Microstructure and magnetic properties of the ferromagnetic semiconductor Ge1-xMnx following rapid thermal annealing

The group-IV Ge1-xMnx ferromagnetic semiconductor (FMS) has attracted much interest in spintronics due to its compatibility with semiconductor technology. However, Ge1-xMnx FMS prepared at high growth temperature (TS) meets dilemmas in balancing solubility and intermetallic precipitates, limiting its Curie temperature (TC) and electrical tunability. In this study, Ge1-xMnx films were prepared by magnetron sputtering at low TS combined with rapid thermal annealing (RTA). We conducted a systematic study of the microstructure, valence state, and magnetic properties of Ge1-xMnx films. The phase diagram of Ge1-xMnx films versus Mn composition x and RTA temperature TR was plotted, and face-centered cubic structure Ge1-xMnx FMS was achieved with x up to 0.1. As x increased, the hole-mediated ferromagnetism of Ge1-xMnx FMS was enhanced, with the TC reaching 282 K at x = 0.07. We found that the magnetoresistance ratio of Ge1-xMnx FMS was significantly smaller than that of Ge1-xMnx with intermetallic precipitates by two orders, providing an easy method to confirm Ge1-xMnx FMS without intermetallic precipitates. Finally, the mechanism of suppressing the formation of intermetallic compounds by RTA is discussed. Our work extends the preparation window for high-quality Ge1-xMnx FMS, and also provides a promising choice for further investigation of ferromagnetic semiconductors.