Fe delta-doped (In,Fe)Sb ferromagnetic semiconductor thin films for magnetic-field sensors with ultrahigh Hall sensitivity
Introduction
Ferromagnetic semiconductors (FMSs) belong to a family of materials with both properties of semiconductors and ferromagnets. In particular, transition metal (TM)-doped III-V FMSs have been intensively studied because of their compatibility with III-V electronic and photonic semiconductor devices. Recently, Fe-doped narrow-gap FMSs have generated great interest since it is possible to fabricate both p-type FMSs and n-type FMSs with Curie temperature (TC) higher than room temperature [1], [2], [3], [4]. Among them, n-type FMS (In,Fe)Sb is promising for device applications because its TC reaches room temperature at relatively low Fe concentration (16%) and it shows large anomalous Hall effect (AHE), which may be applied to magnetic-field sensors with ultrahigh Hall sensitivity [4]. It is well-known that in a FMS, the Hall resistivity, ρxy, is given by ρxy = RHH + RAHEM, where RH is the ordinary Hall coefficient, RAHE is the anomalous Hall coefficient, H is the external magnetic field, and M is the magnetization. Since RAHE >> RH, a FMS with relatively high TC and strong AHE may be used for magnetic-field sensors with ultrahigh sensitivity. While there are several studies of magnetic-field sensors using AHE [5], [6], [7], [8], [9], [10], the high sensitivities were observed only at low temperature or low magnetic field. In contrast, we show that (In,Fe)Sb can be used for the magnetic-field sensors with high Hall sensitivity at room temperature in the wider range of magnetic field.
In this study, to realize (In,Fe)Sb with ultrahigh Hall sensitivity, we have grown Fe δ-doped (In1−〈x〉,Fe〈x〉)Sb thin films with various average Fe concentrations (〈x〉 = 5–20%) and investigated their magnetic properties as well as AHE. The magnetic properties were characterized by magnetic circular dichroism (MCD) spectroscopy, which indicates intrinsic ferromagnetism in the Fe δ-doped (In,Fe)Sb thin films. From the MCD intensity vs. magnetic field characteristics, we estimated TC of Fe δ-doped (In,Fe)Sb thin films by Arrott plots. The TC of the Fe δ-doped (In1−〈x〉,Fe〈x〉)Sb tends to be lower than that of the Fe uniformly-doped (In1−x,Fex)Sb. However, the Fe δ-doped (In,Fe)Sb thin films show much larger AHE than the Fe uniformly-doped (In,Fe)Sb thin films, which is very promising for ultrahigh sensitive Hall sensors at room temperature.
Section snippets
Experiments and results
The schematic structure of our samples is shown in Fig. 1(a). The Fe δ-doped (In,Fe)Sb thin films were grown on semi-insulating GaAs (0 0 1) substrates by using low-temperature molecular beam epitaxy (LT-MBE) and the Fe δ-doping technique. First, we grew a 50-nm-thick GaAs buffer layer to obtain a smooth GaAs surface at 560 °C. Then, 10-nm-thick AlAs and 100-nm-thick AlSb buffer layers were grown at 560 °C and 480 °C, respectively, to relax the lattice mismatch between the GaAs layer and the
Summary
In summary, we have grown Fe δ-doped (In1−〈x〉,Fe〈x〉)Sb thin films with various average Fe concentrations (〈x〉 = 5–20%) by using LT-MBE and the Fe δ-doping technique. The magneto-optical properties characterized by MCD spectroscopy indicate the intrinsic ferromagnetism in the Fe δ-doped (In,Fe)Sb thin films. The TC of the Fe δ-doped (In1−〈x〉,Fe〈x〉)Sb tends to be lower than that of the Fe uniformly-doped (In1−x,Fex)Sb with the same x = 〈x〉. On the other hand, the Fe δ-doped (In,Fe)Sb thin films
Acknowledgment
This work is supported by Grants-in-aid for Scientific Research, CREST Program (No. JPMJCR1777) of Japan Science and Technology Agency, the Nanotechnology Platform 12025014 from MEXT, and Spintronics Research Network of Japan (Spin-RNJ).
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