Wolfgang Weber

Demonstration of Rashba spin splitting in GaN-based heterostructures

The circular photogalvanic effect, induced by infrared radiation, has been observed in (0001)-oriented n‐GaN low dimensional structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spin splitting of the conduction band in k space in this type of materials. The observation suggests the presence of a sizeable Rashba type of spin splitting, caused by the built-in asymmetry at the AlGaN∕GaN interface.

Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures

Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.

Magneto-gyrotropic photogalvanic effects in semiconductor quantum wells

We show that free-carrier (Drude) absorption of both polarized and unpolarized terahertz radiation in quantum well (QW) structures causes an electric photocurrent in the presence of an in-plane magnetic field. Experimental and theoretical analysis evidences that the observed photocurrents are spin dependent and related to the gyrotropy of the QWs. Microscopic models for the photogalvanic effects in QWs based on asymmetry of photoexcitation and relaxation processes are proposed. In most of the investigated structures the observed magneto-induced photocurrents are caused by spin-dependent relaxation of non-equilibrium carriers.

Subnanosecond Ellipticity Detector for Laser Radiation

A room temperature detector of terahertz laser radiation ellipticity has been developed based on the simultaneous measurements of three different photoelectric phenomena: circular photogalvanic effect, linear photogalvanic effect, and photon drag effect. Each of these effects, which have subnanosecond time constants, is monitored by different detector units stacked together in one detector.

All-electric detection of the polarization state of terahertz laser radiation

Two types of room-temperature detectors of terahertz laser radiation have been developed which allow, in an all-electric manner, the determination of the plane of polarization of linearly polarized radiation and the Stokes parameters of elliptically polarized radiation, respectively. The operation of the detectors is based on photogalvanic effects in semiconductor quantum well structures of low symmetry. The photogalvanic effects have nanosecond time constants at room temperature, making a high time resolution of the polarization detectors possible.

Magneto-gyrotropic photogalvanic effects in GaN/AlGaN two-dimensional systems

Magneto-gyrotropic photogalvanic and spin-galvanic effects are observed in (0001)-oriented GaN/AlGaN heterojunctions excited by terahertz radiation. We show that free-carrier absorption of linearly or circularly polarized terahertz radiation in low-dimensional structures causes an electric photocurrent in the presence of an in-plane magnetic field. Microscopic mechanisms of these photocurrents based on spin-related phenomena are discussed. Properties of the magneto-gyrotropic and spin-galvanic effects specific for hexagonal heterostructures are analyzed.

Picosecond Polarisation Detector for Infrared and Terahertz Radiation

We report on a room temperature detector of infrared/terahertz laser radiation allowing to measure and characterized the radiation polarization state with picosecond time resolution.

Subnanosecond polarisation detector for infrared and terahertz radiation

We report on a room temperature detector of infrared/THz laser radiation allowing to measure the radiation polarization state with picosecond time resolution. The ellipticity of radiation is analyzed applying three photoelectric phenomena: circular photogalvanic effect, linear photogalvanic effect, and photon drag effect. Each of these effects is monitored by different detector units stacked together in one detector.

Demonstration Of Rashba Spin Splitting In GaN‐based Heterostructures

The circular photogalvanic effect (CPGE), induced by infrared radiation, has been observed in (0001)‐oriented GaN low dimensional structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spin splitting of the conduction band in k‐space in this type of materials. The observation suggests the presence of a sizeable Rashba type of spin splitting, caused by the built‐in asymmetry at the AlGaN/GaN interface.

Rashba Spin-Splitting and Spin Currents in GaN Heterojunctions

The circular photogalvanic effect, spin-galvanic effect and magneto-gyrotropic effect have been observed in hexagonal (0001)-oriented GaN low-dimensional structures excited by infrared and terahertz radiation. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the gyrotropy of the GaN based heterojunctions and give evidence for a substantial structural inversion asymmetry caused by the built-in electric fields at the AlGaN/GaN interface.