Fig. 1. Schematic diagram of the confocal microscope measurement system with a vector magnetic field at low temperature(4 K). The excitation laser with the wavelength of 442 nm is coupled to the measurement system through an optical fiber, the PL of the sample is coupled out to the system through another optical fiber when the sample is excited by the laser, the PL signals are collected by a spectrometer and CCD detector. A SEM image of nanowire is shown in the left bottom of Fig. 1, the scale bar is 1 μm.

Fig. 2. Power dependent PL spectra of different nanowires at 4.2 K: (a) PL spectra from free excitons and defect states with broader linewidth; (b) PL spectra from free excitons and defect states with narrow linewidth; (c) PL spectra from trapped exciton and its phonon replica at lower energy side with a phonon energy of 9.5 meV; (d) PL spectra from trapped excitons and hot polarons at higher energy side with a phonon energy of 5.4 meV.

Fig. 3. PL spectra as a function of magnetic field at low temperature: (a) The peak of free excitons is not effected by the magnetic field while Zeeman splitting is observed for trapped excitons; (b) no splitting observed for both free excitons and trapped excitons; (c) the trapped excitons with a Zeeman effect but not diamagnetic effect; (d) the trapped excitons with both Zeeman effect and diamagnetic effect.

Fig. 4. (a) PL spectra of trapped excitons as a function of magnetic field; (b) (c) g factors of different trapped excitons; (d) (e) the diamagnetic shifts of different trapped excitons.

Fig. 5. The angle dependent PL spectra of trapped exciton (a) and the angle dependent g factors (b) between the magnetic field and the growth direction.