N. J. Pilgrim

Gunn oscillations in planar heterostructure diodes

Gunn oscillations have been observed and modelled, using a Monte Carlo method, in planar semiconductor GaAs/AlGaAs heterostructure diodes. Our simulation results support an interpretation of experimental results whereby the Gunn domains travel parallel to the semiconductor layers, as opposed to perpendicular to the layers in traditional vertical devices. Fabricated devices with contact separations of 4 µm down to 1.3 µm have been found to oscillate over a range of frequencies from 24.5 GHz to 108 GHz. These structures offer the prospect of generating frequencies further into the terahertz range and an increased ease of integration and flexibility over equivalent traditional vertical structures.

Novel planar Gunn diode operating in fundamental mode up to 158 GHz

We show the experimental realisation of fundamental mode operation of planar Gunn diode structures fabricated in GaAs/AlGaAs quantum wells. The electron density in the active channel is enhanced by positioning double delta-doping layers on either side. Small signal measurement shows that a typical device exhibits negative resistance up to 158 GHz. Using this device structure we have demonstrated a planar Gunn oscillator working at 115.5 GHz with an output power of -28 dBm.

An In 0.23 Ga 0.77 As-based pHEMT-like planar Gunn diode operating at 116 GHz

An In0.23Ga0.77As-based planar Gunn diode operating in its fundamental transit-time mode of oscillation at 116 GHz with output power of −24 dBm is demonstrated. The diode has a pseudomorhpic HEMT-like structure grown on a semi-insulating GaAs substrate. The layer design was carried out using a two-dimensional drift-diffusion model. The realized devices show considerable potential as a source of millimeter-wave and even terahertz radiation.

Multiple and broad frequency response Gunn diodes

Gunn diodes, operating in transit time mode, are usually thought of as incapable of generating power at multiple frequencies or over a broad frequency range. In this paper, we report experimental results showing that these diodes can generate power at several frequencies and, using Monte Carlo simulations of both planar and vertical devices, we offer an explanation of how this unusual behaviour may come into being and suggest possible applications for this novel device.

Vertical scaling of multi-stack Planar Gunn diodes

Planar Gunn diodes have been scaled vertically through combining multiple active epilayer stacks present in previously successful GaAs/AlGaAs devices. Comparison of results from fabricated devices with those simulated using a Monte Carlo approach suggest that while current and power output rises in such scaled designs, this is limited by significant heating which results in sub-linear scaling with the number of stacks. The presence of additional current-limiting mechanisms, such as inactive stacks, are implied if considering the higher currents produced by un-scaled designs or scaled devices at below peak temperatures.

Demonstration of the self-mixing effect with a planar gunn diode at millimeter-wave frequency

In this paper, we demonstrate the operation of a truly planar Gunn diode working as a self-oscillating mixer at millimeter-wave frequency. The Gunn diode was fabricated in a GaAs/Al0.23Ga0.77As layer structure. An initial proof-of-concept prototype yielded a measured conversion loss of around 20±2.5dB between 30 GHz and 40 GHz.