Chin. Phys. B Vol. 20, No. 8 (2011) 087503 Determining the sign of g factor via time-resolved Kerr rotation spectroscopy with a rotatable magnetic field ∗ Gu Xiao-Fang(¡), Qian Xuan(a Z), Ji Yang(0 ) † , Chen Lin( ), and Zhao Jian-Hua(ºu) State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China (Received 22 December 2010; revised manuscript received 17 April 2011) Time-resolved Kerr rotation spectroscopy is used to determine the sign of the g factor of carriers in a semiconductor material, with the help of a rotatable magnetic field in the plane of the sample. The spin precession signal of carriers at a fixed time delay is measured as a function of the orientation of the magnetic field with a fixed strength B. The signal has a sine-like form and its phase determines the sign of the g factor of carriers. As a natural extension of previous methods to measure the (time-resolved) photoluminescence or time-resolved Kerr rotation signal as a function of the magnetic field strength with a fixed orientation, such a method gives the correct sign of the g factor of electrons in GaAs. Furthermore, the sign of carriers in a (Ga, Mn)As magnetic semiconductor is also found to be negative. Keywords: g factor, time-resolved Kerr rotation, gallium arsenide, rotatable magnetic field PACS: 75.40.Gb, 76.50.+g, 75.90.+w, 78.67.–n DOI: 10.1088/1674-1056/20/8/087503 1. Introduction In recent years, semiconductor spintronics has at- tracted lots of attention and has been extensively in- vestigated, with the aim to manipulate both the spin and the charge degree of electrons in semiconductors in order to make spin-based post-Moore devices for even more powerful information processing. [1−5] The method of g factor engineering is a candidate for ef- ficient spin-manipulation [6,7] and it requires a knowl- edge of the magnitude and the sign of the g factor of the carriers. Though the magnitude of the g factor can be routinely measured with time-resolved photo- luminescence (TRPL) or time-resolved Kerr rotation (TRKR) techniques, [1,8,9] it is not trivial to determine its sign. Traditionally, the sign of the g factor can be obtained by measuring the circular polarization of photoluminescence (PL) with circularly polarized ex- citation light in a magnetic field (Hanle effect), which is used at an oblique angle to the growth axis. [10−13] Besides this, Kalavich et al. [14] determined the g factor by comparing the circular polarization of the TRPL in an opposite magnetic field. [14] For these methods, the PL singals of semiconductors may have compli- cated origins. TRKR and time-resolved Faraday rota- tion (TRFR) measurement have proved to be power- ful techniques in semiconductor spintronics and they are widely used to study the coherent dynamics of spin. [1,8,9] They can accurately measure the electron spin Larmor precession and, hence, the magnitude of the g factor. However, there are few reports about de- termining the sign of the g factor with TRKR, among which is the work by Yang et al. [15] In their experi- mental configuration, the pump beam and the probe beam had an angle and so the Kerr rotation curve of B> 0 had a time lag relative to that of B< 0, thus giving out the sign of the g factor. 2. Experimental details Here we report on an alternative method to de- termine the sign of the g factor via TRKR measure- ment with a rotatable in-plane magnetic field. This is a natural extension of the previous methods men- tioned above by Snelling et al., [11] Kalavich et al., [14] and Yang et al. [15] The experimental setup is sketched in Fig. 1. The ∗ Project supported by the National Basic Research Program of China (Grant No. 2009CB929301) and the National Natural Science Foundation of China (Grant No. 10911130232). † Corresponding author. E-mail: jiyang@semi.ac.cn © 2011 Chinese Physical Society and IOP Publishing Ltd http://www.iop.org/journals/cpb http://cpb.iphy.ac.cn 087503-1