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We report on room temperature terahertz generation by a submicron size AlGaN/GaN-based high electron mobility transistors. The emission peak is found to be tunable by the gate voltage between 0.75 and 2.1 THz. Radiation frequencies correspond to the lowest fundamental plasma mode in the gated region of the transistor channel. Emission appears at a certain drain bias in a thresholdlike manner. Observed emission is interpreted as a result of Dyakonov–Shur plasma wave instability in the gated two-dimensional electron gas. [ABSTRACT FROM AUTHOR]

Microwave frequency capabilities of AlGaN/GaN high electron mobility transistors (HEMTs) on high resistive silicon (111) substrate for power applications are demonstrated in this letter. A maximum dc current density of 1 A/mm and an extrinsic current gain cutoff frequency (FT) of 50 GHz are achieved for a 0.25 μm gate length device. Pulsed and large signal measurements show the good quality of the epilayer and the device processing. The trapping phenomena are minimized and consequently an output power density of 5.1 W/mm is reached at 18 GHz on a 2 ⊗ 50 ⊗ 0.25/μm² HEMT with a power gain of 9.1 dB. [ABSTRACT FROM AUTHOR]

The hot-electron transfer ratio from the Schottky emitter diode to the Schottky collector diode through the thin base layer of Si-CoSi2-Si metal base transistors has been measured in devices for which the pinhole contribution to the current gain is shown by transconductance measurements to be negligible. The common-base current gain α of the transistors, measured as a function of temperature and base thickness, exhibits an exponential dependence on CoSi2 film thickness, from which a ballistic mean free path is deduced. This value is in good agreement with the mean free path deduced from conductivity data, both at 77 and 300 K. The behavior of the pre-exponential coefficient, i.e., the gain extrapolated to zero base thickness, is not completely understood and shows evidence for hot-electron and space-charge effects in the epitaxial overgrown Si material of the emitter. [ABSTRACT FROM AUTHOR]

The first results obtained from AlGaN/GaN HEMT devices on MBE epitaxial structures grown on ‘composite’ substrates are presented. These substrates are based on innovative structures in which a thin Si single crystal layer is transferred on top of a thick polycrystalline SiC wafer. The fabrication of the transistors is based on a process flow close to those used on epitaxy on Si bulk substrates. The results show the capabilities of such composite devices, providing HEMT devices for microwave power applications. [ABSTRACT FROM AUTHOR]

The reliability of Mo-based Schottky contact for an AlGaN/GaN HEMT after a thermal storage test is reported. Electrical and chemical analyses demonstrate the stability of Mo/Au gate for a GaN HEMT after a 2000 h ageing test at temperatures up to 340°C. [ABSTRACT FROM AUTHOR]

Abstract: The excessive gate leakage current of the planar- and mesa-type InAlN/GaN heterostructure field-effect transistors (HFETs) is evaluated. It is found that the gate current of the mesa-type HFETs is higher than that of the planar devices, particularly at low biases. Analyses of the gate current considering different transport mechanisms yielded identical thermionic currents (i.e., an identical Schottky barrier height) but a significantly higher leakage component in the mesa-type HFETs than in the planar devices. This additional current component observed in the mesa-type devices shows a nearly ohmic behavior. Mapping by the electron-beam induced current technique confirms an enhanced current located under the expanded gate contact and on the part of the mesa-sidewall, where the gate contact is placed. Two-dimensional simulation of the device structure shows that considerable part of the gate leakage current flows through the GaN buffer layer. These results underline the importance of a proper design of the device structure and layout (i.e., the use of planar structure with device insulation prepared by ion implantation rather than by mesa technique), and of the preparation of the GaN buffer (it should be semi-insulating) in order to fabricate reliable, low leakage current GaN-based HFETs. [Copyright &y& Elsevier]

Abstract: We report on preparation and electrical characterization of InAlN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors (MOS HEMTs) with Al2O3 gate insulation and surface passivation. About 12nm thin high-κ dielectric film was deposited by MOCVD. Before and after the dielectric deposition, the samples were treated by different processing steps. We monitored and analyzed the steps by sequential device testing. It was found that both intentional (ex situ) and unintentional (in situ before Al2O3 growth) InAlN surface oxidation increases the channel sheet resistance and causes a current collapse. Post deposition annealing decreases the sheet resistance of the MOS HEMT devices and effectively suppresses the current collapse. Transistors dimensions were source-to-drain distance 8μm and gate width 2μm. A maximum transconductance of 110mS/mm, a drain current of ∼0.6A/mm (VGS =1V) and a gate leakage current reduction from 4 to 6 orders of magnitude compared to Schottky barrier (SB) HEMTs was achieved for MOS HEMT with 1h annealing at 700°C in forming gas ambient. Moreover, InAlN/GaN MOS HEMTs with deposited Al2O3 dielectric film were found highly thermally stable by resisting 5h 700°C annealing. [Copyright &y& Elsevier]