E. Schomburg

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.

THz-field induced nonlinear transport and dc voltage generation in a semiconductor superlattice due to Bloch oscillations

We report on a theoretical analysis of terahertz (THz-) field induced nonlinear dynamics of electrons in a semiconductor superlattice that are capable to perform Bloch oscillations. Our results suggest that for a strong THz-field a dc voltage should be generated. We have analyzed the real-time dynamics using a balance equation approach to describe the electron transport in a superlattice miniband. Taking account of both Bloch oscillations of electrons in a superlattice miniband and dissipation, we studied the influence of a strong THz-field on currently available superlattices at room temperature. We found that a THz-field can lead to a negative conductance resulting in turn in a THz-field induced dc voltage, and that the voltage per superlattice period should show, for varying amplitue of the THz-field, a form of wisted plateaus with the middle points being with high precision equal to the photon energy divided by the electron charge. We show voltage to the finite voltage state, and that in the finite voltage state dynamic localization of the electrons in a miniband occurs.

Frequency doubling and tripling of terahertz radiation in a GaAs/AlAs superlattice due to frequency modulation of Bloch oscillations

We report on frequency doubling and tripling of THz radiation in a voltage-biased GaAs/AlAs superlattice. By use of a corner cube antenna system, radiation from the Santa Barbara free-electron laser (frequency 0.7 THz) was guided into a superlattice mesa element and the second and third harmonic were coupled out of the mesa. Without bias only radiation of the third harmonic was generated, while the biased superlattice emitted radiation of both the second and third harmonic. We attribute the harmonic generation to frequency modulation of damped Bloch oscillations of the miniband electrons in the superlattice.

Ultrafast detection and autocorrelation of picosecond THz radiation pulses with a GaAs/AlAs superlattice

We used a wide miniband GaAs/AlAs superlattice (at room temperature) for detection and autocorrelation of picosecond THz radiation pulses (frequency 4.3 THz) from a free-electron laser. The detection was based on a THz-field induced change in conductivity of the superlattice, and the correlation on the nonlinearity of the conductivity change at strong THz-pulse-power. The nonlinear conductivity change was due to two effects, which we attribute to dynamical localization of miniband electrons and to ionization of deep impurity centers.

Feasibility of a semiconductor superlattice oscillator based on quenched domains for the generation of submillimeter waves

We discuss the feasibility of a semiconductor superlattice oscillator which exploits the quenching of propagating dipole domains for the generation of submillimeter waves. We studied the dynamics of electrons in a semiconductor superlattice by performing a simulation based on a drift-diffusion model, taking into account feedback from a resonant circuit. The simulation delivers propagating dipole domains which are quenched before they reach the anode. The periodic formation and quenching of domains creates a self-sustained oscillation of the current through the superlattice. The frequency of the oscillation can be more than three times higher than without feedback. We suggest that with already existing superlattices an oscillator working in the quenched domain mode can be realized up to almost 500 GHz.

Suppression of current through an Esaki–Tsu GaAs/AlAs superlattice by millimeter wave irradiation

We report the observation of suppression of the dc current through an Esaki–Tsu GaAs/AlAs superlattice (that shows a negative differential conductance due to Bloch oscillations of miniband electrons) caused by irradiation with millimeter wave radiation (frequency 78 GHz). A theoretical analysis of the dc current indicated that the high‐frequency electric current followed the high‐frequency field with a response time smaller than the period (∼10−11 s) of the field. Our experiment, with the superlattice at room temperature, demonstrates that the Esaki–Tsu superlattice is suitable for ultrafast millimeter wave detection and other high‐frequency applications.

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.

Detection of THz radiation with semiconductor superlattices at polar-optic phonon frequencies

The nonlinear response of GaAs/AlAs superlattices to THz radiation has been analyzed over a wide frequency range (0.1 THz–15 THz), including the range of polar-optic phonon frequencies. Assuming that free electrons in a superlattice subjected to both a static and a THz field perform frequency-modulated damped Bloch oscillations, we have calculated a superlattice current responsivity, i.e., the ratio of the direct current change to the power of the incident radiation. The responsivity of superlattices has been measured in several recent experiments. An equivalent circuit taking into account the resonant properties associated with polar-optic phonons was used in a self-consistent treatment of the problem. It is shown that the responsivity is suppressed at frequencies of infrared-active, transverse polar-optic phonons due to dynamic screening of the THz field by the lattice. In contrast, the responsivity strongly increases at longitudinal polar-optic phonon frequencies due to a large enhancement of the THz f...