Hot electron microbolometers based on GaN heterostructures for THz applications

Microbolometers based on two dimensional electron gas (2DEG) medium in GaN semiconductor were fabricated and characterized. Low contact resistance (below 0.5 Ω·mm) achieved in our devices ensures that the THz voltage primarily drops across the active region. Due to small electron momentum relaxation time, the inductive part of the impedance in our devices is small, so these sensors can be combined with standard antennas or waveguides. Optical transmission measurements of the GaN heterostructures indicate that the 2DEG has significant coupling to the THz radiation due to Drude absorption up to frequencies well above 3 THz (100 cm⁻¹) caused by high electron concentration (∼1–4 × 10¹³ cm⁻²) and short momentum relaxation time (∼10⁻¹² sec). The normalized terahertz responsivity level defined as (dJ/J)/P is estimated to be 1.2×10⁻² W⁻¹ at 1.84 THz with dR/dT of ∼3Ω/K at room temperature in our device.