Tuning ferromagnetic semiconductors by ion irradiation

Ion irradiation has been widely used to render a semiconductor layer highly resistive through the creation of carrier-trapping centers. In Mn doped III-V compound semiconductors, which are proposed for spintronic applications, free carriers play deterministic roles for the magnetic properties and material functionalities. However, by substituting the cation, Mn in III-V acts as an acceptor, resulting in the difficulty to independently change the local-moment and hole concentration. In this contribution, we show how the carrier concentration in (III,Mn)V and the consequent magnetic properties can be precisely tuned by ion irradiation [1, 2].
On one hand, we investigate fundamentally how magnetic properties change upon shifting the Fermi level by hole compensation via ion irradiation. We monitor the change of Curie temperature (TC) and conductivity. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC with carrier compensation over a wide temperature range while the conduction is changed from metallic to insulating. The existence of TC below 10 K is also confirmed in heavily compensated samples. Our experimental results are naturally explained by assuming that the Fermi level resides in the valence band being merged with the Mn-derived impurity band [2].
On the other hand, we explore the application potential of ion irradiation in semiconductor spintronics. We show that the magnetic easy axis of (Ga,Mn)(As,P) can be gradually changed between in-plane and out-of-plane directions [3]. Combined with the possibility of lateral patterning [4], such an approach allows for developing new concepts for spintronic devices.
[1] L. Li, S. Yao, S. Zhou, et al., J. Phys. D: Appl. Phys. 44, 099501 (2011).
[2] S. Zhou, et al., Phys. Rev. B 94, 075205 (2016).
[3] Y. Yuan, ..., S. Zhou, Phys. Rev. Mater. 1, 054401 (2017).
[4] L. Li, ..., S. Zhou, Nucl. Instr. Meth. B 269, 2469-2473 (2011).