Inverse Bloch-oscillator: Strong Thz-photocurrent resonances at the Bloch frequency
- Univ. of California, Santa Barbara, CA (United States); and others
We have observed resonant changes in the current-voltage characteristics of miniband semiconductor superlattices when the Bloch frequency is resonant with a terahertz field and its harmonics: the inverse Bloch oscillator effect. The resonant feature consists of a peak in the current which grows with increasing laser intensity accompanied by a decrease of the current at the low bias side. The peak position moves linearly with the laser frequency. When the intensity is increased further the first peak starts to decrease and a second peak at about twice the voltage of the first peak is observed due to a two photon resonance. At the highest intensities we observe up to a four photon resonance. A superlattice is expected to show negative differential conductance due to the strong nonparabolicity of the miniband. In this situation the carriers should undergo Bloch oscillations with a frequency {omega}{sub B} = eEd/h. Transient Bloch oscillations of photo excited carriers have been observed in time resolved Thz emission measurements. However, the possibility of Thz generation form a DC voltage biased superlattice is still under discussion. We have approached this problem by exploring the inverse Bloch oscillator effect in a superlattice excited by the Thz radiation form the UCSB FEL. The superlattice consists of 40 periods of 80{angstrom} GaAs wells and 20{angstrom} Al{sub 0.3}Ga{sub 0.7}As barriers. To couple the electric field of the Terahertz radiation parallel to the growth direction a coplanar bowtie antenna has been employed. Our results show clearly that the external radiation couples to Bloch oscillations in contrary to theoretical suggestions that Thz radiation would not couple to a uniform Wannier Stark ladder. We conclude that this result is intimately related to dissipation and line broadening of the otherwise identical states in the ladder: absorption appears above the Wannier Stark splitting ({omega}{sub B}<{omega}) and gain below ({omega}{sub B}>{omega}).
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- OSTI ID:
- 238901
- Report Number(s):
- BNL-61982-Absts.; CONF-9508156-Absts.; ON: DE96002729; TRN: 96:013395
- Resource Relation:
- Journal Volume: 76; Journal Issue: 16; Conference: 17. international free electron laser conference, New York, NY (United States), 21-25 Aug 1995; Other Information: PBD: [1995]; Related Information: Is Part Of 17th international free electron laser conference and 2nd international FEL users` workshop. Program and abstracts; PB: 300 p.
- Country of Publication:
- United States
- Language:
- English
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