with a broadband THz antenna and a coplanar waveguide. Devices with various patterning of
2DEG have been fabricated and tested. Optimizing the material properties, geometrical parameters of the 2DEG, and
antenna design, we match the impedances of the sensor and antenna to reach strong coupling of THz radiation to 2DEG
via the Drude absorption. Testing the detectors, we found that the THz-induced photocurrent, ΔI, is proportional to the
bias current, I, and the temperature derivative of the resistance and inversely proportional to the area of 2DEG sensor, S.
The analysis allowed us to identify the mechanism of the 2DEG response to THz radiation as electron heating. The
responsivity of our sensors, normalized to the bias current and to unit area of 2DEG, R*= ΔI•S/ (I∙P), is ~ 103 W-1 μm2.
So, for our typical sensor with an area of 1000 μm2 and bias currents of ~ 10 mA, the responsivity is ~ 0.01 A/W. The
measurements of mixing at sub-terahertz frequencies showed that the mixing bandwidth is above 2 GHz, which
corresponds to a characteristic electron relaxation time to be shorter than 0.7 ps. Further decrease of the size of 2DEG
sensors will increase the responsivity as well as allows for decreasing the local oscillator power in heterodyne