Magnetically Controlled Photovoltaic Diode Structure

We propose a new integrated device for spintronics application, which is based on a hybrid metal-semiconductor structure. The device consists of a Si-based p-i-n photodetector sandwiched between two layers of a ferromagnetic metal (3d ferromagnet or half-metallic compound). The photocurrent flowing in such a system is shown to depend on its magnetic configuration. This, in turn, allows controlling the device performance by an externally applied magnetic field. We have estimated magnitude of the effect and also determined the role of relevant material parameters. INTRODUCTION Recently, many efforts have been undertaken to integrate semiconductors and magnetic metals into magnetoelectronic devices [1]. The main idea is to make use of spin-polarized electrons injected from a magnetic metal into a nonmagnetic semiconductor. If realized, this would enable to design new devices, like for instance magnetically controlled transistors, or others. Unfortunately, the efficiency of spin injection across the junction between a magnetic metal and a nonmagnetic semiconductor turns out to be small because of a large difference in electrical resistivity [2]. From this point of view, the use of ferromagnetic semiconductors instead of metals might resolve the problem. However, the best known ferromagnetic semiconductor, GaMnAs, has critical temperature about 110 K [3], which is too small for most applications. Therefore, hybrid structures like metal-semiconductor junctions are of great interest. It was shown that the metal-semiconductor incompatibility can be overcome by introducing tunneling barriers at the interface, which can effectively decrease the spin relaxation [4, 5]. In this paper we propose a new magnetically controlled photodetector, that consists of the semiconductor p-i-n structure and two thin films of a magnetic metal. The device does not suffer from the metal-semiconductor incompatibility. Magnetic sensitivity of the photoresponse current is of the same physical origin as the giant magnetoresistance (GMR) effect in metallic magnetic multilayers [6-9]. Therefore, this magnetic sensitivity will be referred to in the following as the GMR effect, too. Our estimations and theoretical calculations show that the GMR effect under illumination is much larger than that in equilibrium conditions. The enhancement of GMR is attributed to the illumination induced spin-polarized electron-hole pairs. Mat. Res. Soc. Symp. Proc. Vol. 721 © 2002 Materials Research Society