Computer Physics Communications ( ) – Contents lists available at SciVerse ScienceDirect Computer Physics Communications journal homepage: www.elsevier.com/locate/cpc Simulation of the spin polarization and the charge transport in Zener tunnel junctions based on ferromagnetic GaAs and ZnO E. Comesaña a,∗ , M. Aldegunde b , A.J. Garcia-Loureiro a a Departamento de Electrónica e Computación, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain b College of Engineering, Swansea University, Swansea SA2 8PP, United Kingdom article info Article history: Received 16 May 2012 Received in revised form 16 November 2012 Accepted 20 November 2012 Available online xxxx Keywords: Magnetoelectronics Spintronics Spin-polarized transport in semiconductors Junction diodes Tunneling III–V semiconductors II–VI semiconductors abstract Simulations of the tunneling current as a function of voltage for a Zener diode where both sides are ferromagnetic have been performed. The current is evaluated as a function of the voltage and of the magnetization on each side of the diode. Calculations are made using an in-house developed simulator which solves the Poisson, electron and hole continuity equations self-consistently. The drift-diffusion model is used to calculate the charge carrier distribution. The current expressions were modified to consider degenerate semiconductors. Our simulator includes a non-local tunneling transport model which was modified to account for the spin polarization of the carriers. The tunneling magnetoresistance is obtained from the I–V characteristics for parallel and antiparallel configurations of the magnetization vectors in each side of the device. Two different devices were analyzed, one that corresponds to Mn- doped GaAs in which the ferromagnetism is stronger on the p side of the diode, and the other that corresponds to ZnO where there are likely to be many more carriers on the n side of the diode. We found good agreement between the results of our simulations and the theoretical predictions of the tunneling magnetoresistance, especially at room temperature. We also found that larger bandgap materials show larger tunneling current but lower tunnel magnetoresistance. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Diluted magnetic semiconductors (DMSs) are considered to be new-generation materials with the most potential for the future developing of new spintronic technologies and new spin-based device applications. DMSs provide simultaneous control on the flow of the carrier charge and spin [1]. Spintronics is motivated by the belief that spin-signal processing may yield advantages in terms of processing speed, power consumption or device density. Since the prediction of high Curie temperature DMSs, based on III–V semiconductors [2], the search for such materials has re- ceived much attention as they are keystones for the developing of spintronics. In an optimally doped DMS the density of carriers is approximately half of the density of magnetic ions, which is usu- ally between x = 5% and x = 15% (x is the fraction of magnetic ions added to the semiconductor). The well-established DMSs oc- cur with one type of carrier. One of the most investigated materials is the III–V material (Ga 1−x Mn x )As, in which the Mn ion provides a localized spin S = 5/2 and also contributes a hole [3]. The holes are degenerate and strongly polarized at low temperatures [4]. De- spite the fact that non-ferromagnetic GaAs is easy to dope to both p type and n type, the ferromagnetic III–V-doped materials are all ∗ Corresponding author. E-mail address: enrique.comesana@usc.es (E. Comesaña). p type. However, there is much effort being made to find a compati- ble n-type ferromagnetic semiconductor [5,6]. Magnetic properties have been seen also in a number of magnetically doped oxides, par- ticularly ZnO, TiO 2 and SnO 2 [7–9], all of which occur as n-type semiconductors. Even though there is experimental evidence of p-type ZnO, it is extremely difficult to dope and the samples show very low conductivity and still they are not in the Zener regime [10,11]. There is growing interest in the developing of magnetic tunnel junctions based on (Zn 1−x Co x )O with different barriers [12,13] because of its high Curie temperature and promising mag- netotransport [14–16]. A pn junction of two highly degenerated semiconductors makes a tunneling diode which has many applications [17], and adding magnetic functionality would enable more devices such as mag- netic switching of microwave devices. Zener tunneling has been observed in a ferromagnetic/non-magnetic (GaMn)As/GaAs het- erostructure [18] and a high spin polarization is observed opti- cally [19]. The voltage dependence of the tunneling current in a spin-polarized Zener diode, as shown in Fig. 1, is well fitted by the theory of a non-magnetic diode [4]. We are developing analyti- cal [20] and numerical models [21] to study the transport in ferro- magnetic Zener diodes. Using these models we have predicted the dependence of the tunneling current on the mean magnetization of the system and we have evaluated the tunneling magnetoresis- tance (TMR) in a theoretical both-sided-ferromagnetic diode with different spin-polarization ratios. 0010-4655/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cpc.2012.11.010