We report on the resonant, voltage tunable emission of terahertz radiation ͑0.4 -1.0 THz͒ from a gated two-dimensional electron gas in a 60 nm InGaAs high electron mobility transistor. The emission is interpreted as resulting from a current driven plasma instability leading to oscillations in the transistor channel ͑Dyakonov-Shur instability͒.Plasma waves in a gated two-dimensional electron gas have a linear dispersion law, similar to that of sound waves. The transistor channel acts as a resonator cavity for plasma waves that can reach THz frequencies for a sufficiently short ͑nanometer-sized͒ field effect transistor. 1 As was predicted in Ref. 2, when a current flows through a field effect transistor, the steady state can become unstable against the generation of plasma waves ͑Dyakonov-Shur instability͒ leading to the emission of an electromagnetic radiation at plasma wave frequencies. The emission is predicted to have thresholdlike behavior. It is expected to appear abruptly after the device current exceeds a certain threshold value for which the increment of the plasma wave amplitude exceeds losses related to electron collisions with impurities and/or lattice vibrations.The excitation of plasma waves in a field effect transistor channel can be also used for the detection of terahertz radiation. 3 Recent reports demonstrated a resonant 4 detection in GaAs-based high electron mobility transistors ͑HEMTs͒ and in gated double quantum well heterostructures. 5 This is the first report of resonant THz emission by plasma generation. The terahertz emission ͑0.4 -1.0 THz͒ was obtained by using an InGaAs HEMT with a 60-nm-long gate. We show that the results can be interpreted assuming that the emission is caused by the current driven plasma instability leading to terahertz oscillations in the channel through Dyakonov-Shur instability.Lattice-matched InGaAs/AlInAs HEMTs grown by molecular beam epitaxy on an InP substrate were used in this study. The active layers consisted of a 200 nm In 0.52 Al 0.48 As buffer, a 20 nm In 0.53 Ga 0.47 As channel, a 5-nm-thick undoped In 0.52 Al 0.48 As spacer, a silicon planar doping layer of 5ϫ10 12 cm Ϫ2 , a 12-nm-thick In 0.52 Al 0.48 As barrier layer, and, finally, a 10-nm-silicon-doped In 0.53 Ga 0.47 As cap layer. Details of the technological process are given elsewhere. 6 The gate length was 60 nm, and the drain-source separation was 1.3 m. An InP-based HEMT was chosen for its high InGaAs channel mobility and high sheet carrier density.Output and transfer characteristics are shown in Fig. 1. The low field, linear output region is marked by the dotted line. The deviation of the I d (U sd ) curve from linear behavior indicates the beginning of the saturation region. The arrow indicates the emission threshold voltage, U sd ϳ200 mV at I d ϳ4.5 mA. The horizontal dashed line shows the level of the current saturation (I d ϳ4.8 mA). The I d (U sd ) characteristic shows an unstable behavior for U sd higher than 300 mV. This well-known phenomenon is related to a self-excitation a͒ Also at

By using a Monte Carlo simulator, the static and dynamic characteristics of 50-nm-gate AlInAs-GaInAs-doped high-electron mobility transistors (HEMTs) are investigated. The Monte Carlo model includes some important effects that are indispensable when trying to reproduce the real behavior of the devices, such as degeneracy, presence of surface charges, T-shape of the gate, presence of dielectrics, and contact resistances. Among the large quantity of design parameters that enter the fabrication of the devices, we have studied the influence on their performance of two important factors: the doping level of the-doped layer, and the width of the devices. We have confirmed that the value of the-doping must be increased to avoid the reduction of the drain current due to the depletion of the channel by the surface potential. However, a higher-doping has the drawback that the frequency performance of the HEMTs is deteriorated, and its value must be carefully chosen depending on the system requirements in terms of delivered power and frequency of operation. The reduction of the device width has been also checked to improve the cutoff frequencies of the HEMTs, with a lower limit imposed by the degradation provoked by the offset extrinsic capacitances.

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