K. Hofbeck

High-frequency self-sustained current oscillation in an Esaki-Tsu superlattice monitored via microwave emission

Abstract We report the observation of a high-frequency self-sustained current oscillation in an n doped GaAs AlAs superlattice (at room temperature) that shows a negative differential conductance (Esaki-Tsu superlattice). The superlattice biased in the region of the negative differential conductance emitted microwave radiation at a fundamental frequency of about 6 GHz and at harmonics. We attribute the oscillation to space charge instabilities inside the superlattice caused by Bragg reflection of electrons in the lowest, wide miniband.

Self-sustained current oscillation above 100 GHz in a GaAs/AlAs superlattice

A GaAs/AlAs superlattice with a large miniband (120 meV) showed self-sustained current oscillation at a frequency of 103 GHz giving rise to microwave emission (power 0.5 mW). The emission line had a linewidth of about 1 MHz and was tuneable by about 800 MHz. An analysis suggests that the transport in the superlattice was mainly due to electrons in the lowest miniband and that the oscillation was caused by traveling dipole domains. We also observed frequency locking of the current oscillation attributed to a synchronization of domain propagation by the external high-frequency field.

Generation of millimeter waves with a GaAs/AlAs superlattice oscillator

We report on a semiconductor superlattice oscillator for generation of millimeter waves (frequency 65 GHz). The main element of the oscillator is a doped short-period GaAs/AlAs superlattice with negative differential conductance. The oscillator is due to current oscillations caused by charge density domains. The oscillator delivered, at an efficiency of 0.2% for the conversion of electrical power to radiation power, a power of 100 μW in a bandwidth of the order of 200 kHz.

Millimeter wave oscillator based on a quasiplanar superlattice electronic device

We report on a millimeter wave oscillator based on a quasiplanar superlattice electronic device (SLED). The SLED, a lateral structured GaAs/AlAs superlattice, showing, at room temperature, a negative differential conductance, was provided with two terminals lying in one plane and mounted in a waveguide structure. The oscillator delivered radiation, in a relative bandwidth of 10−5, that was tunable by about 10% around 70 GHz and had a power of 100 μW; depending on the voltage across the superlattice, additional oscillation lines (up to 180 GHz) appeared. We associate the generation of radiation with a current oscillation caused by traveling dipole domains in the superlattice.

Millimeter wave generation by a self-sustained current oscillation in an InGaAs/InAlAs superlattice

We report millimeter wave generation by a self-sustained current oscillation in a doped InGaAs/InAlAS wide miniband superlattice. The superlattice (miniband width 160 meV) showed, at room temperature, a current voltage characteristic with negative differential conductance. Coupled to a high-frequency circuit, the superlattice generated millimeter waves, at a frequency (55 GHz) which was tunable by half a percent by changing the bias voltage. The power (0.3 mW) corresponded to an efficiency (i.e., ratio of microwave power to dc power input) of 0.3%. We attribute the microwave generation to a current oscillation caused by traveling dipole domains.

Superlattice frequency multiplier for generation of submillimeter waves

We observed frequency multiplication of 65-GHz radiation up to the fifth harmonic (325 GHz; wavelength 0.9 mm) in a superlattice with negative differential conductance at room temperature. The efficiency of multiplication depended strongly on both the strength of a static field and the strength of the 65-GHz field. An analysis of the results shows that the nonlinear current, responsible for the frequency multiplication, was governed by the Esaki-Tsu current-voltage characteristic that describes the transport of carriers in large-miniband superlattices.

Frequency-locked GaAs/AlAs superlattice oscillator for tunable narrowband microwave generation

We observed frequency locking of a wide-miniband GaAs/AlAs superlattice oscillator. The oscillator showed a free self-sustained current oscillation giving rise to microwave generation (power 100 μW) at a natural frequency (near 5 GHz) and ultraharmonics. A narrowband driving field locked the oscillator and caused a drastic narrowing (from 106 Hz to less than 10 Hz) of the halfwidths of the microwave lines, now centered at the driving frequency and its harmonics; at a driving power of 10 μW we obtained a locking range of 1% around the natural frequency. Our experiment, performed with a superlattice integrated in a planar microwave circuit, shows that a locked superlattice oscillator is suitable for tunable narrowband generation of high-frequency radiation.

Tunable narrowband microwave radiation source based on a frequency-locked superlattice oscillator

We report on the generation of tunable ultra-narrowband microwave radiation using a frequency locked superlattice oscillator fabricated in a planar design. As active device, a wide-miniband GaAs/AlAs superlattice was used, showing, at room temperature, self-sustained current oscillation giving rise to microwave generation at a natural frequency near 5 GHz and ultraharmonics up to the 7th order; the linewidth of the harmonics was near 1 MHz. We observed a drastic reduction of the linewidths to less than 10 Hz by frequency locking the oscillator (approximately 100 (mu) W) with a weak narrowband driving field (approximately 0.1 (mu) W). The oscillator was tunable within a locking range of 1 percent of the natural frequency. Besides harmonic also subharmonic locking was observed.

Narrowband microwave emission by a frequency-locked current oscillation in a GaAs/AlAs superlattice

We report on frequency locking of a self-sustained current oscillation in a GaAs/AlAs wide miniband superlattice oscillator emitting microwave radiation at 23 GHz with a power of about 0.3 mW. The current oscillation was caused by travelling dipole domains and the locking was due to interaction of the domains with an external narrowband high-frequency field. We observed that the linewidth of the frequency-locked oscillation was less than 10 Hz compared to 105 Hz for the free oscillator, indicating synchronisation of the dipole domain propagation with the external field.