||This thesis focuses on the two important parts in the spintronic devices based on the spin field effect transistor: (1) the ferromagnetic GaMnAs thin films which is the source-drain material and (2) the Rashba spin-orbit coupling in a two-dimensional electron gas in which the spin can be transported and its polarization can be tuned by external gates. We have grown GaMnAs samples using molecular beam epitaxy (MBE) with Mn composition up to 8%. The intrinsic and extrinsic contribution to the lattice parameter of the low temperature grown GaMnAs is discussed. The influence of the defects on the electrical and magnetic properties of GaMnAs thin films is presented. We have also studied optical properties of GaMnAs thin films and quantum wells using absorption spectrum. The magnetic circular dichroism is employed to study the p-d exchange interaction induced spin splitting. The Rashba spin-orbit coupling in a InGaAs/InA1As two dimensional electron gas (2DEG) is demonstrated by the beating patterns in the Shubnikov de Hass oscillation. Based on the coupling between the spin and orbit momentum, we demonstrates the ways to use spin to drive current by the circular photo galvanic effect (CPGE) and the spin galvanic effect (SGE) with interband excitation. And conversely we show, for the first time, that an electric current can induce spin polarization in a 2DEG, which provides us the opportunity to manipulate spin using electric field instead of magnetic field for the future spintronic devices.