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Applied Physics Letters, 2005
The circular photogalvanic effect (CPGE), induced by infrared radiation, has been observed in (00... more The circular photogalvanic effect (CPGE), induced by infrared radiation, has been observed in (0001)-oriented n − GaN quantum well (QW) structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spinsplitting 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. Gallium nitride is a potentially interesting material system for spintronics since it is expected to become ferromagnetic with a Curie-temperature above room temperature if doped with manganese [1]. Long spin relaxation times observed in this materials are another promising property for possible applications [2]. Little is known so far about spin orbit interaction in GaN based heterojunctions like existence of Rashba spin-splitting in the band structure which would provide a potential handle for spin manipulation [3]. Strong spin-orbit effects are expected to be in narrow-gap materials only [4]. A large piezoelectric effect which causes a strong electric field at the Al x Ga 1-x N/GaN interface and the strong polarization induced doping effect, on the other hand, may result in a sizeable Rashba contribution to spin-splitting of the band due to spin-orbit interaction (~ 1 meV) [5]. Indeed a spin-splitting of 9 meV was extracted from beatings of Shubnikov-de-Haas oscillations in Al 0.25 Ga 0.75 N/GaN heterostructures [6]. However, such beatings were ascribed to magneto-intersubband scattering by others [7]. On the other hand the observation of short spin relaxation times was attributed to D'yakonov Perel mechanism which requires Rashba spin splitting [8]. To investigate the presence of a sizeable spin-splitting in this material class we investigate the circular photogalvanic effect (CPGE) [9,10,11]. The CPGE as well as k-linear spin splitting of the band structure are only permitted in gyrotropic media. In such materials a linear relation between polar vectors (electric current j, quasi-momentum q etc.) and axial vectors (photon angular momentum, spin etc.) is allowed by symmetry. Both GaN/AlGaN QW structures and bulk GaN belong to the family of wurtzite-type semiconductors which are gyrotropic. As were pointed out in [12,13] in these media the spin-orbit part of the Hamiltonian has the form
Proceedings of the American Mathematical Society, 1963
Applied Physics Letters, 2005
The circular photogalvanic effect (CPGE), induced by infrared radiation, has been observed in (00... more The circular photogalvanic effect (CPGE), induced by infrared radiation, has been observed in (0001)-oriented n − GaN quantum well (QW) structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spinsplitting 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. Gallium nitride is a potentially interesting material system for spintronics since it is expected to become ferromagnetic with a Curie-temperature above room temperature if doped with manganese [1]. Long spin relaxation times observed in this materials are another promising property for possible applications [2]. Little is known so far about spin orbit interaction in GaN based heterojunctions like existence of Rashba spin-splitting in the band structure which would provide a potential handle for spin manipulation [3]. Strong spin-orbit effects are expected to be in narrow-gap materials only [4]. A large piezoelectric effect which causes a strong electric field at the Al x Ga 1-x N/GaN interface and the strong polarization induced doping effect, on the other hand, may result in a sizeable Rashba contribution to spin-splitting of the band due to spin-orbit interaction (~ 1 meV) [5]. Indeed a spin-splitting of 9 meV was extracted from beatings of Shubnikov-de-Haas oscillations in Al 0.25 Ga 0.75 N/GaN heterostructures [6]. However, such beatings were ascribed to magneto-intersubband scattering by others [7]. On the other hand the observation of short spin relaxation times was attributed to D'yakonov Perel mechanism which requires Rashba spin splitting [8]. To investigate the presence of a sizeable spin-splitting in this material class we investigate the circular photogalvanic effect (CPGE) [9,10,11]. The CPGE as well as k-linear spin splitting of the band structure are only permitted in gyrotropic media. In such materials a linear relation between polar vectors (electric current j, quasi-momentum q etc.) and axial vectors (photon angular momentum, spin etc.) is allowed by symmetry. Both GaN/AlGaN QW structures and bulk GaN belong to the family of wurtzite-type semiconductors which are gyrotropic. As were pointed out in [12,13] in these media the spin-orbit part of the Hamiltonian has the form
Proceedings of the American Mathematical Society, 1963