Schedule Sep 15, 2017
Bandwidth Measurements of NbN HEB Devices on Si with GaN Buffer Layers
Nicholas Rommelfanger, Mentor Boris Karasik (JPL NASA)

Hot electron bolometers (HEBs) made of thin films of superconducting NbN are commonly used as far-infrared (THz) heterodyne detectors. The intermediate frequency (IF) bandwidth of a detector is limited by the rate of heat transfer away from the device. Detectors were fabricated from NbN on a GaN buffer layer, instead of a conventional MgO buffer, in hopes of forming a better acoustic impedance match with the NbN and decreasing the phonon escape time. Acoustic matching has previously shown promising results with MgB2 films. Devices on both GaN and MgO were tested with frequencies of 15-22 GHz near Tc = 13.5 K. Results yielded an IF bandwidth for NbN on GaN of approximately 2.8 GHz and of approximately 1.8 GHz for NbN on MgO. These results contrast with a publication that measured IF bandwidth of 7.5-8 GHz for NbN HEBs on GaN. It is believed that smaller devices used in the aforementioned publication resulted in electron diffusion through the contacts, decreasing escape time. The larger devices used in this experiment show no significant bandwidth improvement of GaN over MgO for application in THz HEB detectors.

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