Atsushi Teranishi

Fundamental oscillation of resonant tunneling diodes above 1 THz at room temperature

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.

Fundamental Oscillation of up to 831 GHz in GaInAs/AlAs Resonant Tunneling Diode

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 optimized (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.

Frequency Increase of Resonant Tunneling Diode Oscillators in Sub-THz and THz Range Using Thick Spacer Layers

We obtained frequency increase of resonant tunneling diode (RTD) oscillators using thick spacer layers at the collector in sub-terahertz range. This is attributed to reduction of parasitic capacitance due to the increase of spacer layer thickness. The oscillation frequency increased from 325 to 425 GHz by the change of spacer layer thickness from 5 to 45 nm in reasonable agreement with theoretical calculation. Frequency switching with bias direction was also obtained for an RTD having an asymmetric structure with the thickness of the collector and emitter spacer layers of 30 and 5 nm, respectively. The oscillation frequency was 394 GHz under forward bias, whereas 336 GHz under reverse bias in which the role of the emitter and collector spacers was exchanged.

Extremely High Peak Current Densities of over 1×106 A/cm2 in InP-Based InGaAs/AlAs Resonant Tunneling Diodes Grown by Metal–Organic Vapor-Phase Epitaxy

InP-based InGaAs/AlAs resonant tunneling diodes (RTDs) with extremely high peak current density ( jP) were grown by metal–organic vapor-phase epitaxy. High-temperature growth at 660 °C provides high-quality heterointerfaces and excellent current–voltage (I–V) characteristics. To obtain extremely high jP, the structural parameter dependence of I–V characteristics on barrier and spacer thicknesses and emitter-doping concentration were examined. Clear exponential dependence of jP on barrier thickness was obtained in the barrier-thickness range from 1.2 to 2.8 nm. The reduction of spacer thickness to 2 nm increased jP without deteriorating the peak-to-valley current ratio (PVR). An investigation of Si dopant diffusion into double-barrier regions at the growth temperature supports the validity of reducing spacer thickness. The jP increased as Si doping concentration was increased from 1×1018 to 6×1018 cm-3 in InGaAs emitters. The highest jP reached 1.29×106 A/cm2 with a PVR of 1.5 in a RTD at room temperature with barrier and spacer thicknesses of 1.4 and 2 nm and Si doping concentration in the emitter of 6×1018 cm-3.

Fundamental Oscillation of up to 915 GHz in Small-Area InGaAs/AlAs Resonant Tunneling Diodes with Planar Slot Antennas

A fundamental oscillation of up to 915 GHz was observed at room temperature in small-area InGaAs/AlAs resonant tunneling diodes (RTDs) with planar slot antennas. The dependence of the oscillation frequency on the RTD mesa area was also shown. Although the output power was small (a few tens of nanowatts) in this study owing to the relatively low available current density (difference in current density between the peak and the valley: ~3 mA/µm2) and the small mesa area (~0.63 µm2), it was expected that the output power can be increased by a high available current density.

Fundamental oscillation up to 1.08THz in resonant tunneling diodes with high-indium-composition transit layers for reduction of transit delay

Fundamental oscillations up to 1.08THz with the output power of 5.5 microwatts was achieved in GaInAs/AlAs resonant tunneling diodes (RTDs) at room temperature. The graded emitter, thin barriers, and high-indium-composition transit layers were introduced to reduce the tunneling and transit delays. The first two of these structures are the same as those in RTDs oscillating at 1.04THz reported recently, and the last structure provided for further reduction of the transit time and increase in frequency due to suppression of the Γ-L transition and increment of the launching velocity.

Structural and electrical transport properties of MOVPE-grown pseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes on InP substrates

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 (JP) 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.

Fundamental oscillation up TO 831 GHz in GaInAs/AlAs resonant tunneling diode

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 optimized (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.

Resonant Tunneling Diodes with Very High Peak Current Density Using Thin Barrier and High Emitter Doping

We obtained InGaAs/AlAs double-barrier resonant tunneling diodes (DB RTDs) with very high peak current density using thin barrier and high emitter doping. The peak current density of 13 mA/mum2 with the peak/valley current ratio of 1.5 was obtained for 1.4-nm-thick barrier and emitter doping concentration of 6 times 1018cm-3. By these characteristics, oscillators with the fundamental oscillation exceeding 1 THz are sufficiently possible.

Fundamental oscillation up to 915GHz in InGaAs/AlAs resonant tunneling diodes integrated with slot antennas

A fundamental oscillation up to 915GHz was observed at room temperature in InGaAs/AlAs resonant tunneling diode integrated with planar slot antennas. By reducing the mesa area, parasitic capacitance of resonant tunneling diode was decreased. The output power was small (around a few tens nW) at present because of a small area (≈0.63μm2) and a low available current density (≈3mA/μm2) which is the difference in current density between the peak and valley. The dependence of fundamental oscillation frequency on mesa area is also shown.