Fundamental oscillations up to 1.04 THz were achieved in resonant tunneling diodes at room temperature. A graded emitter and thin barriers were introduced in GaInAs/AlAs double-barrier resonant tunneling diodes for reductions of the transit time in the collector depletion region and the resonant tunneling time, respectively. Output powers were 7 μW at 1.04 THz and around 10 μW in 0.9–1 THz region. A change in oscillation frequency of about 4% with bias voltage was also obtained.

A fundamental oscillation of up to 831 GHz was observed at room temperature in GaInAs/AlAs resonant tunneling diodes integrated with planar slot antennas. The thickness of the collector spacer layer was increased (20 nm) and the mesa area (<1 µm2) was reduced in order to reduce the resonant tunneling diode capacitance. Reduction in the negative differential conductance in the small mesa area was prevented by increasing the emitter doping concentration (3×1018 cm-3) which resulted in an ultra-high peak current density (18 mA/µm2) with a peak-to-valley current ratio of 2. The dependence of oscillation frequency on the mesa area was also studied. The output power was at least 1 µW.

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We report resonant tunneling diode (RTD) oscillators with a high output power of around 400 µW at frequencies of 530–590 GHz. RTDs with a graded emitter and thin barriers were employed to obtain large negative differential conductance at high frequencies for high output power. An optimized structure of offset slot antennas was also used to maximize the radiation conductance. The highest output power obtained in this study was 420 µW at 548 GHz for an RTD with a peak current density of 24 mA/µm2; the RTD was placed 58 µm apart from the center of a 130-µm-long slot antenna.

We demonstrate the operation of resonant tunneling diode (RTD) oscillators with high output power (100–200 µW) at frequencies of 430–460 GHz using an offset-fed slot antenna in which the RTD is placed at a certain distance from the center of the slot. The highest output power obtained in this study was 200 µW at 443 GHz for a single RTD with a peak current density of 18 mA/µm2; the RTD was placed 45 µm from the center of a 100-µm-long antenna. Higher output is expected by optimizing the position and mesa area of the RTD and the antenna length.

We report metal–organic vapor-phase epitaxy (MOVPE) growth of pseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes (RTDs) on InP substrates for the first time. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations reveal that a uniform strained InAs subwell is coherently grown in the double-barrier (DB) structure. The AlAs/InGaAs/InAs RTDs exhibit excellent current–voltage characteristics with a high peak current density (J P) of around 2 × 105 A/cm2 and peak-to-valley ratio (PVR) of around 6. A comparison with control RTDs consisting of AlAs/In0.8Ga0.2As DB confirms the effectiveness of InAs subwell insertion for the improvement of PVR.

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