Magnetotransport and magneto-optical properties of GaMnAs thin films with high Mn concentrations

III-V-based ferromagnetic-semiconductor (FMS) GaMnAs is a good model system for future semiconductor-spintronics devices. For practical applications, it is important to increase the Curie temperature ($T_{C})$ of GaMnAs (the current record is 173 K) to room temperature. The mean field theory predicts that $T_{C}$ of GaMnAs increases in proportion to its Mn concentration $x$. However, it is difficult to grow GaMnAs with $x \quad >$ 10{\%}, because MnAs clusters and Mn interstitial defects are easily formed in such a high $x$ region. Here, we have successfully grown GaMnAs films with $x$ of 12 - 21{\%} by decreasing the growth temperature to 150-200$^{o}$C and by reducing the film thickness to 10 nm. The magnetic circular dichroism and the anomalous Hall effect measurements indicated that these GaMnAs films have the intrinsic FMS features. A high $T_{C}$ value of 170 K was obtained when $x$ = 12{\%}. This work was partly supported by PRESTO/SORST of JST, Grant-in-aid for Scientific Research, IT Program of RR2002 of MEXT.