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The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode-the 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 1.5 μm, 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 0.5 μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600 nm and 700 nm, 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. [ABSTRACT FROM AUTHOR]

When biased in the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes. This EL is due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. The EL forms non-uniform patterns whose intensity shows short-range intensity variations in the direction parallel to the contacts and decreases along the device channel towards the cathode. This paper employs Monte Carlo models, in conjunction with the experimental data, to analyse these non-uniform EL patterns and to study the carrier dynamics responsible for them. It is found that the short-range lateral (i.e., parallel to the device contacts) EL patterns are probably due to non-uniformities in the doping of the anode contact, illustrating the usefulness of EL analysis on the detection of such inhomogeneities. The overall decreasing EL intensity towards the anode is also discussed in terms of the interaction of holes with the time-dependent electric field due to the transit of the Gunn domains. Due to their lower relative mobility and the low electric field outside of the Gunn domain, freshly generated holes remain close to the anode until the arrival of a new domain accelerates them towards the cathode. When the average over the transit of several Gunn domains is considered, this results in a higher hole density, and hence a higher EL intensity, next to the anode. [ABSTRACT FROM AUTHOR]

The measured intrinsic saturation velocity (vsi) of carriers in a gallium nitride (GaN) high electron mobility transistor (HEMT) is very much lower than that predicted using Monte Carlo simulation. A novel method of extraction of the intrinsic saturation velocity (vsi) of carriers has been developed utilising the deembedded s-parameters, thus enabling the calculation of vsi over a wide range of bias conditions. The method is equally applicable for gallium arsenide (GaAs) and indium phosphide (InP) based transistors. The measurements indicate for GaN-based HEMT a maximum deembedded saturation velocity of 1.1 × 105 m/s close to the pinchoff voltage (Vp). It was found that self-beating had only a weak effect on the saturation velocity up to junction temperatures approaching 140 °C above ambient. [ABSTRACT FROM AUTHOR]

We present the first results of a planar Gunn diode made in \In0.53\Ga0.47\As on an InP substrate, operating at a fundamental frequency up to 164 GHz. For a 120-\mu\m-wide device with a 1.3- \mu\m active channel length, the highest power achieved was approximately -10 dBm at 164 GHz. [ABSTRACT FROM AUTHOR]

Radiance and temperature profiles for the first time have been measured along the mesa side of Gunn diode samples, using an infrared microscope with a spatial resolution of 2.5 µm. Bulk heat generation occurs in the transit region, but measurements have shown a small amount of additional ohmic heating in the substrate layer, which will influence the maximum temperature of the device. The presented thermal measurements have been used to improve the existing thermal finite-element model of the diode. The measurements also represent an alternative method to obtain a more accurate temperature of the diode top contact without coating the sample with a high emissivity layer. [ABSTRACT FROM AUTHOR]

The paper reports on infra-red (IR) measurements made on silicon and gallium arsenide substrates which are transparent to IR radiation. The work showed that the measured emissivity is dependent on the wafer back-face technology, for example, a gold heat-sink or epoxy attachment. The work also indicated that the measured emissivity for the thermal mapping of a device is a function of the emitted radiation from the front, back face and layer interfaces, as well as internally reflected radiation and will be dependent on the thickness of the semiconductor wafer. Experimental work has shown that the two-temperature emissivity correction method will give a very accurate value of the total surface emissivity received from the sample. [ABSTRACT FROM AUTHOR]

The temperature and carrier density dependence of electron intrinsic saturation velocity (vsi) in a 0.3-μm gate length AlGaN/GaN HEMT was extracted from multibias S-parameter measurements. It was found that vsi fell rapidly with increasing sheet carrier concentration (ne), but was only a very weak function of ambient temperature (Tamb). This behavior is consistent with the hot-phonon model of carrier transport. [ABSTRACT FROM AUTHOR]

To accurately model distortion effects using a large signal model the variation of all the elements of the equivalent circuit model under bias conditions are required. A technique is presented to extract the source resistance Rs under bias conditions for the aluminium gallium nitride/gallium nitride (AlGaN/GaN) HEMT. The source resistance Rs is found to decrease as Vgs is increased, implying that the conduction channel becomes wider, which indicates a parallel conduction path to the 2D electron-gas. [ABSTRACT FROM AUTHOR]

To accurately model distortion effects using a large signal model the variation of all the elements of the equivalent circuit model under bias conditions are required. A technique is presented to extract the source resistance Rs under bias conditions for the aluminium gallium nitride/gallium nitride (AlGaN/GaN) HEMT. The source resistance Rs is found to decrease as Vgs is increased, implying that the conduction channel becomes wider, which indicates a parallel conduction path to the 2D electron-gas. [ABSTRACT FROM AUTHOR]