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The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental modethe shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600nm and 700nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In0.53Ga0.47As on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 µW was obtained from a 600 nm long ×120 µm wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible -the Monte Carlo model used predicts power output at frequencies over 300 GHz.

HighlightsWe report the development of a custom designed MEMS micro-hotplate capable of operating at high temperatures (up to 700 ̊C).The MEMS micro-hotplate can be directly mounted in a slide holder of a fluorescent confocal microscope.Temperature-sensitive nanosensors (550 nm diameter) were synthesised by covalently linking rhodamine B to a silica sol–gel matrix.Nanosensors were thermo-optically characterised using the MEMS device and confocal microscopy.The temperature dependent fluorescence response of the nanosensors was found to operate over wide range, up to 145 ̊C.

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